5 SSL_read - read bytes from a TLS/SSL connection.
9 #include <openssl/ssl.h>
11 int SSL_read(SSL *ssl, void *buf, int num);
15 SSL_read() tries to read B<num> bytes from the specified B<ssl> into the
20 If necessary, SSL_read() will negotiate a TLS/SSL session, if
21 not already explicitly performed by L<SSL_connect(3)|SSL_connect(3)> or
22 L<SSL_accept(3)|SSL_accept(3)>. If the
23 peer requests a re-negotiation, it will be performed transparently during
24 the SSL_read() operation. The behaviour of SSL_read() depends on the
27 For the transparent negotiation to succeed, the B<ssl> must have been
28 initialized to client or server mode. This is not the case if a generic
29 method is being used (see L<SSL_CTX_new(3)|SSL_CTX_new(3)>, so that
30 L<SSL_set_connect_state(3)|SSL_set_connect_state(3)> or SSL_set_accept_state()
31 must be used before the first call to an SSL_read() or
32 L<SSL_write(3)|SSL_write(3)> function.
34 If the underlying BIO is B<blocking>, SSL_read() will only return, once the
35 read operation has been finished or an error occurred, except when a
36 renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur.
37 This behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the
38 L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> call.
40 If the underlying BIO is B<non-blocking>, SSL_read() will also return
41 when the underlying BIO could not satisfy the needs of SSL_read()
42 to continue the operation. In this case a call to
43 L<SSL_get_error(3)|SSL_get_error(3)> with the
44 return value of SSL_read() will yield B<SSL_ERROR_WANT_READ> or
45 B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
46 call to SSL_read() can also cause write operations! The calling process
47 then must repeat the call after taking appropriate action to satisfy the
48 needs of SSL_read(). The action depends on the underlying BIO. When using a
49 non-blocking socket, nothing is to be done, but select() can be used to check
50 for the required condition. When using a buffering BIO, like a BIO pair, data
51 must be written into or retrieved out of the BIO before being able to continue.
55 When an SSL_read() operation has to be repeated because of
56 B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
57 with the same arguments.
61 The following return values can occur:
67 The read operation was successful; the return value is the number of
68 bytes actually read from the TLS/SSL connection.
72 The read operation was not successful, probably because no data was
73 available. Call SSL_get_error() with the return value B<ret> to find out,
74 whether an error occurred.
78 The read operation was not successful, because either an error occurred
79 or action must be taken by the calling process. Call SSL_get_error() with the
80 return value B<ret> to find out the reason.
86 L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_write(3)|SSL_write(3)>,
87 L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)|SSL_CTX_new(3)>,
88 L<SSL_connect(3)|SSL_connect(3)>, L<SSL_accept(3)|SSL_accept(3)>
89 L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>,
90 L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>