Merge pull request #4014 from hanno-arm/mps_reader

Add MPS reader component
diff --git a/docs/architecture/tls13-experimental.md b/docs/architecture/tls13-experimental.md
index 3db16e0..10cbfa1 100644
--- a/docs/architecture/tls13-experimental.md
+++ b/docs/architecture/tls13-experimental.md
@@ -47,3 +47,22 @@
   Those functions are implemented in `library/ssl_tls13_keys.c` and
   tested in `test_suite_ssl` using test vectors from RFC 8448 and
   https://tls13.ulfheim.net/.
+
+- New TLS Message Processing Stack (MPS)
+
+  The TLS 1.3 prototype is developed alongside a rewrite of the TLS messaging layer,
+  encompassing low-level details such as record parsing, handshake reassembly, and
+  DTLS retransmission state machine.
+
+  MPS has the following components:
+  - Layer 1 (Datagram handling)
+  - Layer 2 (Record handling)
+  - Layer 3 (Message handling)
+  - Layer 4 (Retransmission State Machine)
+  - Reader  (Abstracted pointer arithmetic and reassembly logic for incoming data)
+  - Writer  (Abstracted pointer arithmetic and fragmentation logic for outgoing data)
+
+  Of those components, the following have been upstreamed
+  as part of `MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL`:
+
+  - Reader ([`library/mps_reader.h`](../../library/mps_reader.h))
diff --git a/library/CMakeLists.txt b/library/CMakeLists.txt
index cff4cf9..220fbf9 100644
--- a/library/CMakeLists.txt
+++ b/library/CMakeLists.txt
@@ -47,6 +47,8 @@
     md4.c
     md5.c
     memory_buffer_alloc.c
+    mps_reader.c
+    mps_trace.c
     nist_kw.c
     oid.c
     padlock.c
diff --git a/library/Makefile b/library/Makefile
index 55af96e..13b0b29 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -104,6 +104,8 @@
 	     md4.o \
 	     md5.o \
 	     memory_buffer_alloc.o \
+	     mps_reader.o \
+	     mps_trace.o \
 	     nist_kw.o \
 	     oid.o \
 	     padlock.o \
diff --git a/library/mps_common.h b/library/mps_common.h
new file mode 100644
index 0000000..dd6e31b
--- /dev/null
+++ b/library/mps_common.h
@@ -0,0 +1,195 @@
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+
+/**
+ * \file mps_common.h
+ *
+ * \brief Common functions and macros used by MPS
+ */
+
+#ifndef MBEDTLS_MPS_COMMON_H
+#define MBEDTLS_MPS_COMMON_H
+
+#include "mps_error.h"
+
+#include <stdio.h>
+
+/**
+ * \name SECTION:       MPS Configuration
+ *
+ * \{
+ */
+
+/*! This flag controls whether the MPS-internal components
+ *  (reader, writer, Layer 1-3) perform validation of the
+ *  expected abstract state at the entry of API calls.
+ *
+ *  Context: All MPS API functions impose assumptions/preconditions on the
+ *  context on which they operate. For example, every structure has a notion of
+ *  state integrity which is established by `xxx_init()` and preserved by any
+ *  calls to the MPS API which satisfy their preconditions and either succeed,
+ *  or fail with an error code which is explicitly documented to not corrupt
+ *  structure integrity (such as WANT_READ and WANT_WRITE);
+ *  apart from `xxx_init()` any function assumes state integrity as a
+ *  precondition (but usually more). If any of the preconditions is violated,
+ *  the function's behavior is entirely undefined.
+ *  In addition to state integrity, all MPS structures have a more refined
+ *  notion of abstract state that the API operates on. For example, all layers
+ *  have a notion of 'abtract read state' which indicates if incoming data has
+ *  been passed to the user, e.g. through mps_l2_read_start() for Layer 2
+ *  or mps_l3_read() in Layer 3. After such a call, it doesn't make sense to
+ *  call these reading functions again until the incoming data has been
+ *  explicitly 'consumed', e.g. through mps_l2_read_consume() for Layer 2 or
+ *  mps_l3_read_consume() on Layer 3. However, even if it doesn't make sense,
+ *  it's a design choice whether the API should fail gracefully on such
+ *  non-sensical calls or not, and that's what this option is about:
+ *
+ *  This option determines whether the expected abstract state
+ *  is part of the API preconditions or not: If the option is set,
+ *  then the abstract state is not part of the precondition and is
+ *  thus required to be validated by the implementation. If an unexpected
+ *  abstract state is encountered, the implementation must fail gracefully
+ *  with error #MBEDTLS_ERR_MPS_OPERATION_UNEXPECTED.
+ *  Conversely, if this option is not set, then the expected abstract state
+ *  is included in the preconditions of the respective API calls, and
+ *  an implementation's behaviour is undefined if the abstract state is
+ *  not as expected.
+ *
+ *  For example: Enabling this makes mps_l2_read_done() fail if
+ *  no incoming record is currently open; disabling this would
+ *  lead to undefined behavior in this case.
+ *
+ *  Comment this to remove state validation.
+ */
+#define MBEDTLS_MPS_STATE_VALIDATION
+
+/*! This flag enables/disables assertions on the internal state of MPS.
+ *
+ *  Assertions are sanity checks that should never trigger when MPS
+ *  is used within the bounds of its API and preconditions.
+ *
+ *  Enabling this increases security by limiting the scope of
+ *  potential bugs, but comes at the cost of increased code size.
+ *
+ *  Note: So far, there is no guiding principle as to what
+ *  expected conditions merit an assertion, and which don't.
+ *
+ *  Comment this to disable assertions.
+ */
+#define MBEDTLS_MPS_ENABLE_ASSERTIONS
+
+/*! This flag controls whether tracing for MPS should be enabled. */
+//#define MBEDTLS_MPS_ENABLE_TRACE
+
+#if defined(MBEDTLS_MPS_STATE_VALIDATION)
+
+#define MBEDTLS_MPS_STATE_VALIDATE_RAW( cond, string )                         \
+    do                                                                         \
+    {                                                                          \
+        if( !(cond) )                                                          \
+        {                                                                      \
+            MBEDTLS_MPS_TRACE( mbedtls_mps_trace_error, string );              \
+            MBEDTLS_MPS_TRACE_RETURN( MBEDTLS_ERR_MPS_OPERATION_UNEXPECTED );  \
+        }                                                                      \
+    } while( 0 )
+
+#else /* MBEDTLS_MPS_STATE_VALIDATION */
+
+#define MBEDTLS_MPS_STATE_VALIDATE_RAW( cond, string )           \
+    do                                                           \
+    {                                                            \
+        ( cond );                                                \
+    } while( 0 )
+
+#endif /* MBEDTLS_MPS_STATE_VALIDATION */
+
+#if defined(MBEDTLS_MPS_ENABLE_ASSERTIONS)
+
+#define MBEDTLS_MPS_ASSERT_RAW( cond, string )                          \
+    do                                                                  \
+    {                                                                   \
+        if( !(cond) )                                                   \
+        {                                                               \
+            MBEDTLS_MPS_TRACE( mbedtls_mps_trace_error, string );       \
+            MBEDTLS_MPS_TRACE_RETURN( MBEDTLS_ERR_MPS_INTERNAL_ERROR ); \
+        }                                                               \
+    } while( 0 )
+
+#else /* MBEDTLS_MPS_ENABLE_ASSERTIONS */
+
+#define MBEDTLS_MPS_ASSERT_RAW( cond, string ) do {} while( 0 )
+
+#endif /* MBEDTLS_MPS_ENABLE_ASSERTIONS */
+
+
+/* \} name SECTION: MPS Configuration */
+
+/**
+ * \name SECTION:       Common types
+ *
+ * Various common types used throughout MPS.
+ * \{
+ */
+
+/** \brief   The type of buffer sizes and offsets used in MPS structures.
+ *
+ *           This is an unsigned integer type that should be large enough to
+ *           hold the length of any buffer or message processed by MPS.
+ *
+ *           The reason to pick a value as small as possible here is
+ *           to reduce the size of MPS structures.
+ *
+ * \warning  Care has to be taken when using a narrower type
+ *           than ::mbedtls_mps_size_t here because of
+ *           potential truncation during conversion.
+ *
+ * \warning  Handshake messages in TLS may be up to 2^24 ~ 16Mb in size.
+ *           If mbedtls_mps_[opt_]stored_size_t is smaller than that, the
+ *           maximum handshake message is restricted accordingly.
+ *
+ * For now, we use the default type of size_t throughout, and the use of
+ * smaller types or different types for ::mbedtls_mps_size_t and
+ * ::mbedtls_mps_stored_size_t is not yet supported.
+ *
+ */
+typedef size_t mbedtls_mps_stored_size_t;
+#define MBEDTLS_MPS_STORED_SIZE_MAX  ( (mbedtls_mps_stored_size_t) -1 )
+
+/** \brief The type of buffer sizes and offsets used in the MPS API
+ *         and implementation.
+ *
+ *         This must be at least as wide as ::mbedtls_stored_size_t but
+ *         may be chosen to be strictly larger if more suitable for the
+ *         target architecture.
+ *
+ *         For example, in a test build for ARM Thumb, using uint_fast16_t
+ *         instead of uint16_t reduced the code size from 1060 Byte to 962 Byte,
+ *         so almost 10%.
+ */
+typedef size_t mbedtls_mps_size_t;
+#define MBEDTLS_MPS_SIZE_MAX  ( (mbedtls_mps_size_t) -1 )
+
+#if MBEDTLS_MPS_STORED_SIZE_MAX > MBEDTLS_MPS_SIZE_MAX
+#error "Misconfiguration of mbedtls_mps_size_t and mbedtls_mps_stored_size_t."
+#endif
+
+/* \} SECTION: Common types */
+
+
+#endif /* MBEDTLS_MPS_COMMON_H */
diff --git a/library/mps_error.h b/library/mps_error.h
new file mode 100644
index 0000000..f78d9a0
--- /dev/null
+++ b/library/mps_error.h
@@ -0,0 +1,103 @@
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+
+/**
+ * \file mps_error.h
+ *
+ * \brief Error codes used by MPS
+ */
+
+#ifndef MBEDTLS_MPS_ERROR_H
+#define MBEDTLS_MPS_ERROR_H
+
+
+/* TODO: The error code allocation needs to be revisited:
+ *
+ * - Should we make (some of) the MPS Reader error codes public?
+ *   If so, we need to adjust MBEDTLS_MPS_READER_MAKE_ERROR() to hit
+ *   a gap in the Mbed TLS public error space.
+ *   If not, we have to make sure we don't forward those errors
+ *   at the level of the public API -- no risk at the moment as
+ *   long as MPS is an experimental component not accessible from
+ *   public API.
+ */
+
+/**
+ * \name SECTION:       MPS general error codes
+ *
+ * \{
+ */
+
+#ifndef MBEDTLS_MPS_ERR_BASE
+#define MBEDTLS_MPS_ERR_BASE ( 0 )
+#endif
+
+#define MBEDTLS_MPS_MAKE_ERROR(code) \
+    ( -( MBEDTLS_MPS_ERR_BASE | (code) ) )
+
+#define MBEDTLS_ERR_MPS_OPERATION_UNEXPECTED  MBEDTLS_MPS_MAKE_ERROR( 0x1 )
+#define MBEDTLS_ERR_MPS_INTERNAL_ERROR        MBEDTLS_MPS_MAKE_ERROR( 0x2 )
+
+/* \} name SECTION: MPS general error codes */
+
+/**
+ * \name SECTION:       MPS Reader error codes
+ *
+ * \{
+ */
+
+#ifndef MBEDTLS_MPS_READER_ERR_BASE
+#define MBEDTLS_MPS_READER_ERR_BASE ( 1 << 8 )
+#endif
+
+#define MBEDTLS_MPS_READER_MAKE_ERROR(code) \
+    ( -( MBEDTLS_MPS_READER_ERR_BASE | (code) ) )
+
+/*! An attempt to reclaim the data buffer from a reader failed because
+ *  the user hasn't yet read and committed all of it. */
+#define MBEDTLS_ERR_MPS_READER_DATA_LEFT             MBEDTLS_MPS_READER_MAKE_ERROR( 0x1 )
+
+/*! An invalid argument was passed to the reader. */
+#define MBEDTLS_ERR_MPS_READER_INVALID_ARG           MBEDTLS_MPS_READER_MAKE_ERROR( 0x2 )
+
+/*! An attempt to move a reader to consuming mode through mbedtls_mps_reader_feed()
+ *  after pausing failed because the provided data is not sufficient to serve the
+ *  read requests that led to the pausing. */
+#define MBEDTLS_ERR_MPS_READER_NEED_MORE             MBEDTLS_MPS_READER_MAKE_ERROR( 0x3 )
+
+/*! A get request failed because not enough data is available in the reader. */
+#define MBEDTLS_ERR_MPS_READER_OUT_OF_DATA           MBEDTLS_MPS_READER_MAKE_ERROR( 0x4 )
+
+/*!< A get request after pausing and reactivating the reader failed because
+ *   the request is not in line with the request made prior to pausing. The user
+ *   must not change it's 'strategy' after pausing and reactivating a reader. */
+#define MBEDTLS_ERR_MPS_READER_INCONSISTENT_REQUESTS MBEDTLS_MPS_READER_MAKE_ERROR( 0x5 )
+
+/*! An attempt to reclaim the data buffer from a reader failed because the reader
+ *  has no accumulator it can use to backup the data that hasn't been processed. */
+#define MBEDTLS_ERR_MPS_READER_NEED_ACCUMULATOR      MBEDTLS_MPS_READER_MAKE_ERROR( 0x6 )
+
+/*! An attempt to reclaim the data buffer from a reader failed because the
+ *  accumulator passed to the reader is not large enough to hold both the
+ *  data that hasn't been processed and the excess of the last read-request. */
+#define MBEDTLS_ERR_MPS_READER_ACCUMULATOR_TOO_SMALL MBEDTLS_MPS_READER_MAKE_ERROR( 0x7 )
+
+/* \} name SECTION: MPS Reader error codes */
+
+#endif /* MBEDTLS_MPS_ERROR_H */
diff --git a/library/mps_reader.c b/library/mps_reader.c
new file mode 100644
index 0000000..848634d
--- /dev/null
+++ b/library/mps_reader.c
@@ -0,0 +1,564 @@
+/*
+ *  Message Processing Stack, Reader implementation
+ *
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of Mbed TLS (https://tls.mbed.org)
+ */
+
+#include "common.h"
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
+
+#include "mps_reader.h"
+#include "mps_common.h"
+#include "mps_trace.h"
+
+#include <string.h>
+
+#if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \
+    !defined(inline) && !defined(__cplusplus)
+#define inline __inline
+#endif
+
+#if defined(MBEDTLS_MPS_ENABLE_TRACE)
+static int mbedtls_mps_trace_id = MBEDTLS_MPS_TRACE_BIT_READER;
