mirror of
https://github.com/nillerusr/source-engine.git
synced 2024-12-28 09:03:01 +00:00
125 lines
5.0 KiB
Plaintext
125 lines
5.0 KiB
Plaintext
=pod
|
|
|
|
=head1 NAME
|
|
|
|
SSL_read - read bytes from a TLS/SSL connection.
|
|
|
|
=head1 SYNOPSIS
|
|
|
|
#include <openssl/ssl.h>
|
|
|
|
int SSL_read(SSL *ssl, void *buf, int num);
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
SSL_read() tries to read B<num> bytes from the specified B<ssl> into the
|
|
buffer B<buf>.
|
|
|
|
=head1 NOTES
|
|
|
|
If necessary, SSL_read() will negotiate a TLS/SSL session, if
|
|
not already explicitly performed by L<SSL_connect(3)|SSL_connect(3)> or
|
|
L<SSL_accept(3)|SSL_accept(3)>. If the
|
|
peer requests a re-negotiation, it will be performed transparently during
|
|
the SSL_read() operation. The behaviour of SSL_read() depends on the
|
|
underlying BIO.
|
|
|
|
For the transparent negotiation to succeed, the B<ssl> must have been
|
|
initialized to client or server mode. This is being done by calling
|
|
L<SSL_set_connect_state(3)|SSL_set_connect_state(3)> or SSL_set_accept_state()
|
|
before the first call to an SSL_read() or L<SSL_write(3)|SSL_write(3)>
|
|
function.
|
|
|
|
SSL_read() works based on the SSL/TLS records. The data are received in
|
|
records (with a maximum record size of 16kB for SSLv3/TLSv1). Only when a
|
|
record has been completely received, it can be processed (decryption and
|
|
check of integrity). Therefore data that was not retrieved at the last
|
|
call of SSL_read() can still be buffered inside the SSL layer and will be
|
|
retrieved on the next call to SSL_read(). If B<num> is higher than the
|
|
number of bytes buffered, SSL_read() will return with the bytes buffered.
|
|
If no more bytes are in the buffer, SSL_read() will trigger the processing
|
|
of the next record. Only when the record has been received and processed
|
|
completely, SSL_read() will return reporting success. At most the contents
|
|
of the record will be returned. As the size of an SSL/TLS record may exceed
|
|
the maximum packet size of the underlying transport (e.g. TCP), it may
|
|
be necessary to read several packets from the transport layer before the
|
|
record is complete and SSL_read() can succeed.
|
|
|
|
If the underlying BIO is B<blocking>, SSL_read() will only return, once the
|
|
read operation has been finished or an error occurred, except when a
|
|
renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur.
|
|
This behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the
|
|
L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> call.
|
|
|
|
If the underlying BIO is B<non-blocking>, SSL_read() will also return
|
|
when the underlying BIO could not satisfy the needs of SSL_read()
|
|
to continue the operation. In this case a call to
|
|
L<SSL_get_error(3)|SSL_get_error(3)> with the
|
|
return value of SSL_read() will yield B<SSL_ERROR_WANT_READ> or
|
|
B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
|
|
call to SSL_read() can also cause write operations! The calling process
|
|
then must repeat the call after taking appropriate action to satisfy the
|
|
needs of SSL_read(). The action depends on the underlying BIO. When using a
|
|
non-blocking socket, nothing is to be done, but select() can be used to check
|
|
for the required condition. When using a buffering BIO, like a BIO pair, data
|
|
must be written into or retrieved out of the BIO before being able to continue.
|
|
|
|
L<SSL_pending(3)|SSL_pending(3)> can be used to find out whether there
|
|
are buffered bytes available for immediate retrieval. In this case
|
|
SSL_read() can be called without blocking or actually receiving new
|
|
data from the underlying socket.
|
|
|
|
=head1 WARNING
|
|
|
|
When an SSL_read() operation has to be repeated because of
|
|
B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
|
|
with the same arguments.
|
|
|
|
=head1 RETURN VALUES
|
|
|
|
The following return values can occur:
|
|
|
|
=over 4
|
|
|
|
=item E<gt>0
|
|
|
|
The read operation was successful; the return value is the number of
|
|
bytes actually read from the TLS/SSL connection.
|
|
|
|
=item Z<>0
|
|
|
|
The read operation was not successful. The reason may either be a clean
|
|
shutdown due to a "close notify" alert sent by the peer (in which case
|
|
the SSL_RECEIVED_SHUTDOWN flag in the ssl shutdown state is set
|
|
(see L<SSL_shutdown(3)|SSL_shutdown(3)>,
|
|
L<SSL_set_shutdown(3)|SSL_set_shutdown(3)>). It is also possible, that
|
|
the peer simply shut down the underlying transport and the shutdown is
|
|
incomplete. Call SSL_get_error() with the return value B<ret> to find out,
|
|
whether an error occurred or the connection was shut down cleanly
|
|
(SSL_ERROR_ZERO_RETURN).
|
|
|
|
SSLv2 (deprecated) does not support a shutdown alert protocol, so it can
|
|
only be detected, whether the underlying connection was closed. It cannot
|
|
be checked, whether the closure was initiated by the peer or by something
|
|
else.
|
|
|
|
=item E<lt>0
|
|
|
|
The read operation was not successful, because either an error occurred
|
|
or action must be taken by the calling process. Call SSL_get_error() with the
|
|
return value B<ret> to find out the reason.
|
|
|
|
=back
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_write(3)|SSL_write(3)>,
|
|
L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)|SSL_CTX_new(3)>,
|
|
L<SSL_connect(3)|SSL_connect(3)>, L<SSL_accept(3)|SSL_accept(3)>
|
|
L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>,
|
|
L<SSL_pending(3)|SSL_pending(3)>,
|
|
L<SSL_shutdown(3)|SSL_shutdown(3)>, L<SSL_set_shutdown(3)|SSL_set_shutdown(3)>,
|
|
L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>
|
|
|
|
=cut
|