SSL_WRITE(3) OpenSSL SSL_WRITE(3)
SSL_write - write bytes to a TLS/SSL connection.
#include <openssl/ssl.h>
int SSL_write(SSL *ssl, const void *buf, int num);
SSL_write() writes num bytes from the buffer buf into the
specified ssl connection.
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 opera-
tions! 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
MirOS BSD #10-current 2005-02-05 1
SSL_WRITE(3) OpenSSL 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 com-
pleted. In this case the SSL_write() operation is considered
completed. The bytes are sent and a new SSL_write() opera-
tion 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.
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.
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 con-
nection.
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 under-
lying 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.
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)
MirOS BSD #10-current 2005-02-05 2
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