xref: /freebsd-11.0-release/crypto/openssl/doc/ssl/SSL_write.pod

=pod

=head1 NAME

SSL_write - write bytes to a TLS/SSL connection.

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 int SSL_write(SSL *ssl, char *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 SSL_connect() or SSL_accept(). 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. 

If the underlying BIO is B<blocking>, SSL_write() will only return, once the
write operation has been finished or an error occurred.

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
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.

=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:

=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 0

The write operation was not successful. Call SSL_get_error() with the return
value B<ret> to find out, whether an error occurred.

=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(3)|ssl(3)>, L<bio(3)|bio(3)>

=cut