Merge 'mbedtls/development' into merge-crypto-unremoved-20200304

Merge the latest state of the target branch (mbedtls/development) into the
pull request to merge mbed-crypto into mbedtls.

Conflicts:

* ChangeLog: add/add conflict. Resolve by using the usual section order.

include/mbedtls/ssl.h

@@ -1215,6 +1215,9 @@ struct mbedtls_ssl_context
     int in_msgtype;             /*!< record header: message type      */
     size_t in_msglen;           /*!< record header: message length    */
     size_t in_left;             /*!< amount of data read so far       */
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t in_buf_len;          /*!< length of input buffer           */
+#endif
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
     uint16_t in_epoch;          /*!< DTLS epoch for incoming records  */
     size_t next_record_offset;  /*!< offset of the next record in datagram
@@ -1254,6 +1257,9 @@ struct mbedtls_ssl_context
     int out_msgtype;            /*!< record header: message type      */
     size_t out_msglen;          /*!< record header: message length    */
     size_t out_left;            /*!< amount of data not yet written   */
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+    size_t out_buf_len;         /*!< length of output buffer          */
+#endif
 
     unsigned char cur_out_ctr[8]; /*!<  Outgoing record sequence  number. */
 
@@ -3733,7 +3739,14 @@ int mbedtls_ssl_renegotiate( mbedtls_ssl_context *ssl );
  *
  * \return         The (positive) number of bytes read if successful.
  * \return         \c 0 if the read end of the underlying transport was closed
- *                 - in this case you must stop using the context (see below).
+ *                 without sending a CloseNotify beforehand, which might happen
+ *                 because of various reasons (internal error of an underlying
+ *                 stack, non-conformant peer not sending a CloseNotify and
+ *                 such) - in this case you must stop using the context
+ *                 (see below).
+ * \return         #MBEDTLS_ERR_SSL_PEER_CLOSE_NOTIFY if the underlying
+ *                 transport is still functional, but the peer has
+ *                 acknowledged to not send anything anymore.
  * \return         #MBEDTLS_ERR_SSL_WANT_READ or #MBEDTLS_ERR_SSL_WANT_WRITE
  *                 if the handshake is incomplete and waiting for data to
  *                 be available for reading from or writing to the underlying