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[dragonfly.git] / secure / lib / libssl / man / SSL_write.3
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138.\" ======================================================================
139.\"
140.IX Title "SSL_write 3"
141.TH SSL_write 3 "0.9.7a" "2003-02-19" "OpenSSL"
142.UC
143.SH "NAME"
144SSL_write \- write bytes to a \s-1TLS/SSL\s0 connection.
145.SH "SYNOPSIS"
146.IX Header "SYNOPSIS"
147.Vb 1
148\& #include <openssl/ssl.h>
149.Ve
150.Vb 1
151\& int SSL_write(SSL *ssl, const void *buf, int num);
152.Ve
153.SH "DESCRIPTION"
154.IX Header "DESCRIPTION"
155\&\fISSL_write()\fR writes \fBnum\fR bytes from the buffer \fBbuf\fR into the specified
156\&\fBssl\fR connection.
157.SH "NOTES"
158.IX Header "NOTES"
159If necessary, \fISSL_write()\fR will negotiate a \s-1TLS/SSL\s0 session, if
160not already explicitly performed by SSL_connect(3) or
161SSL_accept(3). If the
162peer requests a re-negotiation, it will be performed transparently during
163the \fISSL_write()\fR operation. The behaviour of \fISSL_write()\fR depends on the
164underlying \s-1BIO\s0.
165.PP
166For the transparent negotiation to succeed, the \fBssl\fR must have been
167initialized to client or server mode. This is being done by calling
168SSL_set_connect_state(3) or \fISSL_set_accept_state()\fR
169before the first call to an SSL_read(3) or \fISSL_write()\fR function.
170.PP
171If the underlying \s-1BIO\s0 is \fBblocking\fR, \fISSL_write()\fR will only return, once the
172write operation has been finished or an error occurred, except when a
173renegotiation take place, in which case a \s-1SSL_ERROR_WANT_READ\s0 may occur.
174This behaviour can be controlled with the \s-1SSL_MODE_AUTO_RETRY\s0 flag of the
175SSL_CTX_set_mode(3) call.
176.PP
177If the underlying \s-1BIO\s0 is \fBnon-blocking\fR, \fISSL_write()\fR will also return,
178when the underlying \s-1BIO\s0 could not satisfy the needs of \fISSL_write()\fR
179to continue the operation. In this case a call to
180SSL_get_error(3) with the
181return value of \fISSL_write()\fR will yield \fB\s-1SSL_ERROR_WANT_READ\s0\fR or
182\&\fB\s-1SSL_ERROR_WANT_WRITE\s0\fR. As at any time a re-negotiation is possible, a
183call to \fISSL_write()\fR can also cause read operations! The calling process
184then must repeat the call after taking appropriate action to satisfy the
185needs of \fISSL_write()\fR. The action depends on the underlying \s-1BIO\s0. When using a
186non-blocking socket, nothing is to be done, but \fIselect()\fR can be used to check
187for the required condition. When using a buffering \s-1BIO\s0, like a \s-1BIO\s0 pair, data
188must be written into or retrieved out of the \s-1BIO\s0 before being able to continue.
189.PP
190\&\fISSL_write()\fR will only return with success, when the complete contents
191of \fBbuf\fR of length \fBnum\fR has been written. This default behaviour
192can be changed with the \s-1SSL_MODE_ENABLE_PARTIAL_WRITE\s0 option of
193SSL_CTX_set_mode(3). When this flag is set,
194\&\fISSL_write()\fR will also return with success, when a partial write has been
195successfully completed. In this case the \fISSL_write()\fR operation is considered
196completed. The bytes are sent and a new \fISSL_write()\fR operation with a new
197buffer (with the already sent bytes removed) must be started.
198A partial write is performed with the size of a message block, which is
19916kB for SSLv3/TLSv1.
200.SH "WARNING"
201.IX Header "WARNING"
202When an \fISSL_write()\fR operation has to be repeated because of
203\&\fB\s-1SSL_ERROR_WANT_READ\s0\fR or \fB\s-1SSL_ERROR_WANT_WRITE\s0\fR, it must be repeated
204with the same arguments.
205.PP
206When calling \fISSL_write()\fR with num=0 bytes to be sent the behaviour is
207undefined.
208.SH "RETURN VALUES"
209.IX Header "RETURN VALUES"
210The following return values can occur:
211.Ip ">0" 4
212.IX Item ">0"
213The write operation was successful, the return value is the number of
214bytes actually written to the \s-1TLS/SSL\s0 connection.
215.Ip "0" 4
216The write operation was not successful. Probably the underlying connection
217was closed. Call \fISSL_get_error()\fR with the return value \fBret\fR to find out,
218whether an error occurred or the connection was shut down cleanly
219(\s-1SSL_ERROR_ZERO_RETURN\s0).
220.Sp
221SSLv2 (deprecated) does not support a shutdown alert protocol, so it can
222only be detected, whether the underlying connection was closed. It cannot
223be checked, why the closure happened.
224.Ip "<0" 4
225.IX Item "<0"
226The write operation was not successful, because either an error occurred
227or action must be taken by the calling process. Call \fISSL_get_error()\fR with the
228return value \fBret\fR to find out the reason.
229.SH "SEE ALSO"
230.IX Header "SEE ALSO"
231SSL_get_error(3), SSL_read(3),
232SSL_CTX_set_mode(3), SSL_CTX_new(3),
233SSL_connect(3), SSL_accept(3)
234SSL_set_connect_state(3),
235ssl(3), bio(3)