SSL_write_ex

SSL_WRITE(3)                         OpenSSL                        SSL_WRITE(3)



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

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);

DESCRIPTION
       SSL_write_ex() and SSL_write() write num bytes from the buffer buf into
       the specified ssl connection. On success SSL_write_ex() will store the
       number of bytes written in *written.

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 SSL_connect(3) or 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 ssl must have been
       initialized to client or server mode. This is being done by calling
       SSL_set_connect_state(3) or SSL_set_accept_state() before the first call
       to a write function.

       If the underlying BIO is blocking, the write functions will only return,
       once the write operation has been finished or an error occurred.

       If the underlying BIO is nonblocking 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 SSL_get_error(3) with the
       return value of the write function will yield SSL_ERROR_WANT_READ or
       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 nonblocking 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 buf of length num has been written. This default behaviour
       can be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of
       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.

WARNINGS
       When a write function call has to be repeated because SSL_get_error(3)
       returned SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE, it must be repeated
       with the same arguments.  The data that was passed might have been
       partially processed.  When SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER was set
       using 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.

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 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:

       > 0 The write operation was successful, the return value is the number of
           bytes actually written to the TLS/SSL connection.

       <= 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 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.

SEE ALSO
       SSL_get_error(3), SSL_read_ex(3), SSL_read(3) SSL_CTX_set_mode(3),
       SSL_CTX_new(3), SSL_connect(3), SSL_accept(3) SSL_set_connect_state(3),
       ssl(7), bio(7)

HISTORY
       The SSL_write_ex() function was added in OpenSSL 1.1.1.

COPYRIGHT
       Copyright 2000-2020 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
       <https://www.openssl.org/source/license.html>.



1.1.1l                             2021-08-24                       SSL_WRITE(3)