underlying BIO.
For the transparent negotiation to succeed, the B<ssl> must have been
-initialized to client or server mode. This is not the case if a generic
-method is being used (see L<SSL_CTX_new(3)|SSL_CTX_new(3)>, so that
+initialized to client or server mode. This is being done by calling
L<SSL_set_connect_state(3)|SSL_set_connect_state(3)> or SSL_set_accept_state()
-must be used before the first call to an SSL_read() or
-L<SSL_write(3)|SSL_write(3)> function.
+before the first call to an SSL_read() or L<SSL_write(3)|SSL_write(3)>
+function.
SSL_read() works based on the SSL/TLS records. The data are received in
records (with a maximum record size of 16kB for SSLv3/TLSv1). Only when a
If no more bytes are in the buffer, SSL_read() will trigger the processing
of the next record. Only when the record has been received and processed
completely, SSL_read() will return reporting success. At most the contents
-of the record will be returned.
+of the record will be returned. As the size of an SSL/TLS record may exceed
+the maximum packet size of the underlying transport (e.g. TCP), it may
+be necessary to read several packets from the transport layer before the
+record is complete and SSL_read() can succeed.
If the underlying BIO is B<blocking>, SSL_read() will only return, once the
read operation has been finished or an error occurred, except when a
for the required condition. When using a buffering BIO, like a BIO pair, data
must be written into or retrieved out of the BIO before being able to continue.
+L<SSL_pending(3)|SSL_pending(3)> can be used to find out whether there
+are buffered bytes available for immediate retrieval. In this case
+SSL_read() can be called without blocking or actually receiving new
+data from the underlying socket.
+
=head1 WARNING
When an SSL_read() operation has to be repeated because of
The read operation was successful; the return value is the number of
bytes actually read from the TLS/SSL connection.
-=item 0
+=item Z<>0
+
+The read operation was not successful. The reason may either be a clean
+shutdown due to a "close notify" alert sent by the peer (in which case
+the SSL_RECEIVED_SHUTDOWN flag in the ssl shutdown state is set
+(see L<SSL_shutdown(3)|SSL_shutdown(3)>,
+L<SSL_set_shutdown(3)|SSL_set_shutdown(3)>). It is also possible, that
+the peer simply shut down the underlying transport and the shutdown is
+incomplete. Call SSL_get_error() with the return value B<ret> to find out,
+whether an error occurred or the connection was shut down cleanly
+(SSL_ERROR_ZERO_RETURN).
-The read operation was not successful, probably because no data was
-available. Call SSL_get_error() with the return value B<ret> to find out,
-whether an error occurred.
+SSLv2 (deprecated) does not support a shutdown alert protocol, so it can
+only be detected, whether the underlying connection was closed. It cannot
+be checked, whether the closure was initiated by the peer or by something
+else.
=item E<lt>0
L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)|SSL_CTX_new(3)>,
L<SSL_connect(3)|SSL_connect(3)>, L<SSL_accept(3)|SSL_accept(3)>
L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>,
+L<SSL_pending(3)|SSL_pending(3)>,
+L<SSL_shutdown(3)|SSL_shutdown(3)>, L<SSL_set_shutdown(3)|SSL_set_shutdown(3)>,
L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>
=cut
projects / openssl.git / blobdiff