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131 .IX Title "SSL_write 3"
132 .TH SSL_write 3 "2007-03-15" "0.9.8e" "OpenSSL"
134 SSL_write \- write bytes to a TLS/SSL connection.
136 .IX Header "SYNOPSIS"
138 \& #include <openssl/ssl.h>
142 \& int SSL_write(SSL *ssl, const void *buf, int num);
145 .IX Header "DESCRIPTION"
146 \&\fISSL_write()\fR writes \fBnum\fR bytes from the buffer \fBbuf\fR into the specified
147 \&\fBssl\fR connection.
150 If necessary, \fISSL_write()\fR will negotiate a \s-1TLS/SSL\s0 session, if
151 not already explicitly performed by \fISSL_connect\fR\|(3) or
152 \&\fISSL_accept\fR\|(3). If the
153 peer requests a re\-negotiation, it will be performed transparently during
154 the \fISSL_write()\fR operation. The behaviour of \fISSL_write()\fR depends on the
155 underlying \s-1BIO\s0.
157 For the transparent negotiation to succeed, the \fBssl\fR must have been
158 initialized to client or server mode. This is being done by calling
159 \&\fISSL_set_connect_state\fR\|(3) or \fISSL_set_accept_state()\fR
160 before the first call to an \fISSL_read\fR\|(3) or \fISSL_write()\fR function.
162 If the underlying \s-1BIO\s0 is \fBblocking\fR, \fISSL_write()\fR will only return, once the
163 write operation has been finished or an error occurred, except when a
164 renegotiation take place, in which case a \s-1SSL_ERROR_WANT_READ\s0 may occur.
165 This behaviour can be controlled with the \s-1SSL_MODE_AUTO_RETRY\s0 flag of the
166 \&\fISSL_CTX_set_mode\fR\|(3) call.
168 If the underlying \s-1BIO\s0 is \fBnon-blocking\fR, \fISSL_write()\fR will also return,
169 when the underlying \s-1BIO\s0 could not satisfy the needs of \fISSL_write()\fR
170 to continue the operation. In this case a call to
171 \&\fISSL_get_error\fR\|(3) with the
172 return value of \fISSL_write()\fR will yield \fB\s-1SSL_ERROR_WANT_READ\s0\fR or
173 \&\fB\s-1SSL_ERROR_WANT_WRITE\s0\fR. As at any time a re-negotiation is possible, a
174 call to \fISSL_write()\fR can also cause read operations! The calling process
175 then must repeat the call after taking appropriate action to satisfy the
176 needs of \fISSL_write()\fR. The action depends on the underlying \s-1BIO\s0. When using a
177 non-blocking socket, nothing is to be done, but \fIselect()\fR can be used to check
178 for the required condition. When using a buffering \s-1BIO\s0, like a \s-1BIO\s0 pair, data
179 must be written into or retrieved out of the \s-1BIO\s0 before being able to continue.
181 \&\fISSL_write()\fR will only return with success, when the complete contents
182 of \fBbuf\fR of length \fBnum\fR has been written. This default behaviour
183 can be changed with the \s-1SSL_MODE_ENABLE_PARTIAL_WRITE\s0 option of
184 \&\fISSL_CTX_set_mode\fR\|(3). When this flag is set,
185 \&\fISSL_write()\fR will also return with success, when a partial write has been
186 successfully completed. In this case the \fISSL_write()\fR operation is considered
187 completed. The bytes are sent and a new \fISSL_write()\fR operation with a new
188 buffer (with the already sent bytes removed) must be started.
189 A partial write is performed with the size of a message block, which is
190 16kB for SSLv3/TLSv1.
193 When an \fISSL_write()\fR operation has to be repeated because of
194 \&\fB\s-1SSL_ERROR_WANT_READ\s0\fR or \fB\s-1SSL_ERROR_WANT_WRITE\s0\fR, it must be repeated
195 with the same arguments.
197 When calling \fISSL_write()\fR with num=0 bytes to be sent the behaviour is
200 .IX Header "RETURN VALUES"
201 The following return values can occur:
204 The write operation was successful, the return value is the number of
205 bytes actually written to the \s-1TLS/SSL\s0 connection.
207 The write operation was not successful. Probably the underlying connection
208 was closed. Call \fISSL_get_error()\fR with the return value \fBret\fR to find out,
209 whether an error occurred or the connection was shut down cleanly
210 (\s-1SSL_ERROR_ZERO_RETURN\s0).
212 SSLv2 (deprecated) does not support a shutdown alert protocol, so it can
213 only be detected, whether the underlying connection was closed. It cannot
214 be checked, why the closure happened.
217 The write operation was not successful, because either an error occurred
218 or action must be taken by the calling process. Call \fISSL_get_error()\fR with the
219 return value \fBret\fR to find out the reason.
221 .IX Header "SEE ALSO"
222 \&\fISSL_get_error\fR\|(3), \fISSL_read\fR\|(3),
223 \&\fISSL_CTX_set_mode\fR\|(3), \fISSL_CTX_new\fR\|(3),
224 \&\fISSL_connect\fR\|(3), \fISSL_accept\fR\|(3)
225 \&\fISSL_set_connect_state\fR\|(3),
226 \&\fIssl\fR\|(3), \fIbio\fR\|(3)