SSL_write.pod revision 303975
1=pod 2 3=head1 NAME 4 5SSL_write - write bytes to a TLS/SSL connection. 6 7=head1 SYNOPSIS 8 9 #include <openssl/ssl.h> 10 11 int SSL_write(SSL *ssl, const void *buf, int num); 12 13=head1 DESCRIPTION 14 15SSL_write() writes B<num> bytes from the buffer B<buf> into the specified 16B<ssl> connection. 17 18=head1 NOTES 19 20If necessary, SSL_write() will negotiate a TLS/SSL session, if 21not already explicitly performed by L<SSL_connect(3)|SSL_connect(3)> or 22L<SSL_accept(3)|SSL_accept(3)>. If the 23peer requests a re-negotiation, it will be performed transparently during 24the SSL_write() operation. The behaviour of SSL_write() depends on the 25underlying BIO. 26 27For the transparent negotiation to succeed, the B<ssl> must have been 28initialized to client or server mode. This is being done by calling 29L<SSL_set_connect_state(3)|SSL_set_connect_state(3)> or SSL_set_accept_state() 30before the first call to an L<SSL_read(3)|SSL_read(3)> or SSL_write() function. 31 32If the underlying BIO is B<blocking>, SSL_write() will only return, once the 33write operation has been finished or an error occurred, except when a 34renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur. 35This behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the 36L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> call. 37 38If the underlying BIO is B<non-blocking>, SSL_write() will also return, 39when the underlying BIO could not satisfy the needs of SSL_write() 40to continue the operation. In this case a call to 41L<SSL_get_error(3)|SSL_get_error(3)> with the 42return value of SSL_write() will yield B<SSL_ERROR_WANT_READ> or 43B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a 44call to SSL_write() can also cause read operations! The calling process 45then must repeat the call after taking appropriate action to satisfy the 46needs of SSL_write(). The action depends on the underlying BIO. When using a 47non-blocking socket, nothing is to be done, but select() can be used to check 48for the required condition. When using a buffering BIO, like a BIO pair, data 49must be written into or retrieved out of the BIO before being able to continue. 50 51SSL_write() will only return with success, when the complete contents 52of B<buf> of length B<num> has been written. This default behaviour 53can be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of 54L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>. When this flag is set, 55SSL_write() will also return with success, when a partial write has been 56successfully completed. In this case the SSL_write() operation is considered 57completed. The bytes are sent and a new SSL_write() operation with a new 58buffer (with the already sent bytes removed) must be started. 59A partial write is performed with the size of a message block, which is 6016kB for SSLv3/TLSv1. 61 62=head1 WARNING 63 64When an SSL_write() operation has to be repeated because of 65B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated 66with the same arguments. 67 68When calling SSL_write() with num=0 bytes to be sent the behaviour is 69undefined. 70 71=head1 RETURN VALUES 72 73The following return values can occur: 74 75=over 4 76 77=item E<gt>0 78 79The write operation was successful, the return value is the number of 80bytes actually written to the TLS/SSL connection. 81 82=item Z<>0 83 84The write operation was not successful. Probably the underlying connection 85was closed. Call SSL_get_error() with the return value B<ret> to find out, 86whether an error occurred or the connection was shut down cleanly 87(SSL_ERROR_ZERO_RETURN). 88 89SSLv2 (deprecated) does not support a shutdown alert protocol, so it can 90only be detected, whether the underlying connection was closed. It cannot 91be checked, why the closure happened. 92 93=item E<lt>0 94 95The write operation was not successful, because either an error occurred 96or action must be taken by the calling process. Call SSL_get_error() with the 97return value B<ret> to find out the reason. 98 99=back 100 101=head1 SEE ALSO 102 103L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_read(3)|SSL_read(3)>, 104L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)|SSL_CTX_new(3)>, 105L<SSL_connect(3)|SSL_connect(3)>, L<SSL_accept(3)|SSL_accept(3)> 106L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>, 107L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)> 108 109=cut 110