tls13-early-data.md: Fix reading early data documentation
Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/docs/tls13-early-data.md b/docs/tls13-early-data.md
index 28a8cc6..4b6f5d3 100644
--- a/docs/tls13-early-data.md
+++ b/docs/tls13-early-data.md
@@ -1,6 +1,6 @@
-Writing and reading early or 0-RTT data
----------------------------------------
+Writing early data
+------------------
An application function to write and send a buffer of data to a server through
TLS may plausibly look like:
@@ -144,34 +144,49 @@
data_written += early_data_written;
```
-Basically, the same holds for reading early data on the server side without the
-complication of possible rejection. An application function to read early data
-into a given buffer could plausibly look like:
+Reading early data
+------------------
+Mbed TLS provides the mbedtls_ssl_read_early_data() API to read the early data
+that a TLS 1.3 server might receive during the TLS 1.3 handshake.
+
+While establishing a TLS 1.3 connection with a client using a combination
+of the mbedtls_ssl_handshake(), mbedtls_ssl_read() and mbedtls_ssl_write() APIs,
+the reception of early data is signaled by an API returning the
+MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA error code. Early data can then be read
+with the mbedtls_ssl_read_early_data() API.
+
+For example, a typical code to establish a TLS connection, where ssl is the SSL
+context to use:
```
-int read_early_data( mbedtls_ssl_context *ssl,
- unsigned char *buffer,
- size_t buffer_size,
- size_t *data_len )
-{
- *data_len = 0;
+while ((int ret = mbedtls_ssl_handshake(&ssl)) != 0) {
- while( *data_len < buffer_size )
- {
- ret = mbedtls_ssl_read_early_data( ssl, buffer + *data_len,
- buffer_size - *data_len );
-
- if( ret < 0 &&
- ret != MBEDTLS_ERR_SSL_WANT_READ &&
- ret != MBEDTLS_ERR_SSL_WANT_WRITE )
- {
- return( ret );
- }
-
- *data_len += ret;
+ if (ret < 0 &&
+ ret != MBEDTLS_ERR_SSL_WANT_READ &&
+ ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
+ break;
}
-
- return( 0 );
}
```
-with again calls to read_early_data() expected to be done with a fresh SSL
-context.
+could be adapted to handle early data in the following way:
+```
+size_t data_read_len = 0;
+while ((ret = mbedtls_ssl_handshake(&ssl)) != 0) {
+
+ if (ret == MBEDTLS_ERR_SSL_RECEIVED_EARLY_DATA) {
+ ret = mbedtls_ssl_read_early_data(&ssl,
+ buffer + data_read_len,
+ sizeof(buffer) - data_read_len);
+ if (ret < 0) {
+ break;
+ }
+ data_read_len += ret;
+ continue;
+ }
+
+ if (ret < 0 &&
+ ret != MBEDTLS_ERR_SSL_WANT_READ &&
+ ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
+ break;
+ }
+}
+```