+#endif /* MBEDTLS_MPS_ENABLE_TRACE */
+
+/*
+ * GENERAL NOTE ON CODING STYLE
+ *
+ * The following code intentionally separates memory loads
+ * and stores from other operations (arithmetic or branches).
+ * This leads to the introduction of many local variables
+ * and significantly increases the C-code line count, but
+ * should not increase the size of generated assembly.
+ *
+ * The reason for this is twofold:
+ * (1) It will ease verification efforts using the VST
+ *     (Verified Software Toolchain)
+ *     whose program logic cannot directly reason
+ *     about instructions containing a load or store in
+ *     addition to other operations (e.g. *p = *q or
+ *     tmp = *p + 42).
+ * (2) Operating on local variables and writing the results
+ *     back to the target contexts on success only
+ *     allows to maintain structure invariants even
+ *     on failure - this in turn has two benefits:
+ *     (2.a) If for some reason an error code is not caught
+ *           and operation continues, functions are nonetheless
+ *           called with sane contexts, reducing the risk
+ *           of dangerous behavior.
+ *     (2.b) Randomized testing is easier if structures
+ *           remain intact even in the face of failing
+ *           and/or non-sensical calls.
+ *     Moreover, it might even reduce code-size because
+ *     the compiler need not write back temporary results
+ *     to memory in case of failure.
+ *
+ */
+
+static inline int mps_reader_is_accumulating(
+    mbedtls_mps_reader const *rd )
+{
+    mbedtls_mps_size_t acc_remaining;
+    if( rd->acc == NULL )
+        return( 0 );
+
+    acc_remaining = rd->acc_share.acc_remaining;
+    return( acc_remaining > 0 );
+}
+
+static inline int mps_reader_is_producing(
+    mbedtls_mps_reader const *rd )
+{
+    unsigned char *frag = rd->frag;
+    return( frag == NULL );
+}
+
+static inline int mps_reader_is_consuming(
+    mbedtls_mps_reader const *rd )
+{
+    return( !mps_reader_is_producing( rd ) );
+}
+
+static inline mbedtls_mps_size_t mps_reader_get_fragment_offset(
+    mbedtls_mps_reader const *rd )
+{
+    unsigned char *acc = rd->acc;
+    mbedtls_mps_size_t frag_offset;
+
+    if( acc == NULL )
+        return( 0 );
+
+    frag_offset = rd->acc_share.frag_offset;
+    return( frag_offset );
+}
+
+static inline mbedtls_mps_size_t mps_reader_serving_from_accumulator(
+    mbedtls_mps_reader const *rd )
+{
+    mbedtls_mps_size_t frag_offset, end;
+
+    frag_offset = mps_reader_get_fragment_offset( rd );
+    end = rd->end;
+
+    return( end < frag_offset );
+}
+
+static inline void mps_reader_zero( mbedtls_mps_reader *rd )
+{
+    /* A plain memset() would likely be more efficient,
+     * but the current way of zeroing makes it harder
+     * to overlook fields which should not be zero-initialized.
+     * It's also more suitable for FV efforts since it
+     * doesn't require reasoning about structs being
+     * interpreted as unstructured binary blobs. */
+    static mbedtls_mps_reader const zero =
+        { .frag          = NULL,
+          .frag_len      = 0,
+          .commit        = 0,
+          .end           = 0,
+          .pending       = 0,
+          .acc           = NULL,
+          .acc_len       = 0,
+          .acc_available = 0,
+          .acc_share     = { .acc_remaining = 0 }
+        };
+    *rd = zero;
+}
+
+int mbedtls_mps_reader_init( mbedtls_mps_reader *rd,
+                             unsigned char *acc,
+                             mbedtls_mps_size_t acc_len )
+{
+    MBEDTLS_MPS_TRACE_INIT( "mbedtls_mps_reader_init" );
+    MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                       "* Accumulator size: %u bytes", (unsigned) acc_len );
+    mps_reader_zero( rd );
+    rd->acc = acc;
+    rd->acc_len = acc_len;
+    MBEDTLS_MPS_TRACE_RETURN( 0 );
+}
+
+int mbedtls_mps_reader_free( mbedtls_mps_reader *rd )
+{
+    MBEDTLS_MPS_TRACE_INIT( "mbedtls_mps_reader_free" );
+    mps_reader_zero( rd );
+    MBEDTLS_MPS_TRACE_RETURN( 0 );
+}
+
+int mbedtls_mps_reader_feed( mbedtls_mps_reader *rd,
+                             unsigned char *new_frag,
+                             mbedtls_mps_size_t new_frag_len )
+{
+    mbedtls_mps_size_t copy_to_acc;
+    MBEDTLS_MPS_TRACE_INIT( "mbedtls_mps_reader_feed" );
+    MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                       "* Fragment length: %u bytes", (unsigned) new_frag_len );
+
+    if( new_frag == NULL )
+        MBEDTLS_MPS_TRACE_RETURN( MBEDTLS_ERR_MPS_READER_INVALID_ARG );
+
+    MBEDTLS_MPS_STATE_VALIDATE_RAW( mps_reader_is_producing( rd ),
+        "mbedtls_mps_reader_feed() requires reader to be in producing mode" );
+
+    if( mps_reader_is_accumulating( rd ) )
+    {
+        unsigned char *acc    = rd->acc;
+        mbedtls_mps_size_t acc_remaining = rd->acc_share.acc_remaining;
+        mbedtls_mps_size_t acc_available = rd->acc_available;
+
+        /* Skip over parts of the accumulator that have already been filled. */
+        acc += acc_available;
+
+        copy_to_acc = acc_remaining;
+        if( copy_to_acc > new_frag_len )
+            copy_to_acc = new_frag_len;
+
+        /* Copy new contents to accumulator. */
+        memcpy( acc, new_frag, copy_to_acc );
+
+        MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                "Copy new data of size %u of %u into accumulator at offset %u",
+                (unsigned) copy_to_acc, (unsigned) new_frag_len, (unsigned) acc_available );
+
+        /* Check if, with the new fragment, we have enough data. */
+        acc_remaining -= copy_to_acc;
+        if( acc_remaining > 0 )
+        {
+            /* We need to accumulate more data. Stay in producing mode. */
+            acc_available += copy_to_acc;
+            rd->acc_share.acc_remaining = acc_remaining;
+            rd->acc_available = acc_available;
+            MBEDTLS_MPS_TRACE_RETURN( MBEDTLS_ERR_MPS_READER_NEED_MORE );
+        }
+
+        /* We have filled the accumulator: Move to consuming mode. */
+
+        MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                           "Enough data available to serve user request" );
+
+        /* Remember overlap of accumulator and fragment. */
+        rd->acc_share.frag_offset = acc_available;
+        acc_available += copy_to_acc;
+        rd->acc_available = acc_available;
+    }
+    else /* Not accumulating */
+    {
+        rd->acc_share.frag_offset = 0;
+    }
+
+    rd->frag = new_frag;
+    rd->frag_len = new_frag_len;
+    rd->commit = 0;
+    rd->end = 0;
+    MBEDTLS_MPS_TRACE_RETURN( 0 );
+}
+
+
+int mbedtls_mps_reader_get( mbedtls_mps_reader *rd,
+                            mbedtls_mps_size_t desired,
+                            unsigned char **buffer,
+                            mbedtls_mps_size_t *buflen )
+{
+    unsigned char *frag;
+    mbedtls_mps_size_t frag_len, frag_offset, end, frag_fetched, frag_remaining;
+    MBEDTLS_MPS_TRACE_INIT( "mbedtls_mps_reader_get" );
+    MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                       "* Bytes requested: %u", (unsigned) desired );
+
+    MBEDTLS_MPS_STATE_VALIDATE_RAW( mps_reader_is_consuming( rd ),
+          "mbedtls_mps_reader_get() requires reader to be in consuming mode" );
+
+    end = rd->end;
+    frag_offset = mps_reader_get_fragment_offset( rd );
+
+    /* Check if we're still serving from the accumulator. */
+    if( mps_reader_serving_from_accumulator( rd ) )
+    {
+        /* Illustration of supported and unsupported cases:
+         *
+         * - Allowed #1
+         *
+         *                          +-----------------------------------+
+         *                          |               frag                |
+         *                          +-----------------------------------+
+         *
+         *             end end+desired
+         *              |       |
+         *        +-----v-------v-------------+
+         *        |          acc              |
+         *        +---------------------------+
+         *                          |         |
+         *                     frag_offset  acc_available
+         *
+         * - Allowed #2
+         *
+         *                          +-----------------------------------+
+         *                          |               frag                |
+         *                          +-----------------------------------+
+         *
+         *                  end          end+desired
+         *                   |                |
+         *        +----------v----------------v
+         *        |          acc              |
+         *        +---------------------------+
+         *                          |         |
+         *                   frag_offset acc_available
+         *
+         * - Not allowed #1 (could be served, but we don't actually use it):
+         *
+         *                      +-----------------------------------+
+         *                      |               frag                |
+         *                      +-----------------------------------+
+         *
+         *              end        end+desired
+         *               |             |
+         *        +------v-------------v------+
+         *        |          acc              |
+         *        +---------------------------+
+         *                      |             |
+         *                frag_offset   acc_available
+         *
+         *
+         * - Not allowed #2 (can't be served with a contiguous buffer):
+         *
+         *                      +-----------------------------------+
+         *                      |               frag                |
+         *                      +-----------------------------------+
+         *
+         *              end                 end + desired
+         *               |                        |
+         *        +------v--------------------+   v
+         *        |            acc            |
+         *        +---------------------------+
+         *                      |             |
+         *                frag_offset   acc_available
+         *
+         * In case of Allowed #2 we're switching to serve from
+         * `frag` starting from the next call to mbedtls_mps_reader_get().
+         */
+
+        unsigned char *acc;
+
+        MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                           "Serve the request from the accumulator" );
+        if( frag_offset - end < desired )
+        {
+            mbedtls_mps_size_t acc_available;
+            acc_available = rd->acc_available;
+            if( acc_available - end != desired )
+            {
+                /* It might be possible to serve some of these situations by
+                 * making additional space in the accumulator, removing those
+                 * parts that have already been committed.
+                 * On the other hand, this brings additional complexity and
+                 * enlarges the code size, while there doesn't seem to be a use
+                 * case where we don't attempt exactly the same `get` calls when
+                 * resuming on a reader than what we tried before pausing it.
+                 * If we believe we adhere to this restricted usage throughout
+                 * the library, this check is a good opportunity to
+                 * validate this. */
+                MBEDTLS_MPS_TRACE_RETURN(
+                    MBEDTLS_ERR_MPS_READER_INCONSISTENT_REQUESTS );
+            }
+        }
+
+        acc = rd->acc;
+        acc += end;
+
+        *buffer = acc;
+        if( buflen != NULL )
+            *buflen = desired;
+
+        end += desired;
+        rd->end = end;
+        rd->pending = 0;
+
+        MBEDTLS_MPS_TRACE_RETURN( 0 );
+    }
+
+    /* Attempt to serve the request from the current fragment */
+    MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                       "Serve the request from the current fragment." );
+
+    frag_len = rd->frag_len;
+    frag_fetched = end - frag_offset; /* The amount of data from the current
+                                       * fragment that has already been passed
+                                       * to the user. */
+    frag_remaining = frag_len - frag_fetched; /* Remaining data in fragment */
+
+    /* Check if we can serve the read request from the fragment. */
+    if( frag_remaining < desired )
+    {
+        MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                           "There's not enough data in the current fragment "
+                           "to serve the request." );
+        /* There's not enough data in the current fragment,
+         * so either just RETURN what we have or fail. */
+        if( buflen == NULL )
+        {
+            if( frag_remaining > 0 )
+            {
+                rd->pending = desired - frag_remaining;
+                MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                       "Remember to collect %u bytes before re-opening",
+                       (unsigned) rd->pending );
+            }
+            MBEDTLS_MPS_TRACE_RETURN( MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+        }
+
+        desired = frag_remaining;
+    }
+
+    /* There's enough data in the current fragment to serve the
+     * (potentially modified) read request. */
+
+    frag = rd->frag;
+    frag += frag_fetched;
+
+    *buffer = frag;
+    if( buflen != NULL )
+        *buflen = desired;
