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Enhance and extend checking of message processing state

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-  Enhances the documentation of mbedtls_ssl_get_bytes_avail (return
   the number of bytes left in the current application data record, if
   there is any).
-  Introduces a new public function mbedtls_ssl_check_pending for
   checking whether any data in the internal buffers still needs to be
   processed. This is necessary for users implementing event-driven IO
   to decide when they can safely idle until they receive further
   events from the underlying transport.
This commit is contained in:
Hanno Becker
2017-10-10 11:51:19 +01:00
parent 16970d2912
commit 8b170a0a0b
2 changed files with 106 additions and 2 deletions
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47
include/mbedtls/ssl.h
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@ -2235,11 +2235,54 @@ void mbedtls_ssl_conf_renegotiation_period( mbedtls_ssl_config *conf,
#endif /* MBEDTLS_SSL_RENEGOTIATION */
/**
* \brief Return the number of data bytes available to read
* \brief Check if there is data already read from the
* underlying transport but not yet processed.
*
* \param ssl SSL context
*
* \return how many bytes are available in the read buffer
* \return 0 if nothing's pending, 1 otherwise.
*
* \note This function is essential when using the library
* with event-driven I/O. The user should not idle
* (waiting for events from the underlying transport
* or from timers) before this function's check passes.
* Otherwise, it's possible to run into a deadlock
* (if processing the pending data involves essential
* communication with the peer) or to accumulate and
* potentially lose data.
*
* \note This is different in purpose and behaviour from
* \c mbedtls_ssl_get_bytes_avail in that it considers
* any kind of unprocessed data, not only unread
* application data. If \c mbedtls_ssl_get_bytes
* returns a non-zero value, this function will
* also signal pending data, but the converse does
* not hold. For example, in DTLS there might be
* further records waiting to be processed from
* the current underlying transport's datagram.
*
* \note If this function returns 0 (data pending), this
* does not imply that a subsequent call to
* \c mbedtls_ssl_read will provide any data;
* e.g., the unprocessed data might turn out
* to be an alert or a handshake message.
*/
int mbedtls_ssl_check_pending( const mbedtls_ssl_context *ssl );
/**
* \brief Return the number of application data bytes
* remaining to be read from the current record.
*
* \param ssl SSL context
*
* \return How many bytes are available in the application
* data record read buffer.
*
* \note When working over a datagram transport, this is
* useful to detect the current datagram's boundary
* in case \c mbedtls_ssl_read has written the maximal
* amount of data fitting into the input buffer.
*
*/
size_t mbedtls_ssl_get_bytes_avail( const mbedtls_ssl_context *ssl );