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

NOTES
  If necessary, the SSL_write() function will negotiate a TLS/SSL session, if
  not already explicitly performed by SSL_connect() or SSL_accept(). If the
  peer requests a renegotiation, it will be performed transparently during
  the SSL_write() operation. The behavior 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 done by calling the
  SSL_set_connect_state() or SSL_set_accept_state() functions before the
  first call to an SSL_read() or SSL_write() function.

  If the underlying BIO is blocking, SSL_write() will only return once the
  write operation finishes or an error occurs, except when a renegotiation
  take place, in which case an SSL_ERROR_WANT_READ might occur.	 This
  behavior can be controlled with the SSL_MODE_AUTO_RETRY flag of the
  SSL_CTX_set_mode() function.

  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() with the return value
  of SSL_write() will yield SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE.  As
  at any time a renegotiation 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.

  The SSL_write() function will only return with success when the complete
  contents of buf of length num has been written. This default behavior can
  be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of
  SSL_CTX_set_mode().  When this flag is set, SSL_write() will also return
  with success when a partial write successfully completes. In this case, the
  SSL_write() operation is considered complete. The bytes are sent and a new
  SSL_write() operation with a new buffer (with the previously sent bytes
  removed) must be started. A partial write is performed with the size of a
  message block, which is 16kB for SSLv3/TLSv1.

RESTRICTIONS
  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.

WARNINGS
  When calling SSL_write() with num= 0 bytes  the behavior 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. The underlying connection
	  was probably closed. Call SSL_get_error() with the return value ret
	  to determine if 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 if an
	  underlying connection was closed. It cannot check 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 the reason.

SEE ALSO
  Functions: 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)

Index for Section 3

Alphabetical listing for S

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