+
+    end += desired;
+    rd->end = end;
+    rd->pending = 0;
+    MBEDTLS_MPS_TRACE_RETURN( 0 );
+}
+
+int mbedtls_mps_reader_commit( mbedtls_mps_reader *rd )
+{
+    mbedtls_mps_size_t end;
+    MBEDTLS_MPS_TRACE_INIT( "mbedtls_mps_reader_commit" );
+    MBEDTLS_MPS_STATE_VALIDATE_RAW( mps_reader_is_consuming( rd ),
+       "mbedtls_mps_reader_commit() requires reader to be in consuming mode" );
+
+    end = rd->end;
+    rd->commit = end;
+
+    MBEDTLS_MPS_TRACE_RETURN( 0 );
+}
+
+int mbedtls_mps_reader_reclaim( mbedtls_mps_reader *rd,
+                                int *paused )
+{
+    unsigned char *frag, *acc;
+    mbedtls_mps_size_t pending, commit;
+    mbedtls_mps_size_t acc_len, frag_offset, frag_len;
+    MBEDTLS_MPS_TRACE_INIT( "mbedtls_mps_reader_reclaim" );
+
+    if( paused != NULL )
+        *paused = 0;
+
+    MBEDTLS_MPS_STATE_VALIDATE_RAW( mps_reader_is_consuming( rd ),
+       "mbedtls_mps_reader_reclaim() requires reader to be in consuming mode" );
+
+    frag     = rd->frag;
+    acc      = rd->acc;
+    pending  = rd->pending;
+    commit   = rd->commit;
+    frag_len = rd->frag_len;
+
+    frag_offset = mps_reader_get_fragment_offset( rd );
+
+    if( pending == 0 )
+    {
+        MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                           "No unsatisfied read-request has been logged." );
+
+        /* Check if there's data left to be consumed. */
+        if( commit < frag_offset || commit - frag_offset < frag_len )
+        {
+            MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                               "There is data left to be consumed." );
+            rd->end = commit;
+            MBEDTLS_MPS_TRACE_RETURN( MBEDTLS_ERR_MPS_READER_DATA_LEFT );
+        }
+
+        rd->acc_available = 0;
+        rd->acc_share.acc_remaining = 0;
+
+        MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                           "Fragment has been fully processed and committed." );
+    }
+    else
+    {
+        int overflow;
+
+        mbedtls_mps_size_t acc_backup_offset;
+        mbedtls_mps_size_t acc_backup_len;
+        mbedtls_mps_size_t frag_backup_offset;
+        mbedtls_mps_size_t frag_backup_len;
+
+        mbedtls_mps_size_t backup_len;
+        mbedtls_mps_size_t acc_len_needed;
+
+        MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+               "There has been an unsatisfied read with %u bytes overhead.",
+               (unsigned) pending );
+
+        if( acc == NULL )
+        {
+            MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                               "No accumulator present" );
+            MBEDTLS_MPS_TRACE_RETURN(
+                MBEDTLS_ERR_MPS_READER_NEED_ACCUMULATOR );
+        }
+        acc_len = rd->acc_len;
+
+        /* Check if the upper layer has already fetched
+         * and committed the contents of the accumulator. */
+        if( commit < frag_offset )
+        {
+            /* No, accumulator is still being processed. */
+            frag_backup_offset = 0;
+            frag_backup_len = frag_len;
+            acc_backup_offset = commit;
+            acc_backup_len = frag_offset - commit;
+        }
+        else
+        {
+            /* Yes, the accumulator is already processed. */
+            frag_backup_offset = commit - frag_offset;
+            frag_backup_len = frag_len - frag_backup_offset;
+            acc_backup_offset = 0;
+            acc_backup_len = 0;
+        }
+
+        backup_len = acc_backup_len + frag_backup_len;
+        acc_len_needed = backup_len + pending;
+
+        overflow  = 0;
+        overflow |= ( backup_len     < acc_backup_len );
+        overflow |= ( acc_len_needed < backup_len );
+
+        if( overflow || acc_len < acc_len_needed )
+        {
+            /* Except for the different return code, we behave as if
+             * there hadn't been a call to mbedtls_mps_reader_get()
+             * since the last commit. */
+            rd->end = commit;
+            rd->pending = 0;
+            MBEDTLS_MPS_TRACE( mbedtls_mps_trace_error,
+                               "The accumulator is too small to handle the backup." );
+            MBEDTLS_MPS_TRACE( mbedtls_mps_trace_error,
+                               "* Size: %u", (unsigned) acc_len );
+            MBEDTLS_MPS_TRACE( mbedtls_mps_trace_error,
+                               "* Needed: %u (%u + %u)",
+                               (unsigned) acc_len_needed,
+                               (unsigned) backup_len, (unsigned) pending );
+            MBEDTLS_MPS_TRACE_RETURN(
+                MBEDTLS_ERR_MPS_READER_ACCUMULATOR_TOO_SMALL );
+        }
+
+        MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                         "Fragment backup: %u", (unsigned) frag_backup_len );
+        MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                         "Accumulator backup: %u", (unsigned) acc_backup_len );
+
+        /* Move uncommitted parts from the accumulator to the front
+         * of the accumulator. */
+        memmove( acc, acc + acc_backup_offset, acc_backup_len );
+
+        /* Copy uncmmitted parts of the current fragment to the
+         * accumulator. */
+        memcpy( acc + acc_backup_len,
+                frag + frag_backup_offset, frag_backup_len );
+
+        rd->acc_available = backup_len;
+        rd->acc_share.acc_remaining = pending;
+
+        if( paused != NULL )
+            *paused = 1;
+    }
+
+    rd->frag     = NULL;
+    rd->frag_len = 0;
+
+    rd->commit  = 0;
+    rd->end     = 0;
+    rd->pending = 0;
+
+    MBEDTLS_MPS_TRACE( mbedtls_mps_trace_comment,
+                       "Final state: aa %u, al %u, ar %u",
+                       (unsigned) rd->acc_available, (unsigned) rd->acc_len,
+                       (unsigned) rd->acc_share.acc_remaining );
+    MBEDTLS_MPS_TRACE_RETURN( 0 );
+}
+
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
diff --git a/library/mps_reader.h b/library/mps_reader.h
new file mode 100644
index 0000000..427c1bd
--- /dev/null
+++ b/library/mps_reader.h
@@ -0,0 +1,382 @@
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+
+/**
+ * \file mps_reader.h
+ *
+ * \brief This file defines reader objects, which together with their
+ *        sibling writer objects form the basis for the communication
+ *        between the various layers of the Mbed TLS messaging stack,
+ *        as well as the communication between the messaging stack and
+ *        the (D)TLS handshake protocol implementation.
+ *
+ * Readers provide a means of transferring incoming data from
+ * a 'producer' providing it in chunks of arbitrary size, to
+ * a 'consumer' which fetches and processes it in chunks of
+ * again arbitrary, and potentially different, size.
+ *
+ * Readers can thus be seen as datagram-to-stream converters,
+ * and they abstract away the following two tasks from the user:
+ * 1. The pointer arithmetic of stepping through a producer-
+ *    provided chunk in smaller chunks.
+ * 2. The merging of incoming data chunks in case the
+ *    consumer requests data in larger chunks than what the
+ *    producer provides.
+ *
+ * The basic abstract flow of operation is the following:
+ * - Initially, the reader is in 'producing mode'.
+ * - The producer hands an incoming data buffer to the reader,
+ *   moving it from 'producing' to 'consuming' mode.
+ * - The consumer subsequently fetches and processes the buffer
+ *   content. Once that's done -- or partially done and a consumer's
+ *   request can't be fulfilled -- the producer revokes the reader's
+ *   access to the incoming data buffer, putting the reader back to
+ *   producing mode.
+ * - The producer subsequently gathers more incoming data and hands
+ *   it to the reader until it switches back to consuming mode
+ *   if enough data is available for the last consumer request to
+ *   be satisfiable.
+ * - Repeat the above.
+ *
+ * The abstract states of the reader from the producer's and
+ * consumer's perspective are as follows:
+ *
+ * - From the perspective of the consumer, the state of the
+ *   reader consists of the following:
+ *   - A byte stream representing (concatenation of) the data
+ *     received through calls to mbedtls_mps_reader_get(),
+ *   - A marker within that byte stream indicating which data
+ *     can be considered processed, and hence need not be retained,
+ *     when the reader is passed back to the producer via
+ *     mbedtls_mps_reader_reclaim().
+ *     The marker is set via mbedtls_mps_reader_commit()
+ *     which places it at the end of the current byte stream.
+ *   The consumer need not be aware of the distinction between consumer
+ *   and producer mode, because it only interfaces with the reader
+ *   when the latter is in consuming mode.
+ *
+ * - From the perspective of the producer, the reader's state is one of:
+ *   - Attached: The reader is in consuming mode.
+ *   - Unset: No incoming data buffer is currently managed by the reader,
+ *            and all previously handed incoming data buffers have been
+ *            fully processed. More data needs to be fed into the reader
+ *            via mbedtls_mps_reader_feed().
+ *
+ *   - Accumulating: No incoming data buffer is currently managed by the
+ *                   reader, but some data from the previous incoming data
+ *                   buffer hasn't been processed yet and is internally
+ *                   held back.
+ *   The Attached state belongs to consuming mode, while the Unset and
+ *   Accumulating states belong to producing mode.
+ *
+ * Transitioning from the Unset or Accumulating state to Attached is
+ * done via successful calls to mbedtls_mps_reader_feed(), while
+ * transitioning from Attached to either Unset or Accumulating (depending
+ * on what has been processed) is done via mbedtls_mps_reader_reclaim().
+ *
+ * The following diagram depicts the producer-state progression:
+ *
+ *        +------------------+             reclaim
+ *        |      Unset       +<-------------------------------------+       get
+ *        +--------|---------+                                      |   +------+
+ *                 |                                                |   |      |
+ *                 |                                                |   |      |
+ *                 |                feed                  +---------+---+--+   |
+ *                 +-------------------------------------->                <---+
+ *                                                        |    Attached    |
+ *                 +-------------------------------------->                <---+
+ *                 |     feed, enough data available      +---------+---+--+   |
+ *                 |     to serve previous consumer request         |   |      |
+ *                 |                                                |   |      |
+ *        +--------+---------+                                      |   +------+
+ *   +---->   Accumulating   |<-------------------------------------+    commit
+ *   |    +---+--------------+      reclaim, previous read request
+ *   |        |                        couldn't be fulfilled
+ *   |        |
+ *   +--------+
+ *     feed, need more data to serve
+ *     previous consumer request
+ *                                         |
+ *                                         |
+ *               producing mode            |           consuming mode
+ *                                         |
+ *
+ */
+
+#ifndef MBEDTLS_READER_H
+#define MBEDTLS_READER_H
+
+#include <stdio.h>
+
+#include "mps_common.h"
+#include "mps_error.h"
+
+struct mbedtls_mps_reader;
+typedef struct mbedtls_mps_reader mbedtls_mps_reader;
+
+/*
+ * Structure definitions
+ */
+
+struct mbedtls_mps_reader
+{
+    unsigned char *frag;  /*!< The fragment of incoming data managed by
+                           *   the reader; it is provided to the reader
+                           *   through mbedtls_mps_reader_feed(). The reader
+                           *   does not own the fragment and does not
+                           *   perform any allocation operations on it,
+                           *   but does have read and write access to it.
+                           *
+                           *   The reader is in consuming mode if
+                           *   and only if \c frag is not \c NULL.          */
+    mbedtls_mps_stored_size_t frag_len;
+                          /*!< The length of the current fragment.
+                           *   Must be 0 if \c frag == \c NULL.             */
+    mbedtls_mps_stored_size_t commit;
+                          /*!< The offset of the last commit, relative
+                           *   to the first byte in the fragment, if
+                           *   no accumulator is present. If an accumulator
+                           *   is present, it is viewed as a prefix to the
+                           *   current fragment, and this variable contains
+                           *   an offset from the beginning of the accumulator.
+                           *
+                           *   This is only used when the reader is in
+                           *   consuming mode, i.e. \c frag != \c NULL;
+                           *   otherwise, its value is \c 0.                */
+    mbedtls_mps_stored_size_t end;
+                          /*!< The offset of the end of the last chunk
+                           *   passed to the user through a call to
