=head1 NAME
-SSL_read - write bytes to a TLS/SSL connection.
+SSL_write - write bytes to a TLS/SSL connection.
=head1 SYNOPSIS
#include <openssl/ssl.h>
- int SSL_write(SSL *ssl, char *buf, int num);
+ 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>. If necessary, SSL_write() will negotiate a TLS/SSL session, if
-not already explicitly performed by SSL_connect() or SSL_accept(). If the
+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 behavior of SSL_write() depends on the
+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.
+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 SSL_get_error() with the
+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 write operations! The calling process
+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.
+
=head1 RETURN VALUES
The following return values can occur:
=item 0
-The write operation was not successful. Call SSL_get_error() with the return
-value B<ret> to find out, whether an error occurred.
+The write operation was not successful, because the write side of the
+SSL connection was shut down (the SSL_SENT_SHUTDOWN flag in the shutdown
+state is set) by calling L<SSL_shutdown(3)|SSL_shutdown(3)> or
+L<SSL_set_shutdown(3)|SSL_set_shutdown(3)>. It is also possible, that 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 -1
+=item E<lt>0
-The read operation was not successful, because either an error occurred
+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.
=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
projects / openssl.git / blobdiff