SSL_write(3)                OpenSSL                SSL_write(3)





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 ses-
       sion, if not already explicitly performed by SSL_con-
       nect(3) or SSL_accept(3). If the peer requests a
       re-negotiation, it will be performed transparently dur-
       ing 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 be-
       haviour 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 underly-
       ing 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 com-
       plete 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.

       o   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)



0.9.7c                     2002-07-19              SSL_write(3)