+                           *   mbedtls_mps_reader_get(), relative to the first
+                           *   byte in the fragment, if no accumulator is
+                           *   present. If an accumulator is present, it is
+                           *   viewed as a prefix to the current fragment, and
+                           *   this variable contains an offset from the
+                           *   beginning of the accumulator.
+                           *
+                           *   This is only used when the reader is in
+                           *   consuming mode, i.e. \c frag != \c NULL;
+                           *   otherwise, its value is \c 0.                */
+    mbedtls_mps_stored_size_t pending;
+                          /*!< The amount of incoming data missing on the
+                           *   last call to mbedtls_mps_reader_get().
+                           *   In particular, it is \c 0 if the last call
+                           *   was successful.
+                           *   If a reader is reclaimed after an
+                           *   unsuccessful call to mbedtls_mps_reader_get(),
+                           *   this variable is used to have the reader
+                           *   remember how much data should be accumulated
+                           *   so that the call to mbedtls_mps_reader_get()
+                           *   succeeds next time.
+                           *   This is only used when the reader is in
+                           *   consuming mode, i.e. \c frag != \c NULL;
+                           *   otherwise, its value is \c 0.                */
+
+    /* The accumulator is only needed if we need to be able to pause
+     * the reader. A few bytes could be saved by moving this to a
+     * separate struct and using a pointer here. */
+
+    unsigned char *acc;   /*!< The accumulator is used to gather incoming
+                           *   data if a read-request via mbedtls_mps_reader_get()
+                           *   cannot be served from the current fragment.   */
+    mbedtls_mps_stored_size_t acc_len;
+                           /*!< The total size of the accumulator.           */
+    mbedtls_mps_stored_size_t acc_available;
+                          /*!< The number of bytes currently gathered in
+                           *   the accumulator. This is both used in
+                           *   producing and in consuming mode:
+                           *   While producing, it is increased until
+                           *   it reaches the value of \c acc_remaining below.
+                           *   While consuming, it is used to judge if a
+                           *   get request can be served from the
+                           *   accumulator or not.
+                           *   Must not be larger than \c acc_len.           */
+    union
+    {
+        mbedtls_mps_stored_size_t acc_remaining;
+                              /*!< This indicates the amount of data still
+                               *   to be gathered in the accumulator. It is
+                               *   only used in producing mode.
+                               *   Must be at most acc_len - acc_available.  */
+        mbedtls_mps_stored_size_t frag_offset;
+                              /*!< If an accumulator is present and in use, this
+                               *   field indicates the offset of the current
+                               *   fragment from the beginning of the
+                               *   accumulator. If no accumulator is present
+                               *   or the accumulator is not in use, this is \c 0.
+                               *   It is only used in consuming mode.
+                               *   Must not be larger than \c acc_available. */
+    } acc_share;
+};
+
+/*
+ * API organization:
+ * A reader object is usually prepared and maintained
+ * by some lower layer and passed for usage to an upper
+ * layer, and the API naturally splits according to which
+ * layer is supposed to use the respective functions.
+ */
+
+/*
+ * Maintenance API (Lower layer)
+ */
+
+/**
+ * \brief           Initialize a reader object
+ *
+ * \param reader    The reader to be initialized.
+ * \param acc       The buffer to be used as a temporary accumulator
+ *                  in case get requests through mbedtls_mps_reader_get()
+ *                  exceed the buffer provided by mbedtls_mps_reader_feed().
+ *                  This buffer is owned by the caller and exclusive use
+ *                  for reading and writing is given to the reader for the
+ *                  duration of the reader's lifetime. It is thus the caller's
+ *                  responsibility to maintain (and not touch) the buffer for
+ *                  the lifetime of the reader, and to properly zeroize and
+ *                  free the memory after the reader has been destroyed.
+ * \param acc_len   The size in Bytes of \p acc.
+ *
+ * \return          \c 0 on success.
+ * \return          A negative \c MBEDTLS_ERR_READER_XXX error code on failure.
+ */
+int mbedtls_mps_reader_init( mbedtls_mps_reader *reader,
+                             unsigned char *acc,
+                             mbedtls_mps_size_t acc_len );
+
+/**
+ * \brief           Free a reader object
+ *
+ * \param reader    The reader to be freed.
+ *
+ * \return          \c 0 on success.
+ * \return          A negative \c MBEDTLS_ERR_READER_XXX error code on failure.
+ */
+int mbedtls_mps_reader_free( mbedtls_mps_reader *reader );
+
+/**
+ * \brief           Pass chunk of data for the reader to manage.
+ *
+ * \param reader    The reader context to use. The reader must be
+ *                  in producing mode.
+ * \param buf       The buffer to be managed by the reader.
+ * \param buflen    The size in Bytes of \p buffer.
+ *
+ * \return          \c 0 on success. In this case, the reader will be
+ *                  moved to consuming mode and obtains read access
+ *                  of \p buf until mbedtls_mps_reader_reclaim()
+ *                  is called. It is the responsibility of the caller
+ *                  to ensure that the \p buf persists and is not changed
+ *                  between successful calls to mbedtls_mps_reader_feed()
+ *                  and mbedtls_mps_reader_reclaim().
+ * \return          \c MBEDTLS_ERR_MPS_READER_NEED_MORE if more input data is
+ *                  required to fulfill a previous request to mbedtls_mps_reader_get().
+ *                  In this case, the reader remains in producing mode and
+ *                  takes no ownership of the provided buffer (an internal copy
+ *                  is made instead).
+ * \return          Another negative \c MBEDTLS_ERR_READER_XXX error code on
+ *                  different kinds of failures.
+ */
+int mbedtls_mps_reader_feed( mbedtls_mps_reader *reader,
+                             unsigned char *buf,
+                             mbedtls_mps_size_t buflen );
+
+/**
+ * \brief           Reclaim reader's access to the current input buffer.
+ *
+ * \param reader    The reader context to use. The reader must be
+ *                  in consuming mode.
+ * \param paused    If not \c NULL, the integer at address \p paused will be
+ *                  modified to indicate whether the reader has been paused
+ *                  (value \c 1) or not (value \c 0). Pausing happens if there
+ *                  is uncommitted data and a previous request to
+ *                  mbedtls_mps_reader_get() has exceeded the bounds of the
+ *                  input buffer.
+ *
+ * \return          \c 0 on success.
+ * \return          A negative \c MBEDTLS_ERR_READER_XXX error code on failure.
+ */
+int mbedtls_mps_reader_reclaim( mbedtls_mps_reader *reader,
+                                int *paused );
+
+/*
+ * Usage API (Upper layer)
+ */
+
+/**
+ * \brief           Request data from the reader.
+ *
+ * \param reader    The reader context to use. The reader must
+ *                  be in consuming mode.
+ * \param desired   The desired amount of data to be read, in Bytes.
+ * \param buffer    The address to store the buffer pointer in.
+ *                  This must not be \c NULL.
+ * \param buflen    The address to store the actual buffer
+ *                  length in, or \c NULL.
+ *
+ * \return          \c 0 on success. In this case, \c *buf holds the
+ *                  address of a buffer of size \c *buflen
+ *                  (if \c buflen != \c NULL) or \c desired
+ *                  (if \c buflen == \c NULL). The user has read access
+ *                  to the buffer and guarantee of stability of the data
+ *                  until the next call to mbedtls_mps_reader_reclaim().
+ * \return          #MBEDTLS_ERR_MPS_READER_OUT_OF_DATA if there is not enough
+ *                  data available to serve the get request. In this case, the
+ *                  reader remains intact and in consuming mode, and the consumer
+ *                  should retry the call after a successful cycle of
+ *                  mbedtls_mps_reader_reclaim() and mbedtls_mps_reader_feed().
+ *                  If, after such a cycle, the consumer requests a different
+ *                  amount of data, the result is implementation-defined;
+ *                  progress is guaranteed only if the same amount of data
+ *                  is requested after a mbedtls_mps_reader_reclaim() and
+ *                  mbedtls_mps_reader_feed() cycle.
+ * \return          Another negative \c MBEDTLS_ERR_READER_XXX error
+ *                  code for different kinds of failure.
+ *
+ * \note            Passing \c NULL as \p buflen is a convenient way to
+ *                  indicate that fragmentation is not tolerated.
+ *                  It's functionally equivalent to passing a valid
+ *                  address as buflen and checking \c *buflen == \c desired
+ *                  afterwards.
+ */
+int mbedtls_mps_reader_get( mbedtls_mps_reader *reader,
+                            mbedtls_mps_size_t desired,
+                            unsigned char **buffer,
+                            mbedtls_mps_size_t *buflen );
+
+/**
+ * \brief         Mark data obtained from mbedtls_mps_reader_get() as processed.
+ *
+ *                This call indicates that all data received from prior calls to
+ *                mbedtls_mps_reader_get() has been or will have been
+ *                processed when mbedtls_mps_reader_reclaim() is called,
+ *                and thus need not be backed up.
+ *
+ *                This function has no user observable effect until
+ *                mbedtls_mps_reader_reclaim() is called. In particular,
+ *                buffers received from mbedtls_mps_reader_get() remain
+ *                valid until mbedtls_mps_reader_reclaim() is called.
+ *
+ * \param reader  The reader context to use.
+ *
+ * \return        \c 0 on success.
+ * \return        A negative \c MBEDTLS_ERR_READER_XXX error code on failure.
+ *
+ */
+int mbedtls_mps_reader_commit( mbedtls_mps_reader *reader );
+
+#endif /* MBEDTLS_READER_H */
diff --git a/library/mps_trace.c b/library/mps_trace.c
new file mode 100644
index 0000000..dc0577d
--- /dev/null
+++ b/library/mps_trace.c
@@ -0,0 +1,127 @@
+/*
+ *  Message Processing Stack, Trace module
+ *
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of Mbed TLS (https://tls.mbed.org)
+ */
+
+#include "common.h"
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
+
+#include "mps_common.h"
+
+#if defined(MBEDTLS_MPS_ENABLE_TRACE)
+
+#include "mps_trace.h"
+#include <stdarg.h>
+
+static int trace_depth = 0;
+
+#define color_default  "\x1B[0m"
+#define color_red      "\x1B[1;31m"
+#define color_green    "\x1B[1;32m"
+#define color_yellow   "\x1B[1;33m"
+#define color_blue     "\x1B[1;34m"
+#define color_magenta  "\x1B[1;35m"
+#define color_cyan     "\x1B[1;36m"
+#define color_white    "\x1B[1;37m"
+
+static char const * colors[] =
+{
+    color_default,
+    color_green,
+    color_yellow,
+    color_magenta,
+    color_cyan,
+    color_blue,
+    color_white
+};
+
+#define MPS_TRACE_BUF_SIZE 100
+
+void mbedtls_mps_trace_print_msg( int id, int line, const char *format, ... )
+{
+    int ret;
+    char str[MPS_TRACE_BUF_SIZE];
+    va_list argp;
+    va_start( argp, format );
+    ret = mbedtls_vsnprintf( str, MPS_TRACE_BUF_SIZE, format, argp );
+    va_end( argp );
+
+    if( ret >= 0 && ret < MPS_TRACE_BUF_SIZE )
+    {
+        str[ret] = '\0';
+        mbedtls_printf( "[%d|L%d]: %s\n", id, line, str );
+    }
+}
+
+int mbedtls_mps_trace_get_depth()
+{
+    return trace_depth;
+}
+void mbedtls_mps_trace_dec_depth()
+{
+    trace_depth--;
+}
+void mbedtls_mps_trace_inc_depth()
+{
+    trace_depth++;
+}
+
+void mbedtls_mps_trace_color( int id )
+{
+    if( id > (int) ( sizeof( colors ) / sizeof( *colors ) ) )
+        return;
+    printf( "%s", colors[ id ] );
+}
+
+void mbedtls_mps_trace_indent( int level, mbedtls_mps_trace_type ty )
+{
+    if( level > 0 )
+    {
+        while( --level )
+            printf( "|  " );
+
+        printf( "|  " );
+    }
+
+    switch( ty )
+    {
+        case mbedtls_mps_trace_comment:
+            mbedtls_printf( "@ " );
+            break;
+
+        case mbedtls_mps_trace_call:
+            mbedtls_printf( "+--> " );
+            break;
+
+        case mbedtls_mps_trace_error:
+            mbedtls_printf( "E " );
+            break;
+
+        case mbedtls_mps_trace_return:
+            mbedtls_printf( "< " );
+            break;
+
