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