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132 .\" ========================================================================
134 .IX Title "SSL_write 3"
135 .TH SSL_write 3 "2009-04-11" "0.9.8k" "OpenSSL"
136 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
137 .\" way too many mistakes in technical documents.
141 SSL_write \- write bytes to a TLS/SSL connection.
143 .IX Header "SYNOPSIS"
145 \& #include <openssl/ssl.h>
147 \& int SSL_write(SSL *ssl, const void *buf, int num);
150 .IX Header "DESCRIPTION"
151 \&\fISSL_write()\fR writes \fBnum\fR bytes from the buffer \fBbuf\fR into the specified
152 \&\fBssl\fR connection.
155 If necessary, \fISSL_write()\fR will negotiate a \s-1TLS/SSL\s0 session, if
156 not already explicitly performed by \fISSL_connect\fR\|(3) or
157 \&\fISSL_accept\fR\|(3). If the
158 peer requests a re-negotiation, it will be performed transparently during
159 the \fISSL_write()\fR operation. The behaviour of \fISSL_write()\fR depends on the
160 underlying \s-1BIO\s0.
162 For the transparent negotiation to succeed, the \fBssl\fR must have been
163 initialized to client or server mode. This is being done by calling
164 \&\fISSL_set_connect_state\fR\|(3) or \fISSL_set_accept_state()\fR
165 before the first call to an \fISSL_read\fR\|(3) or \fISSL_write()\fR function.
167 If the underlying \s-1BIO\s0 is \fBblocking\fR, \fISSL_write()\fR will only return, once the
168 write operation has been finished or an error occurred, except when a
169 renegotiation take place, in which case a \s-1SSL_ERROR_WANT_READ\s0 may occur.
170 This behaviour can be controlled with the \s-1SSL_MODE_AUTO_RETRY\s0 flag of the
171 \&\fISSL_CTX_set_mode\fR\|(3) call.
173 If the underlying \s-1BIO\s0 is \fBnon-blocking\fR, \fISSL_write()\fR will also return,
174 when the underlying \s-1BIO\s0 could not satisfy the needs of \fISSL_write()\fR
175 to continue the operation. In this case a call to
176 \&\fISSL_get_error\fR\|(3) with the
177 return value of \fISSL_write()\fR will yield \fB\s-1SSL_ERROR_WANT_READ\s0\fR or
178 \&\fB\s-1SSL_ERROR_WANT_WRITE\s0\fR. As at any time a re-negotiation is possible, a
179 call to \fISSL_write()\fR can also cause read operations! The calling process
180 then must repeat the call after taking appropriate action to satisfy the
181 needs of \fISSL_write()\fR. The action depends on the underlying \s-1BIO\s0. When using a
182 non-blocking socket, nothing is to be done, but \fIselect()\fR can be used to check
183 for the required condition. When using a buffering \s-1BIO\s0, like a \s-1BIO\s0 pair, data
184 must be written into or retrieved out of the \s-1BIO\s0 before being able to continue.
186 \&\fISSL_write()\fR will only return with success, when the complete contents
187 of \fBbuf\fR of length \fBnum\fR has been written. This default behaviour
188 can be changed with the \s-1SSL_MODE_ENABLE_PARTIAL_WRITE\s0 option of
189 \&\fISSL_CTX_set_mode\fR\|(3). When this flag is set,
190 \&\fISSL_write()\fR will also return with success, when a partial write has been
191 successfully completed. In this case the \fISSL_write()\fR operation is considered
192 completed. The bytes are sent and a new \fISSL_write()\fR operation with a new
193 buffer (with the already sent bytes removed) must be started.
194 A partial write is performed with the size of a message block, which is
195 16kB for SSLv3/TLSv1.
198 When an \fISSL_write()\fR operation has to be repeated because of
199 \&\fB\s-1SSL_ERROR_WANT_READ\s0\fR or \fB\s-1SSL_ERROR_WANT_WRITE\s0\fR, it must be repeated
200 with the same arguments.
202 When calling \fISSL_write()\fR with num=0 bytes to be sent the behaviour is
205 .IX Header "RETURN VALUES"
206 The following return values can occur:
209 The write operation was successful, the return value is the number of
210 bytes actually written to the \s-1TLS/SSL\s0 connection.
212 The write operation was not successful. Probably the underlying connection
213 was closed. Call \fISSL_get_error()\fR with the return value \fBret\fR to find out,
214 whether an error occurred or the connection was shut down cleanly
215 (\s-1SSL_ERROR_ZERO_RETURN\s0).
217 SSLv2 (deprecated) does not support a shutdown alert protocol, so it can
218 only be detected, whether the underlying connection was closed. It cannot
219 be checked, why the closure happened.
222 The write operation was not successful, because either an error occurred
223 or action must be taken by the calling process. Call \fISSL_get_error()\fR with the
224 return value \fBret\fR to find out the reason.
226 .IX Header "SEE ALSO"
227 \&\fISSL_get_error\fR\|(3), \fISSL_read\fR\|(3),
228 \&\fISSL_CTX_set_mode\fR\|(3), \fISSL_CTX_new\fR\|(3),
229 \&\fISSL_connect\fR\|(3), \fISSL_accept\fR\|(3)
230 \&\fISSL_set_connect_state\fR\|(3),
231 \&\fIssl\fR\|(3), \fIbio\fR\|(3)