+        default:
+            break;
+    }
+}
+
+#endif /* MBEDTLS_MPS_ENABLE_TRACE */
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
diff --git a/library/mps_trace.h b/library/mps_trace.h
new file mode 100644
index 0000000..048d573
--- /dev/null
+++ b/library/mps_trace.h
@@ -0,0 +1,175 @@
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+
+/**
+ * \file mps_trace.h
+ *
+ * \brief Tracing module for MPS
+ */
+
+#ifndef MBEDTLS_MPS_MBEDTLS_MPS_TRACE_H
+#define MBEDTLS_MPS_MBEDTLS_MPS_TRACE_H
+
+#include "common.h"
+#include "mps_common.h"
+#include "mps_trace.h"
+
+#if defined(MBEDTLS_PLATFORM_C)
+#include "mbedtls/platform.h"
+#else
+#include <stdio.h>
+#define mbedtls_printf    printf
+#define mbedtls_vsnprintf vsnprintf
+#endif /* MBEDTLS_PLATFORM_C */
+
+#if defined(MBEDTLS_MPS_ENABLE_TRACE)
+
+/*
+ * Adapt this to enable/disable tracing output
+ * from the various layers of the MPS.
+ */
+
+#define MBEDTLS_MPS_TRACE_ENABLE_LAYER_1
+#define MBEDTLS_MPS_TRACE_ENABLE_LAYER_2
+#define MBEDTLS_MPS_TRACE_ENABLE_LAYER_3
+#define MBEDTLS_MPS_TRACE_ENABLE_LAYER_4
+#define MBEDTLS_MPS_TRACE_ENABLE_READER
+#define MBEDTLS_MPS_TRACE_ENABLE_WRITER
+
+/*
+ * To use the existing trace module, only change
+ * MBEDTLS_MPS_TRACE_ENABLE_XXX above, but don't modify the
+ * rest of this file.
+ */
+
+typedef enum
+{
+    mbedtls_mps_trace_comment,
+    mbedtls_mps_trace_call,
+    mbedtls_mps_trace_error,
+    mbedtls_mps_trace_return
+} mbedtls_mps_trace_type;
+
+#define MBEDTLS_MPS_TRACE_BIT_LAYER_1 1
+#define MBEDTLS_MPS_TRACE_BIT_LAYER_2 2
+#define MBEDTLS_MPS_TRACE_BIT_LAYER_3 3
+#define MBEDTLS_MPS_TRACE_BIT_LAYER_4 4
+#define MBEDTLS_MPS_TRACE_BIT_WRITER  5
+#define MBEDTLS_MPS_TRACE_BIT_READER  6
+
+#if defined(MBEDTLS_MPS_TRACE_ENABLE_LAYER_1)
+#define MBEDTLS_MPS_TRACE_MASK_LAYER_1 (1u << MBEDTLS_MPS_TRACE_BIT_LAYER_1 )
+#else
+#define MBEDTLS_MPS_TRACE_MASK_LAYER_1 0
+#endif
+
+#if defined(MBEDTLS_MPS_TRACE_ENABLE_LAYER_2)
+#define MBEDTLS_MPS_TRACE_MASK_LAYER_2 (1u << MBEDTLS_MPS_TRACE_BIT_LAYER_2 )
+#else
+#define MBEDTLS_MPS_TRACE_MASK_LAYER_2 0
+#endif
+
+#if defined(MBEDTLS_MPS_TRACE_ENABLE_LAYER_3)
+#define MBEDTLS_MPS_TRACE_MASK_LAYER_3 (1u << MBEDTLS_MPS_TRACE_BIT_LAYER_3 )
+#else
+#define MBEDTLS_MPS_TRACE_MASK_LAYER_3 0
+#endif
+
+#if defined(MBEDTLS_MPS_TRACE_ENABLE_LAYER_4)
+#define MBEDTLS_MPS_TRACE_MASK_LAYER_4 (1u << MBEDTLS_MPS_TRACE_BIT_LAYER_4 )
+#else
+#define MBEDTLS_MPS_TRACE_MASK_LAYER_4 0
+#endif
+
+#if defined(MBEDTLS_MPS_TRACE_ENABLE_READER)
+#define MBEDTLS_MPS_TRACE_MASK_READER (1u << MBEDTLS_MPS_TRACE_BIT_READER )
+#else
+#define MBEDTLS_MPS_TRACE_MASK_READER 0
+#endif
+
+#if defined(MBEDTLS_MPS_TRACE_ENABLE_WRITER)
+#define MBEDTLS_MPS_TRACE_MASK_WRITER (1u << MBEDTLS_MPS_TRACE_BIT_WRITER )
+#else
+#define MBEDTLS_MPS_TRACE_MASK_WRITER 0
+#endif
+
+#define MBEDTLS_MPS_TRACE_MASK ( MBEDTLS_MPS_TRACE_MASK_LAYER_1 |       \
+                                 MBEDTLS_MPS_TRACE_MASK_LAYER_2 |       \
+                                 MBEDTLS_MPS_TRACE_MASK_LAYER_3 |       \
+                                 MBEDTLS_MPS_TRACE_MASK_LAYER_4 |       \
+                                 MBEDTLS_MPS_TRACE_MASK_READER  |       \
+                                 MBEDTLS_MPS_TRACE_MASK_WRITER )
+
+/* We have to avoid globals because E-ACSL chokes on them...
+ * Wrap everything in stub functions. */
+int  mbedtls_mps_trace_get_depth( void );
+void mbedtls_mps_trace_inc_depth( void );
+void mbedtls_mps_trace_dec_depth( void );
+
+void mbedtls_mps_trace_color( int id );
+void mbedtls_mps_trace_indent( int level, mbedtls_mps_trace_type ty );
+
+void mbedtls_mps_trace_print_msg( int id, int line, const char *format, ... );
+
+#define MBEDTLS_MPS_TRACE( type, ... )                                              \
+    do {                                                                            \
+        if( ! ( MBEDTLS_MPS_TRACE_MASK & ( 1u << mbedtls_mps_trace_id ) ) )         \
+            break;                                                                  \
+        mbedtls_mps_trace_indent( mbedtls_mps_trace_get_depth(), type );            \
+        mbedtls_mps_trace_color( mbedtls_mps_trace_id );                            \
+        mbedtls_mps_trace_print_msg( mbedtls_mps_trace_id, __LINE__, __VA_ARGS__ ); \
+        mbedtls_mps_trace_color( 0 );                                               \
+    } while( 0 )
+
+#define MBEDTLS_MPS_TRACE_INIT( ... )                                         \
+    do {                                                                      \
+        if( ! ( MBEDTLS_MPS_TRACE_MASK & ( 1u << mbedtls_mps_trace_id ) ) )   \
+            break;                                                            \
+        MBEDTLS_MPS_TRACE( mbedtls_mps_trace_call, __VA_ARGS__ );             \
+        mbedtls_mps_trace_inc_depth();                                        \
+    } while( 0 )
+
+#define MBEDTLS_MPS_TRACE_END( val )                                        \
+    do {                                                                    \
+        if( ! ( MBEDTLS_MPS_TRACE_MASK & ( 1u << mbedtls_mps_trace_id ) ) ) \
+            break;                                                          \
+        MBEDTLS_MPS_TRACE( mbedtls_mps_trace_return, "%d (-%#04x)",         \
+               (int) (val), -((unsigned)(val)) );                           \
+        mbedtls_mps_trace_dec_depth();                                      \
+    } while( 0 )
+
+#define MBEDTLS_MPS_TRACE_RETURN( val )         \
+    do {                                        \
+        /* Breaks tail recursion. */            \
+        int ret__ = val;                        \
+        MBEDTLS_MPS_TRACE_END( ret__ );         \
+        return( ret__ );                        \
+    } while( 0 )
+
+#else /* MBEDTLS_MPS_TRACE */
+
+#define MBEDTLS_MPS_TRACE( type, ... ) do { } while( 0 )
+#define MBEDTLS_MPS_TRACE_INIT( ... )  do { } while( 0 )
+#define MBEDTLS_MPS_TRACE_END          do { } while( 0 )
+
+#define MBEDTLS_MPS_TRACE_RETURN( val ) return( val );
+
+#endif /* MBEDTLS_MPS_TRACE */
+
+#endif /* MBEDTLS_MPS_MBEDTLS_MPS_TRACE_H */
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index c141704..049b130 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -134,6 +134,7 @@
 add_test_suite(mdx)
 add_test_suite(memory_buffer_alloc)
 add_test_suite(mpi)
+add_test_suite(mps)
 add_test_suite(net)
 add_test_suite(nist_kw)
 add_test_suite(oid)
diff --git a/tests/suites/test_suite_mps.data b/tests/suites/test_suite_mps.data
new file mode 100644
index 0000000..442f321
--- /dev/null
+++ b/tests/suites/test_suite_mps.data
@@ -0,0 +1,125 @@
+MPS Reader: Single step, single round, pausing disabled
+mbedtls_mps_reader_no_pausing_single_step_single_round:0
+
+MPS Reader: Single step, single round, pausing enabled but unused
+mbedtls_mps_reader_no_pausing_single_step_single_round:1
+
+MPS Reader: Single step, multiple rounds, pausing disabled
+mbedtls_mps_reader_no_pausing_single_step_multiple_rounds:0
+
+MPS Reader: Single step, multiple rounds, pausing enabled but unused
+mbedtls_mps_reader_no_pausing_single_step_multiple_rounds:1
+
+MPS Reader: Multiple steps, single round, pausing disabled
+mbedtls_mps_reader_no_pausing_multiple_steps_single_round:0
+
+MPS Reader: Multiple steps, single round, pausing enabled but unused
+mbedtls_mps_reader_no_pausing_multiple_steps_single_round:1
+
+MPS Reader: Multiple steps, multiple rounds, pausing disabled
+mbedtls_mps_reader_no_pausing_multiple_steps_multiple_rounds:0
+
+MPS Reader: Multiple steps, multiple rounds, pausing enabled but unused
+mbedtls_mps_reader_no_pausing_multiple_steps_multiple_rounds:1
+
+MPS Reader: Pausing needed but disabled
+mbedtls_mps_reader_pausing_needed_disabled:
+
+MPS Reader: Pausing needed + enabled, but buffer too small
+mbedtls_mps_reader_pausing_needed_buffer_too_small:
+
+MPS Reader: Pausing, repeat single call without commit
+mbedtls_mps_reader_pausing:0
+
+MPS Reader: Pausing, repeat single call with commit
+mbedtls_mps_reader_pausing:1
+
+MPS Reader: Pausing, repeat multiple calls without commit
+mbedtls_mps_reader_pausing:2
+
+MPS Reader: Pausing, repeat multiple calls with commit #0
+mbedtls_mps_reader_pausing:3
+
+MPS Reader: Pausing, repeat multiple calls with commit #1
+mbedtls_mps_reader_pausing:4
+
+MPS Reader: Pausing, repeat multiple calls with commit #2
+mbedtls_mps_reader_pausing:5
+
+MPS Reader: Pausing, feed 50 bytes in 10b + 10b + 80b
+mbedtls_mps_reader_pausing_multiple_feeds:0
+
+MPS Reader: Pausing, feed 50 bytes in 50x1b
+mbedtls_mps_reader_pausing_multiple_feeds:1
+
+MPS Reader: Pausing, feed 50 bytes in 49x1b + 51b
+mbedtls_mps_reader_pausing_multiple_feeds:2
+
+MPS Reader: Reclaim with data remaining #0
+mbedtls_mps_reader_reclaim_data_left:0
+
+MPS Reader: Reclaim with data remaining #1
+mbedtls_mps_reader_reclaim_data_left:1
+
+MPS Reader: Reclaim with data remaining #2
+mbedtls_mps_reader_reclaim_data_left:2
+
+MPS Reader: Reclaim with data remaining, continue fetching
+mbedtls_mps_reader_reclaim_data_left_retry:
+
+MPS Reader: Pausing several times, #0
+mbedtls_mps_reader_multiple_pausing:0
+
+MPS Reader: Pausing several times, #1
+mbedtls_mps_reader_multiple_pausing:1
+
+MPS Reader: Pausing several times, #2
+mbedtls_mps_reader_multiple_pausing:2
+
+MPS Reader: Pausing several times, #3
+mbedtls_mps_reader_multiple_pausing:3
+
+MPS Reader: Random usage, 20 rds, feed 100, get 200, acc 50
+mbedtls_mps_reader_random_usage:20:100:200:50
+
+MPS Reader: Random usage, 1000 rds, feed 10, get 100, acc 80
+mbedtls_mps_reader_random_usage:1000:10:100:80
+
+MPS Reader: Random usage, 10000 rds, feed 1, get 100, acc 80
+mbedtls_mps_reader_random_usage:10000:1:100:80
+
+MPS Reader: Random usage, 100 rds, feed 100, get 1000, acc 500
+mbedtls_mps_reader_random_usage:100:100:1000:500
+
+MPS Reader: Pausing, inconsistent continuation, #0
+mbedtls_reader_inconsistent_usage:0
+
+MPS Reader: Pausing, inconsistent continuation, #1
+mbedtls_reader_inconsistent_usage:1
+
+MPS Reader: Pausing, inconsistent continuation, #2
+mbedtls_reader_inconsistent_usage:2
+
+MPS Reader: Pausing, inconsistent continuation, #3
+mbedtls_reader_inconsistent_usage:3
+
+MPS Reader: Pausing, inconsistent continuation, #4
+mbedtls_reader_inconsistent_usage:4
+
+MPS Reader: Pausing, inconsistent continuation, #5
+mbedtls_reader_inconsistent_usage:5
+
+MPS Reader: Pausing, inconsistent continuation, #6
+mbedtls_reader_inconsistent_usage:6
+
+MPS Reader: Pausing, inconsistent continuation, #7
+mbedtls_reader_inconsistent_usage:7
+
+MPS Reader: Pausing, inconsistent continuation, #8
+mbedtls_reader_inconsistent_usage:8
+
+MPS Reader: Feed with invalid buffer (NULL)
+mbedtls_mps_reader_feed_empty:
+
+MPS Reader: Excess request leading to integer overflow
+mbedtls_mps_reader_reclaim_overflow:
diff --git a/tests/suites/test_suite_mps.function b/tests/suites/test_suite_mps.function
new file mode 100644
index 0000000..9df8a3c
--- /dev/null
+++ b/tests/suites/test_suite_mps.function
@@ -0,0 +1,1148 @@
+/* BEGIN_HEADER */
+
+#include <stdlib.h>
+
+#include "mps_reader.h"
+
+/*
+ * Compile-time configuration for test suite.
+ */
+
+/* Comment/Uncomment this to disable/enable the
+ * testing of the various MPS layers.
+ * This can be useful for time-consuming instrumentation
+ * tasks such as the conversion of E-ACSL annotations
+ * into runtime assertions. */
+#define TEST_SUITE_MPS_READER
+
+/* End of compile-time configuration. */
+
+/* END_HEADER */
+
+/* BEGIN_DEPENDENCIES
+ * depends_on:MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL
+ * END_DEPENDENCIES
+ */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_no_pausing_single_step_single_round( int with_acc )
+{
+    /* This test exercises the most basic use of the MPS reader:
+     * - The 'producing' layer provides a buffer
+     * - The 'consuming' layer fetches it in a single go.
+     * - After processing, the consuming layer commits the data
+     *   and the reader is moved back to producing mode.
+     *
+     * Parameters:
+     * - with_acc: 0 if the reader should be initialized without accumulator.
+     *             1 if the reader should be initialized with accumulator.
+     *
+     *             Whether the accumulator is present or not should not matter,
+     *             since the consumer's request can be fulfilled from the data
+     *             that the producer has provided.
+     */
+    unsigned char bufA[100];
+    unsigned char acc[10];
+    unsigned char *tmp;
+    int paused;
+    mbedtls_mps_reader rd;
+    for( size_t i=0; (unsigned) i < sizeof( bufA ); i++ )
+        bufA[i] = (unsigned char) i;
+
+    /* Preparation (lower layer) */
+    if( with_acc == 0 )
+        mbedtls_mps_reader_init( &rd, NULL, 0 );
+    else
+        mbedtls_mps_reader_init( &rd, acc, sizeof( acc ) );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufA, sizeof( bufA ) ) == 0 );
+    /* Consumption (upper layer) */
+    /* Consume exactly what's available */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 100, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 100, bufA, 100 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    /* Wrapup (lower layer) */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, &paused ) == 0 );
+    TEST_ASSERT( paused == 0 );
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_no_pausing_single_step_multiple_rounds( int with_acc )
+{
+    /* This test exercises multiple rounds of the basic use of the MPS reader:
+     * - The 'producing' layer provides a buffer
