SSL_read.pod revision 76866
1=pod 2 3=head1 NAME 4 5SSL_read - read bytes from a TLS/SSL connection. 6 7=head1 SYNOPSIS 8 9 #include <openssl/ssl.h> 10 11 int SSL_read(SSL *ssl, void *buf, int num); 12 13=head1 DESCRIPTION 14 15SSL_read() tries to read B<num> bytes from the specified B<ssl> into the 16buffer B<buf>. 17 18=head1 NOTES 19 20If necessary, SSL_read() 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_read() operation. The behaviour of SSL_read() 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 SSL_read() or 32L<SSL_write(3)|SSL_write(3)> function. 33 34If the underlying BIO is B<blocking>, SSL_read() will only return, once the 35read 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_read() will also return 41when the underlying BIO could not satisfy the needs of SSL_read() 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_read() 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_read() can also cause write operations! The calling process 47then must repeat the call after taking appropriate action to satisfy the 48needs of SSL_read(). 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 53=head1 WARNING 54 55When an SSL_read() operation has to be repeated because of 56B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated 57with the same arguments. 58 59=head1 RETURN VALUES 60 61The following return values can occur: 62 63=over 4 64 65=item E<gt>0 66 67The read operation was successful; the return value is the number of 68bytes actually read from the TLS/SSL connection. 69 70=item 0 71 72The read operation was not successful, probably because no data was 73available. Call SSL_get_error() with the return value B<ret> to find out, 74whether an error occurred. 75 76=item E<lt>0 77 78The read operation was not successful, because either an error occurred 79or action must be taken by the calling process. Call SSL_get_error() with the 80return value B<ret> to find out the reason. 81 82=back 83 84=head1 SEE ALSO 85 86L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_write(3)|SSL_write(3)>, 87L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)|SSL_CTX_new(3)>, 88L<SSL_connect(3)|SSL_connect(3)>, L<SSL_accept(3)|SSL_accept(3)> 89L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>, 90L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)> 91 92=cut 93