.\"	$NetBSD: SSL_write.3,v 1.8 2003/07/24 14:16:47 itojun Exp $
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.\" ======================================================================
.\"
.IX Title "SSL_write 3"
.TH SSL_write 3 "0.9.7b" "2002-07-19" "OpenSSL"
.UC
.SH "NAME"
SSL_write \- write bytes to a \s-1TLS/SSL\s0 connection.
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/ssl.h>
.Ve
.Vb 1
\& int SSL_write(SSL *ssl, const void *buf, int num);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fISSL_write()\fR writes \fBnum\fR bytes from the buffer \fBbuf\fR into the specified
\&\fBssl\fR connection.
.SH "NOTES"
.IX Header "NOTES"
If necessary, \fISSL_write()\fR will negotiate a \s-1TLS/SSL\s0 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 \fISSL_write()\fR operation. The behaviour of \fISSL_write()\fR depends on the
underlying \s-1BIO\s0. 
.PP
For the transparent negotiation to succeed, the \fBssl\fR must have been
initialized to client or server mode. This is being done by calling
SSL_set_connect_state(3) or \fISSL_set_accept_state()\fR
before the first call to an SSL_read(3) or \fISSL_write()\fR function.
.PP
If the underlying \s-1BIO\s0 is \fBblocking\fR, \fISSL_write()\fR will only return, once the
write operation has been finished or an error occurred, except when a
renegotiation take place, in which case a \s-1SSL_ERROR_WANT_READ\s0 may occur. 
This behaviour can be controlled with the \s-1SSL_MODE_AUTO_RETRY\s0 flag of the
SSL_CTX_set_mode(3) call.
.PP
If the underlying \s-1BIO\s0 is \fBnon-blocking\fR, \fISSL_write()\fR will also return,
when the underlying \s-1BIO\s0 could not satisfy the needs of \fISSL_write()\fR
to continue the operation. In this case a call to
SSL_get_error(3) with the
return value of \fISSL_write()\fR will yield \fB\s-1SSL_ERROR_WANT_READ\s0\fR or
\&\fB\s-1SSL_ERROR_WANT_WRITE\s0\fR. As at any time a re-negotiation is possible, a
call to \fISSL_write()\fR can also cause read operations! The calling process
then must repeat the call after taking appropriate action to satisfy the
needs of \fISSL_write()\fR. The action depends on the underlying \s-1BIO\s0. When using a
non-blocking socket, nothing is to be done, but \fIselect()\fR can be used to check
for the required condition. When using a buffering \s-1BIO\s0, like a \s-1BIO\s0 pair, data
must be written into or retrieved out of the \s-1BIO\s0 before being able to continue.
.PP
\&\fISSL_write()\fR will only return with success, when the complete contents
of \fBbuf\fR of length \fBnum\fR has been written. This default behaviour
can be changed with the \s-1SSL_MODE_ENABLE_PARTIAL_WRITE\s0 option of
SSL_CTX_set_mode(3). When this flag is set,
\&\fISSL_write()\fR will also return with success, when a partial write has been
successfully completed. In this case the \fISSL_write()\fR operation is considered
completed. The bytes are sent and a new \fISSL_write()\fR 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.
.SH "WARNING"
.IX Header "WARNING"
When an \fISSL_write()\fR operation has to be repeated because of
\&\fB\s-1SSL_ERROR_WANT_READ\s0\fR or \fB\s-1SSL_ERROR_WANT_WRITE\s0\fR, it must be repeated
with the same arguments.
.PP
When calling \fISSL_write()\fR with num=0 bytes to be sent the behaviour is
undefined.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
The following return values can occur:
.Ip ">0" 4
.IX Item ">0"
The write operation was successful, the return value is the number of
bytes actually written to the \s-1TLS/SSL\s0 connection.
.Ip "0" 4
The write operation was not successful. Probably the underlying connection
was closed. Call \fISSL_get_error()\fR with the return value \fBret\fR to find out,
whether an error occurred or the connection was shut down cleanly
(\s-1SSL_ERROR_ZERO_RETURN\s0).
.Sp
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.
.Ip "<0" 4
.IX Item "<0"
The write operation was not successful, because either an error occurred
or action must be taken by the calling process. Call \fISSL_get_error()\fR with the
return value \fBret\fR to find out the reason.
.SH "SEE ALSO"
.IX Header "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), openssl_bio(3)