=pod

=head1 NAME

SSL_write_ex, SSL_write - write bytes to a TLS/SSL connection

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 int SSL_write_ex(SSL *s, const void *buf, size_t num, size_t *written);

 int SSL_write(SSL *ssl, const void *buf, int num);

=head1 DESCRIPTION

SSL_write_ex() and SSL_write() write B<num> bytes from the buffer B<buf> into

the specified B<ssl> connection. On success SSL_write_ex() will store the number

of bytes written in B<*written>.

=head1 NOTES

In the paragraphs below a "write function" is defined as one of either

SSL_write_ex(), or SSL_write().

If necessary, a write function will negotiate a TLS/SSL session, if not already

explicitly performed by L<SSL_connect(3)> or L<SSL_accept(3)>. If the peer

requests a re-negotiation, it will be performed transparently during

the write function operation. The behaviour of the write functions 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)> or SSL_set_accept_state()

before the first call to a write function.

If the underlying BIO is B<blocking>, the write functions will only return, once

the write operation has been finished or an error occurred.

If the underlying BIO is B<non-blocking> the write functions will also return

when the underlying BIO could not satisfy the needs of the function to continue

the operation. In this case a call to L<SSL_get_error(3)> with the

return value of the write function 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 a write function can also cause read operations! The calling process

then must repeat the call after taking appropriate action to satisfy the needs

of the write function. 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.

The write functions 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)>. When

this flag is set the write functions will also return with success when a

partial write has been successfully completed. In this case the write function

operation is considered completed. The bytes are sent and a new write call 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.

=head1 WARNINGS

When a write function call has to be repeated because L<SSL_get_error(3)>

returned B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated

with the same arguments.

The data that was passed might have been partially processed.

When B<SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER> was set using L<SSL_CTX_set_mode(3)>

the pointer can be different, but the data and length should still be the same.

You should not call SSL_write() with num=0, it will return an error.

SSL_write_ex() can be called with num=0, but will not send application data to

the peer.

=head1 RETURN VALUES

SSL_write_ex() will return 1 for success or 0 for failure. Success means that

all requested application data bytes have been written to the SSL connection or,

if SSL_MODE_ENABLE_PARTIAL_WRITE is in use, at least 1 application data byte has

been written to the SSL connection. Failure means that not all the requested

bytes have been written yet (if SSL_MODE_ENABLE_PARTIAL_WRITE is not in use) or

no bytes could be written to the SSL connection (if

SSL_MODE_ENABLE_PARTIAL_WRITE is in use). Failures can be retryable (e.g. the

network write buffer has temporarily filled up) or non-retryable (e.g. a fatal

network error). In the event of a failure call L<SSL_get_error(3)> to find out

the reason which indicates whether the call is retryable or not.

For SSL_write() 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, because either the connection was

closed, 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.

Old documentation indicated a difference between 0 and -1, and that -1 was

retryable.

You should instead call SSL_get_error() to find out if it's retryable.

=back

=head1 SEE ALSO

L<SSL_get_error(3)>, L<SSL_read_ex(3)>, L<SSL_read(3)>

L<SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)>,

L<SSL_connect(3)>, L<SSL_accept(3)>

L<SSL_set_connect_state(3)>,

L<ssl(7)>, L<bio(7)>

=head1 HISTORY

The SSL_write_ex() function was added in OpenSSL 1.1.1.

=head1 COPYRIGHT

Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use

this file except in compliance with the License.  You can obtain a copy

in the file LICENSE in the source distribution or at

L<https://www.openssl.org/source/license.html>.

=cut