SSL_write(3SSL)                              OpenSSL                              SSL_write(3SSL)



NAME
       SSL_write - write bytes to a TLS/SSL connection.

SYNOPSIS
        #include <openssl/ssl.h>

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

DESCRIPTION
       SSL_write() writes num bytes from the buffer buf into the specified ssl connection.

NOTES
       If necessary, SSL_write() 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 SSL_write() operation. The behaviour of
       SSL_write() 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 an SSL_read(3) or SSL_write() function.

       If the underlying BIO is blocking, SSL_write() will only return, once the 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 SSL_CTX_set_mode(3) call.

       If the underlying BIO is 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(3) with the return value of SSL_write() will yield
       SSL_ERROR_WANT_READ or 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.

       SSL_write() 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,
       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.

WARNING
       When an SSL_write() operation has to be repeated because of SSL_ERROR_WANT_READ or
       SSL_ERROR_WANT_WRITE, it must be repeated with the same arguments.

       When calling SSL_write() with num=0 bytes to be sent the behaviour is undefined.

RETURN VALUES
       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. Probably the underlying connection was closed.
           Call SSL_get_error() with the return value 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.

       <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 ret
           to find out the reason.

SEE ALSO
       SSL_get_error(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(3), bio(3)



1.0.1t                                      2016-05-03                            SSL_write(3SSL)