5 SSL_read - read bytes from a TLS/SSL connection.
9 #include <openssl/ssl.h>
11 int SSL_read(SSL *ssl, char *buf, int num);
15 SSL_read() tries to read B<num> bytes from the specified B<ssl> into the
16 buffer B<buf>. If necessary, SSL_read() will negotiate a TLS/SSL session, if
17 not already explicitly performed by SSL_connect() or SSL_accept(). If the
18 peer requests a re-negotiation, it will be performed transparently during
19 the SSL_read() operation. The behaviour of SSL_read() depends on the
22 If the underlying BIO is B<blocking>, SSL_read() will only return, once the
23 read operation has been finished or an error occurred.
25 If the underlying BIO is B<non-blocking>, SSL_read() will also return
26 when the underlying BIO could not satisfy the needs of SSL_read()
27 to continue the operation. In this case a call to SSL_get_error() with the
28 return value of SSL_read() will yield B<SSL_ERROR_WANT_READ> or
29 B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
30 call to SSL_read() can also cause write operations! The calling process
31 then must repeat the call after taking appropriate action to satisfy the
32 needs of SSL_read(). The action depends on the underlying BIO. When using a
33 non-blocking socket, nothing is to be done, but select() can be used to check
34 for the required condition. When using a buffering BIO, like a BIO pair, data
35 must be written into or retrieved out of the BIO before being able to continue.
39 The following return values can occur:
45 The read operation was successful; the return value is the number of
46 bytes actually read from the TLS/SSL connection.
50 The read operation was not successful, probably because no data was
51 available. Call SSL_get_error() with the return value B<ret> to find out,
52 whether an error occurred.
56 The read operation was not successful, because either an error occurred
57 or action must be taken by the calling process. Call SSL_get_error() with the
58 return value B<ret> to find out the reason.
64 L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_write(3)|SSL_write(3)>,
65 L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>