Add session saving/loading

For now, the header (version+format bytes) is duplicated. This might be
optimized later.

include/mbedtls/ssl.h

@@ -3926,7 +3926,11 @@ void mbedtls_ssl_free( mbedtls_ssl_context *ssl );
  * \note           \p olen is updated to the correct value regardless of
  *                 whether \p buf_len was large enough. This makes it possible
  *                 to determine the necessary size by calling this function
- *                 with \p buf set to \c NULL and \p buf_len to \c 0.
+ *                 with \p buf set to \c NULL and \p buf_len to \c 0. However,
+ *                 the value of \p olen is only guaranteed to be correct when
+ *                 the function returns #MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL or
+ *                 \c 0. If the return value is different, then the value of
+ *                 \p olen is undefined.
  *
  * \return         \c 0 if successful.
  * \return         #MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL if \p buf is too small.
@@ -3991,6 +3995,11 @@ int mbedtls_ssl_context_save( mbedtls_ssl_context *ssl,
  *                 newly-configured value with the value that was active when
  *                 the context was saved.
  *
+ * \note           When this function returns an error code, it calls
+ *                 mbedtls_ssl_free() on \p ssl. In this case, you need to
+ *                 prepare the context with the usual sequence starting with a
+ *                 call to mbedtls_ssl_init() if you want to use it again.
+ *
  * \param ssl      The SSL context structure to be populated. It must have
  *                 been prepared as described in the note above.
  * \param buf      The buffer holding the serialized connection data. It must

library/ssl_tls.c

@@ -10775,6 +10775,8 @@ int mbedtls_ssl_context_save( mbedtls_ssl_context *ssl,
 {
     unsigned char *p = buf;
     size_t used = 0;
+    size_t session_len;
+    int ret = 0;
 
     /*
      * Enforce current usage restrictions
@@ -10815,6 +10817,29 @@ int mbedtls_ssl_context_save( mbedtls_ssl_context *ssl,
         p += sizeof( ssl_serialized_context_header );
     }
 
+    /*
+     * Session (length + data)
+     */
+    ret = mbedtls_ssl_session_save( ssl->session, NULL, 0, &session_len );
+    if( ret != MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL )
+        return( ret );
+
+    used += 4 + session_len;
+    if( used <= buf_len )
+    {
+        *p++ = (unsigned char)( ( session_len >> 24 ) & 0xFF );
+        *p++ = (unsigned char)( ( session_len >> 16 ) & 0xFF );
+        *p++ = (unsigned char)( ( session_len >>  8 ) & 0xFF );
+        *p++ = (unsigned char)( ( session_len       ) & 0xFF );
+
+        ret = mbedtls_ssl_session_save( ssl->session,
+                                        p, session_len, &session_len );
+        if( ret != 0 )
+            return( ret );
+
+        p += session_len;
+    }
+
     /*
      * Done
      */
@@ -10823,18 +10848,25 @@ int mbedtls_ssl_context_save( mbedtls_ssl_context *ssl,
     if( used > buf_len )
         return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
 
+    MBEDTLS_SSL_DEBUG_BUF( 4, "saved context", buf, used );
+
     return( 0 );
 }
 
 /*
- * Deserialize a full SSL context
+ * Unserialize context, see mbedtls_ssl_context_save() for format.
+ *
+ * This internal version is wrapped by a public function that cleans up in
+ * case of error.
  */
-int mbedtls_ssl_context_load( mbedtls_ssl_context *ssl,
-                              const unsigned char *buf,
-                              size_t len )
+static int ssl_context_load( mbedtls_ssl_context *ssl,
+                             const unsigned char *buf,
+                             size_t len )
 {
     const unsigned char *p = buf;
     const unsigned char * const end = buf + len;
+    size_t session_len;
+    int ret;
 
     /*
      * The context should have been freshly setup or reset.
@@ -10865,6 +10897,8 @@ int mbedtls_ssl_context_load( mbedtls_ssl_context *ssl,
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
     }
 
+    MBEDTLS_SSL_DEBUG_BUF( 4, "context to load", buf, len );
+
     /*
      * Check version identifier
      */
@@ -10878,6 +10912,35 @@ int mbedtls_ssl_context_load( mbedtls_ssl_context *ssl,
     }
     p += sizeof( ssl_serialized_context_header );
 
+    /*
+     * Session
+     */
+    if( (size_t)( end - p ) < 4 )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
+    session_len = ( (size_t) p[0] << 24 ) |
+                  ( (size_t) p[1] << 16 ) |
+                  ( (size_t) p[2] <<  8 ) |
+                  ( (size_t) p[3]       );
+    p += 4;
+
+    ssl->session = mbedtls_calloc( 1, sizeof( mbedtls_ssl_session ) );
+    if( ssl->session == NULL )
+        return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
+    mbedtls_ssl_session_init( ssl->session );
+
+    ssl->session_in = ssl->session;
+    ssl->session_out = ssl->session;
+
+    if( (size_t)( end - p ) < session_len )
+        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
+
+    ret = mbedtls_ssl_session_load( ssl->session, p, session_len );
+    if( ret != 0 )
+        return( ret );
+
+    p += session_len;
+
     /*
      * Done - should have consumed entire buffer
      */
@@ -10887,6 +10950,21 @@ int mbedtls_ssl_context_load( mbedtls_ssl_context *ssl,
     return( 0 );
 }
 
+/*
+ * Unserialize context: public wrapper for error cleaning
+ */
+int mbedtls_ssl_context_load( mbedtls_ssl_context *context,
+                              const unsigned char *buf,
+                              size_t len )
+{
+    int ret = ssl_context_load( context, buf, len );
+
+    if( ret != 0 )
+        mbedtls_ssl_free( context );
+
+    return( ret );
+}
+
 /*
  * Free an SSL context
  */