Implement stages except write_partial

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index 46c071b..b06147c 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -99,7 +99,6 @@
 
     MBEDTLS_SSL_PROC_CHK( ssl_client_hello_postprocess, ( ssl ) );
     MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_finish_handshake_msg, ( ssl, buf_len, msg_len ) );
-    mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_SERVER_HELLO );
 
 cleanup:
 
@@ -111,8 +110,31 @@
 
 static int ssl_client_hello_prepare( mbedtls_ssl_context* ssl )
 {
-    ((void) ssl);
-    return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
+    int ret;
+    size_t rand_bytes_len;
+
+    if( ssl->conf->f_rng == NULL )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "no RNG provided" ) );
+        return( MBEDTLS_ERR_SSL_NO_RNG );
+    }
+
+    rand_bytes_len = 32;
+
+    if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng, ssl->handshake->randbytes, rand_bytes_len ) ) != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1, "ssl_generate_random", ret );
+        return( ret );
+    }
+
+    return( 0 );
+}
+
+static int ssl_client_hello_postprocess( mbedtls_ssl_context* ssl )
+{
+    mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_SERVER_HELLO );
+
+    return( 0 );
 }
 
 static int ssl_client_hello_write_partial( mbedtls_ssl_context* ssl,
@@ -128,11 +150,7 @@
     return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
 }
 
-static int ssl_client_hello_postprocess( mbedtls_ssl_context* ssl )
-{
-    ((void) ssl);
-    return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
-}
+
 
 #endif /* MBEDTLS_SSL_CLI_C */