+     * - The 'consuming' layer fetches it in a single go.
+     * - After processing, the consuming layer commits the data
+     *   and the reader is moved back to producing mode.
+     *
+     * Parameters:
+     * - with_acc: 0 if the reader should be initialized without accumulator.
+     *             1 if the reader should be initialized with accumulator.
+     *
+     *             Whether the accumulator is present or not should not matter,
+     *             since the consumer's request can be fulfilled from the data
+     *             that the producer has provided.
+     */
+
+    unsigned char bufA[100], bufB[100];
+    unsigned char acc[10];
+    unsigned char *tmp;
+    mbedtls_mps_reader rd;
+    for( size_t i=0; (unsigned) i < sizeof( bufA ); i++ )
+        bufA[i] = (unsigned char) i;
+    for( size_t i=0; (unsigned) i < sizeof( bufB ); i++ )
+        bufB[i] = ~ ((unsigned char) i);
+
+    /* Preparation (lower layer) */
+    if( with_acc == 0 )
+        mbedtls_mps_reader_init( &rd, NULL, 0 );
+    else
+        mbedtls_mps_reader_init( &rd, acc, sizeof( acc ) );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufA, sizeof( bufA ) ) == 0 );
+    /* Consumption (upper layer) */
+    /* Consume exactly what's available */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 100, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 100, bufA, 100 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    /* Preparation */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB, sizeof( bufB ) ) == 0 );
+    /* Consumption */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 100, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 100, bufB, 100 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    /* Wrapup (lower layer) */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_no_pausing_multiple_steps_single_round( int with_acc )
+{
+    /* This test exercises one round of the following:
+     * - The 'producing' layer provides a buffer
+     * - The 'consuming' layer fetches it in multiple calls
+     *   to `mbedtls_mps_reader_get()`, without committing in between.
+     * - After processing, the consuming layer commits the data
+     *   and the reader is moved back to producing mode.
+     *
+     * Parameters:
+     * - with_acc: 0 if the reader should be initialized without accumulator.
+     *             1 if the reader should be initialized with accumulator.
+     *
+     *             Whether the accumulator is present or not should not matter,
+     *             since the consumer's requests can be fulfilled from the data
+     *             that the producer has provided.
+     */
+
+    /* Lower layer provides data that the upper layer fully consumes
+     * through multiple `get` calls. */
+    unsigned char buf[100];
+    unsigned char acc[10];
+    unsigned char *tmp;
+    mbedtls_mps_size_t tmp_len;
+    mbedtls_mps_reader rd;
+    for( size_t i=0; (unsigned) i < sizeof( buf ); i++ )
+        buf[i] = (unsigned char) i;
+
+    /* Preparation (lower layer) */
+    if( with_acc == 0 )
+        mbedtls_mps_reader_init( &rd, NULL, 0 );
+    else
+        mbedtls_mps_reader_init( &rd, acc, sizeof( acc ) );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, buf, sizeof( buf ) ) == 0 );
+    /* Consumption (upper layer) */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 10, buf, 10 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 70, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 70, buf + 10, 70 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 30, &tmp, &tmp_len ) == 0 );
+    ASSERT_COMPARE( tmp, tmp_len, buf + 80, 20 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    /* Wrapup (lower layer) */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_no_pausing_multiple_steps_multiple_rounds( int with_acc )
+{
+    /* This test exercises one round of fetching a buffer in multiple chunks
+     * and passing it back to the producer afterwards, followed by another
+     * single-step sequence of feed-fetch-commit-reclaim.
+     */
+    unsigned char bufA[100], bufB[100];
+    unsigned char acc[10];
+    unsigned char *tmp;
+    mbedtls_mps_size_t tmp_len;
+    mbedtls_mps_reader rd;
+    for( size_t i=0; (unsigned) i < sizeof( bufA ); i++ )
+        bufA[i] = (unsigned char) i;
+    for( size_t i=0; (unsigned) i < sizeof( bufB ); i++ )
+        bufB[i] = ~ ((unsigned char) i);
+
+    /* Preparation (lower layer) */
+    if( with_acc == 0 )
+        mbedtls_mps_reader_init( &rd, NULL, 0 );
+    else
+        mbedtls_mps_reader_init( &rd, acc, sizeof( acc ) );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufA, sizeof( bufA ) ) == 0 );
+    /* Consumption (upper layer) */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 10, bufA, 10 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 70, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 70, bufA + 10, 70 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 30, &tmp, &tmp_len ) == 0 );
+    ASSERT_COMPARE( tmp, tmp_len, bufA + 80, 20 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    /* Preparation */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB, sizeof( bufB ) ) == 0 );
+    /* Consumption */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 100, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 100, bufB, 100 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    /* Wrapup */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_pausing_needed_disabled()
+{
+    /* This test exercises the behaviour of the MPS reader when a read request
+     * of the consumer exceeds what has been provided by the producer, and when
+     * no accumulator is available in the reader.
+     *
+     * In this case, we expect the reader to fail.
+     */
+
+    unsigned char buf[100];
+    unsigned char *tmp;
+    mbedtls_mps_reader rd;
+    for( size_t i=0; (unsigned) i < sizeof( buf ); i++ )
+        buf[i] = (unsigned char) i;
+
+    /* Preparation (lower layer) */
+    mbedtls_mps_reader_init( &rd, NULL, 0 );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, buf, sizeof( buf ) ) == 0 );
+    /* Consumption (upper layer) */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 50, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 50, buf, 50 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 100, &tmp, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+    /* Wrapup (lower layer) */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_NEED_ACCUMULATOR );
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_pausing_needed_buffer_too_small()
+{
+    /* This test exercises the behaviour of the MPS reader with accumulator
+     * in the situation where a read request goes beyond the bounds of the
+     * current read buffer, _and_ the reader's accumulator is too small to
+     * hold the requested amount of data.
+     *
+     * In this case, we expect mbedtls_mps_reader_reclaim() to fail,
+     * but it should be possible to continue fetching data as if
+     * there had been no excess request via mbedtls_mps_reader_get()
+     * and the call to mbedtls_mps_reader_reclaim() had been rejected
+     * because of data remaining.
+     */
+
+    unsigned char buf[100];
+    unsigned char acc[10];
+    unsigned char *tmp;
+    mbedtls_mps_reader rd;
+    mbedtls_mps_size_t tmp_len;
+
+    for( size_t i=0; (unsigned) i < sizeof( buf ); i++ )
+        buf[i] = (unsigned char) i;
+
+    /* Preparation (lower layer) */
+    mbedtls_mps_reader_init( &rd, acc, sizeof( acc ) );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, buf, sizeof( buf ) ) == 0 );
+    /* Consumption (upper layer) */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 50, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 50, buf, 50 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 10, buf + 50, 10 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 100, &tmp, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+    /* Wrapup (lower layer) */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_ACCUMULATOR_TOO_SMALL );
+
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 50, &tmp, &tmp_len ) == 0 );
+    ASSERT_COMPARE( tmp, tmp_len, buf + 50, 50 );
+
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_reclaim_overflow()
+{
+    /* This test exercises the behaviour of the MPS reader with accumulator
+     * in the situation where upon calling mbedtls_mps_reader_reclaim(), the
+     * uncommitted data together with the excess data missing in the last
+     * call to medtls_mps_reader_get() exceeds the bounds of the type
+     * holding the buffer length.
+     */
+
+    unsigned char buf[100];
+    unsigned char acc[50];
+    unsigned char *tmp;
+    mbedtls_mps_reader rd;
+
+    for( size_t i=0; (unsigned) i < sizeof( buf ); i++ )
+        buf[i] = (unsigned char) i;
+
+    /* Preparation (lower layer) */
+    mbedtls_mps_reader_init( &rd, acc, sizeof( acc ) );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, buf, sizeof( buf ) ) == 0 );
+    /* Consumption (upper layer) */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 50, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 50, buf, 50 );
+    /* Excess request */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, (mbedtls_mps_size_t) -1, &tmp, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+    /* Wrapup (lower layer) */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_ACCUMULATOR_TOO_SMALL );
+
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_pausing( int option )
+{
+    /* This test exercises the behaviour of the reader when the
+     * accumulator is used to fulfill a consumer's request.
+     *
+     * More detailed:
+     * - The producer feeds some data.
+     * - The consumer asks for more data than what's available.
+     * - The reader remembers the request and goes back to
+     *   producing mode, waiting for more data from the producer.
+     * - The producer provides another chunk of data which is
+     *   sufficient to fulfill the original read request.
+     * - The consumer retries the original read request, which
+     *   should now succeed.
+     *
+     * This test comes in multiple variants controlled by the
+     * `option` parameter and documented below.
+     */
+
+    unsigned char bufA[100], bufB[100];
+    unsigned char *tmp;
+    unsigned char acc[40];
+    int paused;
+    mbedtls_mps_reader rd;
+    for( size_t i=0; (unsigned) i < sizeof( bufA ); i++ )
+        bufA[i] = (unsigned char) i;
+    for( size_t i=0; (unsigned) i < sizeof( bufB ); i++ )
+        bufB[i] = ~ ((unsigned char) i);
+
+    /* Preparation (lower layer) */
+    mbedtls_mps_reader_init( &rd, acc, sizeof( acc ) );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufA, sizeof( bufA ) ) == 0 );
+
+    /* Consumption (upper layer) */
+    /* Ask for more than what's available. */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 80, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 80, bufA, 80 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 10, bufA + 80, 10 );
+    switch( option )
+    {
+        case 0:  /* Single uncommitted fetch at pausing */
+        case 1:
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            break;
+        default: /* Multiple uncommitted fetches at pausing */
+            break;
+    }
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+
+    /* Preparation */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, &paused ) == 0 );
+    TEST_ASSERT( paused == 1 );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB, sizeof( bufB ) ) == 0 );
+
+    /* Consumption */
+    switch( option )
+    {
+        case 0: /* Single fetch at pausing, re-fetch with commit. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 90, 10 );
+            ASSERT_COMPARE( tmp + 10, 10, bufB, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            break;
+
+        case 1: /* Single fetch at pausing, re-fetch without commit. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 90, 10 );
+            ASSERT_COMPARE( tmp + 10, 10, bufB, 10 );
+            break;
+
+        case 2: /* Multiple fetches at pausing, repeat without commit. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 80, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 90, 10 );
+            ASSERT_COMPARE( tmp + 10, 10, bufB, 10 );
+            break;
+
+        case 3: /* Multiple fetches at pausing, repeat with commit 1. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 80, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 90, 10 );
+            ASSERT_COMPARE( tmp + 10, 10, bufB, 10 );
+            break;
+
+        case 4: /* Multiple fetches at pausing, repeat with commit 2. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 80, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 90, 10 );
+            ASSERT_COMPARE( tmp + 10, 10, bufB, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            break;
+
+        case 5: /* Multiple fetches at pausing, repeat with commit 3. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 80, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 90, 10 );
+            ASSERT_COMPARE( tmp + 10, 10, bufB, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            break;
+
+        default:
+            TEST_ASSERT( 0 );
+    }
+
+    /* In all cases, fetch the rest of the second buffer. */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 90, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 90, bufB + 10, 90 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+
