SSL_write.pod revision 79998
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 not the case if a generic 29method is being used (see L<SSL_CTX_new(3)|SSL_CTX_new(3)>, so that 30L<SSL_set_connect_state(3)|SSL_set_connect_state(3)> or SSL_set_accept_state() 31must be used before the first call to an L<SSL_read(3)|SSL_read(3)> 32or SSL_write() function. 33 34If the underlying BIO is B<blocking>, SSL_write() will only return, once the 35write operation has been finished or an error occurred, except when a 36renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur. 37This behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the 38L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> call. 39 40If the underlying BIO is B<non-blocking>, SSL_write() will also return, 41when the underlying BIO could not satisfy the needs of SSL_write() 42to continue the operation. In this case a call to 43L<SSL_get_error(3)|SSL_get_error(3)> with the 44return value of SSL_write() will yield B<SSL_ERROR_WANT_READ> or 45B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a 46call to SSL_write() can also cause read operations! The calling process 47then must repeat the call after taking appropriate action to satisfy the 48needs of SSL_write(). The action depends on the underlying BIO. When using a 49non-blocking socket, nothing is to be done, but select() can be used to check 50for the required condition. When using a buffering BIO, like a BIO pair, data 51must be written into or retrieved out of the BIO before being able to continue. 52 53SSL_write() will only return with success, when the complete contents 54of B<buf> of length B<num> has been written. This default behaviour 55can be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of 56L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>. When this flag is set, 57SSL_write() will also return with success, when a partial write has been 58successfully completed. In this case the SSL_write() operation is considered 59completed. The bytes are sent and a new SSL_write() operation with a new 60buffer (with the already sent bytes removed) must be started. 61A partial write is performed with the size of a message block, which is 6216kB for SSLv3/TLSv1. 63 64=head1 WARNING 65 66When an SSL_write() operation has to be repeated because of 67B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated 68with the same arguments. 69 70=head1 RETURN VALUES 71 72The following return values can occur: 73 74=over 4 75 76=item E<gt>0 77 78The write operation was successful, the return value is the number of 79bytes actually written to the TLS/SSL connection. 80 81=item 0 82 83The write operation was not successful. Call SSL_get_error() with the return 84value B<ret> to find out, whether an error occurred. 85 86=item E<lt>0 87 88The write operation was not successful, because either an error occurred 89or action must be taken by the calling process. Call SSL_get_error() with the 90return value B<ret> to find out the reason. 91 92=back 93 94=head1 SEE ALSO 95 96L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_read(3)|SSL_read(3)>, 97L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)|SSL_CTX_new(3)>, 98L<SSL_connect(3)|SSL_connect(3)>, L<SSL_accept(3)|SSL_accept(3)> 99L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>, 100L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)> 101 102=cut 103