Initial Commit

openssl-1.0.2f/doc/ssl/SSL_write.pod

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+=pod
+
+=head1 NAME
+
+SSL_write - write bytes to a TLS/SSL connection.
+
+=head1 SYNOPSIS
+
+ #include <openssl/ssl.h>
+
+ int SSL_write(SSL *ssl, const void *buf, int num);
+
+=head1 DESCRIPTION
+
+SSL_write() writes B<num> bytes from the buffer B<buf> into the specified
+B<ssl> connection.
+
+=head1 NOTES
+
+If necessary, SSL_write() 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_write() operation. The behaviour of SSL_write() 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 L<SSL_read(3)|SSL_read(3)> or SSL_write() function.
+
+If the underlying BIO is B<blocking>, SSL_write() will only return, once the
+write 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_write() will also return,
+when the underlying BIO could not satisfy the needs of SSL_write()
+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_write() 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_write() can also cause read operations! The calling process
+then must repeat the call after taking appropriate action to satisfy the
+needs of SSL_write(). 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.
+
+SSL_write() will only return with success, when the complete contents
+of B<buf> of length B<num> has been written. This default behaviour
+can be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of
+L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>. When this flag is set,
+SSL_write() will also return with success, when a partial write has been
+successfully completed. In this case the SSL_write() operation is considered
+completed. The bytes are sent and a new SSL_write() operation with a new
+buffer (with the already sent bytes removed) must be started.
+A partial write is performed with the size of a message block, which is
+16kB for SSLv3/TLSv1.
+
+=head1 WARNING
+
+When an SSL_write() 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.
+
+When calling SSL_write() with num=0 bytes to be sent the behaviour is
+undefined.
+
+=head1 RETURN VALUES
+
+The following return values can occur:
+
+=over 4
+
+=item E<gt>0
+
+The write operation was successful, the return value is the number of
+bytes actually written to the TLS/SSL connection.
+
+=item Z<>0
+
+The write operation was not successful. Probably the underlying connection
+was closed. 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, why the closure happened.
+
+=item E<lt>0
+
+The write 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_read(3)|SSL_read(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(3)|ssl(3)>, L<bio(3)|bio(3)>
+
+=cut