More complete X509_check_host documentation.

[openssl.git] / doc / ssl / SSL_read.pod

diff --git a/doc/ssl/SSL_read.pod b/doc/ssl/SSL_read.pod
index cc7aa1a5476639adcfba3ff8623bafcad12b832b..8ca0ce5058da0e5f1299e16d559067e5983737d8 100644 (file)
--- a/doc/ssl/SSL_read.pod
+++ b/doc/ssl/SSL_read.pod
@@ -25,11 +25,10 @@ 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 not the case if a generic
-method is being used (see L<SSL_CTX_new(3)|SSL_CTX_new(3)>, so that
+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()
-must be used before the first call to an SSL_read() or
-L<SSL_write(3)|SSL_write(3)> function).
+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
@@ -65,6 +64,11 @@ 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
@@ -82,11 +86,22 @@ The following return values can occur:
 The read operation was successful; the return value is the number of
 bytes actually read from the TLS/SSL connection.
 
-=item 0
+=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).
 
-The read operation was not successful, probably because no data was
-available. Call SSL_get_error() with the return value B<ret> to find out,
-whether an error occurred.
+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
 
@@ -102,6 +117,8 @@ 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