--- /dev/null
+=pod
+
+=head1 NAME
+
+SSL_read - read bytes from a TLS/SSL connection.
+
+=head1 SYNOPSIS
+
+ #include <openssl/ssl.h>
+
+ int SSL_read(SSL *ssl, void *buf, int num);
+
+=head1 DESCRIPTION
+
+SSL_read() tries to read B<num> bytes from the specified B<ssl> into the
+buffer B<buf>.
+
+=head1 NOTES
+
+If necessary, SSL_read() will negotiate a TLS/SSL session, if
+not already explicitly performed by L<SSL_connect(3)|SSL_connect(3)> or
+L<SSL_accept(3)|SSL_accept(3)>. If the
+peer requests a re-negotiation, it will be performed transparently during
+the SSL_read() operation. The behaviour of SSL_read() depends on the
+underlying BIO.
+
+For the transparent negotiation to succeed, the B<ssl> must have been
+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()
+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
+record has been completely received, it can be processed (decryption and
+check of integrity). Therefore data that was not retrieved at the last
+call of SSL_read() can still be buffered inside the SSL layer and will be
+retrieved on the next call to SSL_read(). If B<num> is higher than the
+number of bytes buffered, SSL_read() will return with the bytes buffered.
+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. 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
+renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur.
+This behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the
+L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> call.
+
+If the underlying BIO is B<non-blocking>, SSL_read() will also return
+when the underlying BIO could not satisfy the needs of SSL_read()
+to continue the operation. In this case a call to
+L<SSL_get_error(3)|SSL_get_error(3)> with the
+return value of SSL_read() will yield B<SSL_ERROR_WANT_READ> or
+B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
+call to SSL_read() can also cause write operations! The calling process
+then must repeat the call after taking appropriate action to satisfy the
+needs of SSL_read(). The action depends on the underlying BIO. When using a
+non-blocking socket, nothing is to be done, but select() can be used to check
+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
+B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
+with the same arguments.
+
+=head1 RETURN VALUES
+
+The following return values can occur:
+
+=over 4
+
+=item E<gt>0
+
+The read operation was successful; the return value is the number of
+bytes actually read from the TLS/SSL connection.
+
+=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).
+
+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
+
+The read operation was not successful, because either an error occurred
+or action must be taken by the calling process. Call SSL_get_error() with the
+return value B<ret> to find out the reason.
+
+=back
+
+=head1 SEE ALSO
+
+L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_write(3)|SSL_write(3)>,
+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 / cassiopeia.git / blobdiff