5 SSL_write - write bytes to a TLS/SSL connection.
9 #include <openssl/ssl.h>
11 int SSL_write(SSL *ssl, const void *buf, int num);
15 SSL_write() writes B<num> bytes from the buffer B<buf> into the specified
20 If necessary, SSL_write() will negotiate a TLS/SSL session, if
21 not already explicitly performed by L<SSL_connect(3)|SSL_connect(3)> or
22 L<SSL_accept(3)|SSL_accept(3)>. If the
23 peer requests a re-negotiation, it will be performed transparently during
24 the SSL_write() operation. The behaviour of SSL_write() depends on the
27 For the transparent negotiation to succeed, the B<ssl> must have been
28 initialized to client or server mode. This is not the case if a generic
29 method is being used (see L<SSL_CTX_new(3)|SSL_CTX_new(3)>, so that
30 L<SSL_set_connect_state(3)|SSL_set_connect_state(3)> or SSL_set_accept_state()
31 must be used before the first call to an L<SSL_read(3)|SSL_read(3)>
32 or SSL_write() function.
34 If the underlying BIO is B<blocking>, SSL_write() will only return, once the
35 write operation has been finished or an error occurred, except when a
36 renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur.
37 This behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the
38 L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> call.
40 If the underlying BIO is B<non-blocking>, SSL_write() will also return,
41 when the underlying BIO could not satisfy the needs of SSL_write()
42 to continue the operation. In this case a call to
43 L<SSL_get_error(3)|SSL_get_error(3)> with the
44 return value of SSL_write() will yield B<SSL_ERROR_WANT_READ> or
45 B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
46 call to SSL_write() can also cause read operations! The calling process
47 then must repeat the call after taking appropriate action to satisfy the
48 needs of SSL_write(). The action depends on the underlying BIO. When using a
49 non-blocking socket, nothing is to be done, but select() can be used to check
50 for the required condition. When using a buffering BIO, like a BIO pair, data
51 must be written into or retrieved out of the BIO before being able to continue.
53 SSL_write() will only return with success, when the complete contents
54 of B<buf> of length B<num> has been written. This default behaviour
55 can be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of
56 L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>. When this flag is set,
57 SSL_write() will also return with success, when a partial write has been
58 successfully completed. In this case the SSL_write() operation is considered
59 completed. The bytes are sent and a new SSL_write() operation with a new
60 buffer (with the already sent bytes removed) must be started.
61 A partial write is performed with the size of a message block, which is
66 When an SSL_write() operation has to be repeated because of
67 B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
68 with the same arguments.
72 The following return values can occur:
78 The write operation was successful, the return value is the number of
79 bytes actually written to the TLS/SSL connection.
83 The write operation was not successful. Call SSL_get_error() with the return
84 value B<ret> to find out, whether an error occurred.
88 The write operation was not successful, because either an error occurred
89 or action must be taken by the calling process. Call SSL_get_error() with the
90 return value B<ret> to find out the reason.
96 L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_read(3)|SSL_read(3)>,
97 L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)|SSL_CTX_new(3)>,
98 L<SSL_connect(3)|SSL_connect(3)>, L<SSL_accept(3)|SSL_accept(3)>
99 L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>,
100 L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>