SSL_write(3)

     SSL_write(3)           0.9.6h (2002-07-19)           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 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

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     SSL_write(3)           0.9.6h (2002-07-19)           SSL_write(3)

          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)

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