+    /* Wrapup */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_pausing_multiple_feeds( int option )
+{
+    /* This test exercises the behaviour of the MPS reader
+     * in the following situation:
+     * - The consumer has asked for more than what's available, so the
+     *   reader pauses and waits for further input data via
+     *   `mbedtls_mps_reader_feed()`
+     * - Multiple such calls to `mbedtls_mps_reader_feed()` are necessary
+     *   to fulfill the original request, and the reader needs to do
+     *   the necessary bookkeeping under the hood.
+     *
+     * This test comes in a few variants differing in the number and
+     * size of feed calls that the producer issues while the reader is
+     * accumulating the necessary data - see the comments below.
+     */
+
+    unsigned char bufA[100], bufB[100];
+    unsigned char *tmp;
+    unsigned char acc[70];
+    mbedtls_mps_reader rd;
+    mbedtls_mps_size_t fetch_len;
+    for( size_t i=0; (unsigned) i < sizeof( bufA ); i++ )
+        bufA[i] = (unsigned char) i;
+    for( size_t i=0; (unsigned) i < sizeof( bufB ); i++ )
+        bufB[i] = ~ ((unsigned char) i);
+
+    /* Preparation (lower layer) */
+    mbedtls_mps_reader_init( &rd, acc, sizeof( acc ) );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufA, sizeof( bufA ) ) == 0 );
+
+    /* Consumption (upper layer) */
+    /* Ask for more than what's available. */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 80, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 80, bufA, 80 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    /* 20 left, ask for 70 -> 50 overhead */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 70, &tmp, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+
+    /* Preparation */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    switch( option )
+    {
+        case 0: /* 10 + 10 + 80 byte feed */
+            TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB, 10 ) ==
+                         MBEDTLS_ERR_MPS_READER_NEED_MORE );
+            TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB + 10, 10 ) ==
+                         MBEDTLS_ERR_MPS_READER_NEED_MORE );
+            TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB + 20, 80 ) == 0 );
+            break;
+
+        case 1: /* 50 x 1byte */
+            for( size_t num_feed = 0; num_feed < 49; num_feed++ )
+            {
+                TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB + num_feed, 1 ) ==
+                             MBEDTLS_ERR_MPS_READER_NEED_MORE );
+            }
+            TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB + 49, 1 ) == 0 );
+            break;
+
+        case 2: /* 49 x 1byte + 51bytes */
+            for( size_t num_feed = 0; num_feed < 49; num_feed++ )
+            {
+                TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB + num_feed, 1 ) ==
+                             MBEDTLS_ERR_MPS_READER_NEED_MORE );
+            }
+            TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB + 49, 51 ) == 0 );
+            break;
+
+        default:
+            TEST_ASSERT( 0 );
+            break;
+    }
+
+    /* Consumption */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 70, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 20, bufA + 80, 20 );
+    ASSERT_COMPARE( tmp + 20, 50, bufB, 50 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 1000, &tmp, &fetch_len ) == 0 );
+    switch( option )
+    {
+        case 0:
+            TEST_ASSERT( fetch_len == 50 );
+            break;
+
+        case 1:
+            TEST_ASSERT( fetch_len == 0 );
+            break;
+
+        case 2:
+            TEST_ASSERT( fetch_len == 50 );
+            break;
+
+        default:
+            TEST_ASSERT( 0 );
+            break;
+    }
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+
+    /* Wrapup */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_reclaim_data_left( int option )
+{
+    /* This test exercises the behaviour of the MPS reader when a
+     * call to mbedtls_mps_reader_reclaim() is made before all data
+     * provided by the producer has been fetched and committed. */
+
+    unsigned char buf[100];
+    unsigned char *tmp;
+    mbedtls_mps_reader rd;
+    for( size_t i=0; (unsigned) i < sizeof( buf ); i++ )
+        buf[i] = (unsigned char) i;
+
+    /* Preparation (lower layer) */
+    mbedtls_mps_reader_init( &rd, NULL, 0 );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, buf, sizeof( buf ) ) == 0 );
+
+    /* Consumption (upper layer) */
+    switch( option )
+    {
+        case 0:
+            /* Fetch (but not commit) the entire buffer. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, sizeof( buf ), &tmp, NULL )
+                         == 0 );
+            ASSERT_COMPARE( tmp, 100, buf, 100 );
+            break;
+
+        case 1:
+            /* Fetch (but not commit) parts of the buffer. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, sizeof( buf ) / 2,
+                                             &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, sizeof( buf ) / 2, buf, sizeof( buf ) / 2 );
+            break;
+
+        case 2:
+            /* Fetch and commit parts of the buffer, then
+             * fetch but not commit the rest of the buffer. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, sizeof( buf ) / 2,
+                                             &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, sizeof( buf ) / 2, buf, sizeof( buf ) / 2 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, sizeof( buf ) / 2,
+                                             &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, sizeof( buf ) / 2,
+                            buf + sizeof( buf ) / 2,
+                            sizeof( buf ) / 2 );
+            break;
+
+        default:
+            TEST_ASSERT( 0 );
+            break;
+    }
+
+    /* Wrapup */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_DATA_LEFT );
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_reclaim_data_left_retry()
+{
+    /* This test exercises the behaviour of the MPS reader when an attempt
+     * by the producer to reclaim the reader fails because of more data pending
+     * to be processed, and the consumer subsequently fetches more data. */
+    unsigned char buf[100];
+    unsigned char *tmp;
+    mbedtls_mps_reader rd;
+
+    for( size_t i=0; (unsigned) i < sizeof( buf ); i++ )
+        buf[i] = (unsigned char) i;
+
+    /* Preparation (lower layer) */
+    mbedtls_mps_reader_init( &rd, NULL, 0 );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, buf, sizeof( buf ) ) == 0 );
+    /* Consumption (upper layer) */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 50, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 50, buf, 50 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 50, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 50, buf + 50, 50 );
+    /* Preparation */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_DATA_LEFT );
+    /* Consumption */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 50, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 50, buf + 50, 50 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    /* Wrapup */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_multiple_pausing( int option )
+{
+    /* This test exercises the behaviour of the MPS reader
+     * in the following situation:
+     * - A read request via `mbedtls_mps_reader_get()` can't
+     *   be served and the reader is paused to accumulate
+     *   the desired amount of data from the producer.
+     * - Once enough data is available, the consumer successfully
+     *   reads the data from the reader, but afterwards exceeds
+     *   the available data again - pausing is necessary for a
+     *   second time.
+     */
+
+    unsigned char bufA[100], bufB[20], bufC[10];
+    unsigned char *tmp;
+    unsigned char acc[50];
+    mbedtls_mps_size_t tmp_len;
+    mbedtls_mps_reader rd;
+    for( size_t i=0; (unsigned) i < sizeof( bufA ); i++ )
+        bufA[i] = (unsigned char) i;
+    for( size_t i=0; (unsigned) i < sizeof( bufB ); i++ )
+        bufB[i] = ~ ((unsigned char) i);
+    for( size_t i=0; (unsigned) i < sizeof( bufC ); i++ )
+        bufC[i] = ~ ((unsigned char) i);
+
+    /* Preparation (lower layer) */
+    mbedtls_mps_reader_init( &rd, acc, sizeof( acc ) );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufA, sizeof( bufA ) ) == 0 );
+
+    /* Consumption (upper layer) */
+    /* Ask for more than what's available. */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 80, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 80, bufA, 80 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 10, bufA + 80, 10 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+
+    /* Preparation */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB, sizeof( bufB ) ) == 0 );
+
+    switch( option )
+    {
+        case 0: /* Fetch same chunks, commit afterwards, and
+                 * then exceed bounds of new buffer; accumulator
+                 * large enough. */
+
+            /* Consume */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, &tmp_len ) == 0 );
+            ASSERT_COMPARE( tmp, tmp_len, bufA + 80, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 90, 10 );
+            ASSERT_COMPARE( tmp + 10, 10, bufB, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) ==
+                         MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+
+            /* Prepare */
+            TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+            TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufC, sizeof( bufC ) ) == 0 );;
+
+            /* Consume */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufB + 10, 10 );
+            ASSERT_COMPARE( tmp + 10, 10, bufC, 10 );
+            break;
+
+        case 1: /* Fetch same chunks, commit afterwards, and
+                 * then exceed bounds of new buffer; accumulator
+                 * not large enough. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 80, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 90, 10 );
+            ASSERT_COMPARE( tmp + 10, 10, bufB, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 51, &tmp, NULL ) ==
+                         MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+
+            /* Prepare */
+            TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) ==
+                         MBEDTLS_ERR_MPS_READER_ACCUMULATOR_TOO_SMALL );
+            break;
+
+        case 2: /* Fetch same chunks, don't commit afterwards, and
+                 * then exceed bounds of new buffer; accumulator
+                 * large enough. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 80, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 90, 10 );
+            ASSERT_COMPARE( tmp + 10, 10, bufB, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) ==
+                         MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+
+            /* Prepare */
+            TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+            TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufC, sizeof( bufC ) ) == 0 );;
+
+            /* Consume */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 50, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 20, bufA + 80, 20 );
+            ASSERT_COMPARE( tmp + 20, 20, bufB, 20 );
+            ASSERT_COMPARE( tmp + 40, 10, bufC, 10 );
+            break;
+
+        case 3: /* Fetch same chunks, don't commit afterwards, and
+                 * then exceed bounds of new buffer; accumulator
+                 * not large enough. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 80, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 10, bufA + 90, 10 );
+            ASSERT_COMPARE( tmp + 10, 10, bufB, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 21, &tmp, NULL ) ==
+                         MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+
+            /* Prepare */
+            TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) ==
+                         MBEDTLS_ERR_MPS_READER_ACCUMULATOR_TOO_SMALL );
+            break;
+
+        default:
+            TEST_ASSERT( 0 );
+            break;
+    }
+
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER:MBEDTLS_MPS_STATE_VALIDATION */
+void mbedtls_mps_reader_random_usage( int num_out_chunks,
+                                      int max_chunk_size,
+                                      int max_request,
+                                      int acc_size )
+
+{
+    /* Randomly pass a reader object back and forth between lower and
+     * upper layer and let each of them call the respective reader API
+     * functions in a random fashion.
+     *
+     * On the lower layer, we're tracking and concatenating
+     * the data passed to successful feed calls.
+     *
+     * For the upper layer, we track and concatenate buffers
+     * obtained from successful get calls.
+     *
+     * As long as the lower layer calls reclaim at least once, (resetting the
+     * fetched but not-yet-committed data), this should always lead to the same
+     * stream of outgoing/incoming data for the lower/upper layers, even if
+     * most of the random calls fail.
+     *
+     * NOTE: This test uses rand() for random data, which is not optimal.
+     *       Instead, it would be better to get the random data from a
