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)> or
22 L<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 being done by calling
29 L<SSL_set_connect_state(3)> or SSL_set_accept_state()
30 before the first call to an L<SSL_read(3)> or SSL_write() function.
32 If the underlying BIO is B<blocking>, SSL_write() will only return, once the
33 write operation has been finished or an error occurred, except when a
34 renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur.
35 This behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the
36 L<SSL_CTX_set_mode(3)> call.
38 If the underlying BIO is B<non-blocking>, SSL_write() will also return,
39 when the underlying BIO could not satisfy the needs of SSL_write()
40 to continue the operation. In this case a call to
41 L<SSL_get_error(3)> with the
42 return value of SSL_write() will yield B<SSL_ERROR_WANT_READ> or
43 B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
44 call to SSL_write() can also cause read operations! The calling process
45 then must repeat the call after taking appropriate action to satisfy the
46 needs of SSL_write(). The action depends on the underlying BIO. When using a
47 non-blocking socket, nothing is to be done, but select() can be used to check
48 for the required condition. When using a buffering BIO, like a BIO pair, data
49 must be written into or retrieved out of the BIO before being able to continue.
51 SSL_write() will only return with success, when the complete contents
52 of B<buf> of length B<num> has been written. This default behaviour
53 can be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of
54 L<SSL_CTX_set_mode(3)>. When this flag is set,
55 SSL_write() will also return with success, when a partial write has been
56 successfully completed. In this case the SSL_write() operation is considered
57 completed. The bytes are sent and a new SSL_write() operation with a new
58 buffer (with the already sent bytes removed) must be started.
59 A partial write is performed with the size of a message block, which is
64 When an SSL_write() operation has to be repeated because of
65 B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
66 with the same arguments.
68 When calling SSL_write() with num=0 bytes to be sent the behaviour is
73 The following return values can occur:
79 The write operation was successful, the return value is the number of
80 bytes actually written to the TLS/SSL connection.
84 The write operation was not successful. Probably the underlying connection
85 was closed. Call SSL_get_error() with the return value B<ret> to find out,
86 whether an error occurred or the connection was shut down cleanly
87 (SSL_ERROR_ZERO_RETURN).
91 The write operation was not successful, because either an error occurred
92 or action must be taken by the calling process. Call SSL_get_error() with the
93 return value B<ret> to find out the reason.
99 L<SSL_get_error(3)>, L<SSL_read(3)>,
100 L<SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)>,
101 L<SSL_connect(3)>, L<SSL_accept(3)>
102 L<SSL_set_connect_state(3)>,