SSL_read.pod revision 72613 
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, char *buf, int num);
12
13=head1 DESCRIPTION
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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 SSL_connect() or SSL_accept(). If the
22peer requests a re-negotiation, it will be performed transparently during
23the SSL_read() operation. The behaviour of SSL_read() depends on the
24underlying BIO. 
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26If the underlying BIO is B<blocking>, SSL_read() will only return, once the
27read operation has been finished or an error occurred.
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29If the underlying BIO is B<non-blocking>, SSL_read() will also return
30when the underlying BIO could not satisfy the needs of SSL_read()
31to continue the operation. In this case a call to SSL_get_error() with the
32return value of SSL_read() will yield B<SSL_ERROR_WANT_READ> or
33B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
34call to SSL_read() can also cause write operations! The calling process
35then must repeat the call after taking appropriate action to satisfy the
36needs of SSL_read(). The action depends on the underlying BIO. When using a
37non-blocking socket, nothing is to be done, but select() can be used to check
38for the required condition. When using a buffering BIO, like a BIO pair, data
39must be written into or retrieved out of the BIO before being able to continue.
40
41=head1 WARNING
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43When an SSL_read() operation has to be repeated because of
44B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
45with the same arguments.
46
47=head1 RETURN VALUES
48
49The following return values can occur:
50
51=over 4
52
53=item E<gt>0
54
55The read operation was successful; the return value is the number of
56bytes actually read from the TLS/SSL connection.
57
58=item 0
59
60The read operation was not successful, probably because no data was
61available. Call SSL_get_error() with the return value B<ret> to find out,
62whether an error occurred.
63
64=item E<lt>0
65
66The read operation was not successful, because either an error occurred
67or action must be taken by the calling process. Call SSL_get_error() with the
68return value B<ret> to find out the reason.
69
70=back
71
72=head1 SEE ALSO
73
74L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_write(3)|SSL_write(3)>,
75L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>
76
77=cut
78