+     *       static buffer. This both eases reproducibility and allows
+     *       simple conversion to a fuzz target.
+     */
+    int ret;
+    unsigned char *acc = NULL;
+    unsigned char *outgoing = NULL, *incoming = NULL;
+    unsigned char *cur_chunk = NULL;
+    size_t cur_out_chunk, out_pos, in_commit, in_fetch;
+    int rand_op;  /* Lower layer:
+                   * - Reclaim (0)
+                   * - Feed (1)
+                   * Upper layer:
+                   * - Get, do tolerate smaller output (0)
+                   * - Get, don't tolerate smaller output (1)
+                   * - Commit (2) */
+    int mode = 0; /* Lower layer (0) or Upper layer (1) */
+    int reclaimed = 1; /* Have to call reclaim at least once before
+                        * returning the reader to the upper layer. */
+    mbedtls_mps_reader rd;
+
+    if( acc_size > 0 )
+    {
+        ASSERT_ALLOC( acc, acc_size );
+    }
+
+    /* This probably needs to be changed because we want
+     * our tests to be deterministic. */
+    //    srand( time( NULL ) );
+
+    ASSERT_ALLOC( outgoing, num_out_chunks * max_chunk_size );
+    ASSERT_ALLOC( incoming, num_out_chunks * max_chunk_size );
+
+    mbedtls_mps_reader_init( &rd, acc, acc_size );
+
+    cur_out_chunk = 0;
+    in_commit = 0;
+    in_fetch = 0;
+    out_pos = 0;
+    while( cur_out_chunk < (unsigned) num_out_chunks )
+    {
+        if( mode == 0 )
+        {
+            /* Choose randomly between reclaim and feed */
+            rand_op = rand() % 2;
+
+            if( rand_op == 0 )
+            {
+                /* Reclaim */
+                ret = mbedtls_mps_reader_reclaim( &rd, NULL );
+
+                if( ret == 0 )
+                {
+                    TEST_ASSERT( cur_chunk != NULL );
+                    mbedtls_free( cur_chunk );
+                    cur_chunk = NULL;
+                }
+                reclaimed = 1;
+            }
+            else
+            {
+                /* Feed reader with a random chunk */
+                unsigned char *tmp = NULL;
+                size_t tmp_size;
+                if( cur_out_chunk == (unsigned) num_out_chunks )
+                    continue;
+
+                tmp_size = ( rand() % max_chunk_size ) + 1;
+                ASSERT_ALLOC( tmp, tmp_size );
+
+                TEST_ASSERT( mbedtls_test_rnd_std_rand( NULL, tmp, tmp_size ) == 0 );
+                ret = mbedtls_mps_reader_feed( &rd, tmp, tmp_size );
+
+                if( ret == 0 || ret == MBEDTLS_ERR_MPS_READER_NEED_MORE )
+                {
+                    cur_out_chunk++;
+                    memcpy( outgoing + out_pos, tmp, tmp_size );
+                    out_pos += tmp_size;
+                }
+
+                if( ret == 0 )
+                {
+                    TEST_ASSERT( cur_chunk == NULL );
+                    cur_chunk = tmp;
+                }
+                else
+                {
+                    mbedtls_free( tmp );
+                }
+
+            }
+
+            /* Randomly switch to consumption mode if reclaim
+             * was called at least once. */
+            if( reclaimed == 1 && rand() % 3 == 0 )
+            {
+                in_fetch = 0;
+                mode = 1;
+            }
+        }
+        else
+        {
+            /* Choose randomly between get tolerating fewer data,
+             * get not tolerating fewer data, and commit. */
+            rand_op = rand() % 3;
+            if( rand_op == 0 || rand_op == 1 )
+            {
+                mbedtls_mps_size_t get_size, real_size;
+                unsigned char *chunk_get;
+                get_size = ( rand() % max_request ) + 1;
+                if( rand_op == 0 )
+                {
+                    ret = mbedtls_mps_reader_get( &rd, get_size, &chunk_get,
+                                              &real_size );
+                }
+                else
+                {
+                    real_size = get_size;
+                    ret = mbedtls_mps_reader_get( &rd, get_size, &chunk_get, NULL );
+                }
+
+                /* Check if output is in accordance with what was written */
+                if( ret == 0 )
+                {
+                    memcpy( incoming + in_commit + in_fetch,
+                            chunk_get, real_size );
+                    TEST_ASSERT( memcmp( incoming + in_commit + in_fetch,
+                                         outgoing + in_commit + in_fetch,
+                                         real_size ) == 0 );
+                    in_fetch += real_size;
+                }
+            }
+            else if( rand_op == 2 ) /* Commit */
+            {
+                ret = mbedtls_mps_reader_commit( &rd );
+                if( ret == 0 )
+                {
+                    in_commit += in_fetch;
+                    in_fetch = 0;
+                }
+            }
+
+            /* Randomly switch back to preparation */
+            if( rand() % 3 == 0 )
+            {
+                reclaimed = 0;
+                mode = 0;
+            }
+        }
+    }
+
+    /* Cleanup */
+    mbedtls_mps_reader_free( &rd );
+    mbedtls_free( incoming );
+    mbedtls_free( outgoing );
+    mbedtls_free( acc );
+    mbedtls_free( cur_chunk );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_reader_inconsistent_usage( int option )
+{
+    /* This test exercises the behaviour of the MPS reader
+     * in the following situation:
+     * - The consumer asks for more data than what's available
+     * - The reader is paused and receives more data from the
+     *   producer until the original read request can be fulfilled.
+     * - The consumer does not repeat the original request but
+     *   requests data in a different way.
+     *
+     * The reader does not guarantee that inconsistent read requests
+     * after pausing will succeed, and this test triggers some cases
+     * where the request fails.
+     */
+
+    unsigned char bufA[100], bufB[100];
+    unsigned char *tmp;
+    unsigned char acc[40];
+    mbedtls_mps_reader rd;
+    int success = 0;
+    for( size_t i=0; (unsigned) i < sizeof( bufA ); i++ )
+        bufA[i] = (unsigned char) i;
+    for( size_t i=0; (unsigned) i < sizeof( bufB ); i++ )
+        bufB[i] = ~ ((unsigned char) i);
+
+    /* Preparation (lower layer) */
+    mbedtls_mps_reader_init( &rd, acc, sizeof( acc ) );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufA, sizeof( bufA ) ) == 0 );
+    /* Consumption (upper layer) */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 80, &tmp, NULL ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 20, &tmp, NULL ) ==
+                 MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
+    /* Preparation */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, bufB, sizeof( bufB ) ) == 0 );
+    /* Consumption */
+    switch( option )
+    {
+        case 0:
+            /* Ask for buffered data in a single chunk, no commit */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 30, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 20, bufA + 80, 20 );
+            ASSERT_COMPARE( tmp + 20, 10, bufB, 10 );
+            success = 1;
+            break;
+
+        case 1:
+            /* Ask for buffered data in a single chunk, with commit */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 30, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 20, bufA + 80, 20 );
+            ASSERT_COMPARE( tmp + 20, 10, bufB, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            success = 1;
+            break;
+
+        case 2:
+            /* Ask for more than was requested when pausing, #1 */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 31, &tmp, NULL ) ==
+                         MBEDTLS_ERR_MPS_READER_INCONSISTENT_REQUESTS );
+            break;
+
+        case 3:
+            /* Ask for more than was requested when pausing #2 */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, (mbedtls_mps_size_t) -1, &tmp, NULL ) ==
+                         MBEDTLS_ERR_MPS_READER_INCONSISTENT_REQUESTS );
+            break;
+
+        case 4:
+            /* Asking for buffered data in different
+             * chunks than before CAN fail. */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 15, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 15, bufA + 80, 15 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 10, &tmp, NULL ) ==
+                         MBEDTLS_ERR_MPS_READER_INCONSISTENT_REQUESTS );
+            break;
+
+        case 5:
+            /* Asking for buffered data different chunks
+             * than before NEED NOT fail - no commits */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 15, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 15, bufA + 80, 15 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 15, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 5, bufA + 95, 5 );
+            ASSERT_COMPARE( tmp + 5, 10, bufB, 10 );
+            success = 1;
+            break;
+
+        case 6:
+            /* Asking for buffered data different chunks
+             * than before NEED NOT fail - intermediate commit */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 15, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 15, bufA + 80, 15 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 15, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 5, bufA + 95, 5 );
+            ASSERT_COMPARE( tmp + 5, 10, bufB, 10 );
+            success = 1;
+            break;
+
+        case 7:
+            /* Asking for buffered data different chunks
+             * than before NEED NOT fail - end commit */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 15, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 15, bufA + 80, 15 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 15, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 5, bufA + 95, 5 );
+            ASSERT_COMPARE( tmp + 5, 10, bufB, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            success = 1;
+            break;
+
+        case 8:
+            /* Asking for buffered data different chunks
+             * than before NEED NOT fail - intermediate & end commit */
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 15, &tmp, NULL ) == 0 );
+            ASSERT_COMPARE( tmp, 15, bufA + 80, 15 );
+            TEST_ASSERT( mbedtls_mps_reader_get( &rd, 15, &tmp, NULL ) == 0 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            ASSERT_COMPARE( tmp, 5, bufA + 95, 5 );
+            ASSERT_COMPARE( tmp + 5, 10, bufB, 10 );
+            TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+            success = 1;
+            break;
+
+        default:
+            TEST_ASSERT( 0 );
+            break;
+    }
+
+    if( success == 1 )
+    {
+        /* In all succeeding cases, fetch the rest of the second buffer. */
+        TEST_ASSERT( mbedtls_mps_reader_get( &rd, 90, &tmp, NULL ) == 0 );
+        ASSERT_COMPARE( tmp, 90, bufB + 10, 90 );
+        TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+
+        /* Wrapup */
+        TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    }
+
+    /* Wrapup */
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:TEST_SUITE_MPS_READER */
+void mbedtls_mps_reader_feed_empty()
+{
+    /* This test exercises the behaviour of the reader when it is
+     * fed with a NULL buffer. */
+    unsigned char buf[100];
+    unsigned char *tmp;
+    mbedtls_mps_reader rd;
+    for( size_t i=0; (unsigned) i < sizeof( buf ); i++ )
+        buf[i] = (unsigned char) i;
+
+    /* Preparation (lower layer) */
+    mbedtls_mps_reader_init( &rd, NULL, 0 );
+
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, NULL, sizeof( buf ) ) ==
+                 MBEDTLS_ERR_MPS_READER_INVALID_ARG );
+
+    /* Subsequent feed-calls should still succeed. */
+    TEST_ASSERT( mbedtls_mps_reader_feed( &rd, buf, sizeof( buf ) ) == 0 );
+
+    /* Consumption (upper layer) */
+    TEST_ASSERT( mbedtls_mps_reader_get( &rd, 100, &tmp, NULL ) == 0 );
+    ASSERT_COMPARE( tmp, 100, buf, 100 );
+    TEST_ASSERT( mbedtls_mps_reader_commit( &rd ) == 0 );
+
+    /* Wrapup */
+    TEST_ASSERT( mbedtls_mps_reader_reclaim( &rd, NULL ) == 0 );
+    mbedtls_mps_reader_free( &rd );
+}
+/* END_CASE */
diff --git a/visualc/VS2010/mbedTLS.vcxproj b/visualc/VS2010/mbedTLS.vcxproj
index 0fb1b5c..09c5341 100644
--- a/visualc/VS2010/mbedTLS.vcxproj
+++ b/visualc/VS2010/mbedTLS.vcxproj
@@ -251,6 +251,10 @@
     <ClInclude Include="..\..\tests\include\test\drivers\test_driver.h" />

     <ClInclude Include="..\..\library\check_crypto_config.h" />

     <ClInclude Include="..\..\library\common.h" />

+    <ClInclude Include="..\..\library\mps_common.h" />

+    <ClInclude Include="..\..\library\mps_error.h" />

+    <ClInclude Include="..\..\library\mps_reader.h" />

+    <ClInclude Include="..\..\library\mps_trace.h" />

     <ClInclude Include="..\..\library\psa_crypto_cipher.h" />

     <ClInclude Include="..\..\library\psa_crypto_core.h" />

     <ClInclude Include="..\..\library\psa_crypto_driver_wrappers.h" />

@@ -310,6 +314,8 @@
     <ClCompile Include="..\..\library\md4.c" />

     <ClCompile Include="..\..\library\md5.c" />

     <ClCompile Include="..\..\library\memory_buffer_alloc.c" />

+    <ClCompile Include="..\..\library\mps_reader.c" />

+    <ClCompile Include="..\..\library\mps_trace.c" />

     <ClCompile Include="..\..\library\net_sockets.c" />

     <ClCompile Include="..\..\library\nist_kw.c" />

     <ClCompile Include="..\..\library\oid.c" />