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 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 nonblocking
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)
0.9.7l 2002-07-19 SSL_write(3)
|