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SSL_write(3)                        OpenSSL                       SSL_write(3)



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

LIBRARY
       libcrypto, -lcrypto

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 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
       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 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 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.

WARNING
       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.

HISTORY
       SSL_write_ex() was added in OpenSSL 1.1.1.

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)

COPYRIGHT
       Copyright 2000-2018 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>.



1.1.1                             2018-09-17                      SSL_write(3)