Rework section about return values another time (based on hints from

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

diff --git a/doc/ssl/SSL_read.pod b/doc/ssl/SSL_read.pod
index 072dc26cf2843470dd33f93170bbc696a3f29dac..f6c37f77e491d5d39c02a85bdd9922e0bc3e10b4 100644 (file)
--- a/doc/ssl/SSL_read.pod
+++ b/doc/ssl/SSL_read.pod
@@ -8,7 +8,7 @@ SSL_read - read bytes from a TLS/SSL connection.
 
  #include <openssl/ssl.h>
 
 
  #include <openssl/ssl.h>
 

- int SSL_read(SSL *ssl, char *buf, int num);
+ int SSL_read(SSL *ssl, void *buf, int num);

 
 =head1 DESCRIPTION
 
 
 =head1 DESCRIPTION
 


@@ -18,17 +18,43 @@ buffer B<buf>.
 =head1 NOTES
 
 If necessary, SSL_read() will negotiate a TLS/SSL session, if
 =head1 NOTES
 
 If necessary, SSL_read() will negotiate a TLS/SSL session, if

-not already explicitly performed by SSL_connect() or SSL_accept(). If the
+not already explicitly performed by L<SSL_connect(3)|SSL_connect(3)> or
+L<SSL_accept(3)|SSL_accept(3)>. If the

 peer requests a re-negotiation, it will be performed transparently during
 the SSL_read() operation. The behaviour of SSL_read() depends on the
 underlying BIO. 
 
 peer requests a re-negotiation, it will be performed transparently during
 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 being done by calling
+L<SSL_set_connect_state(3)|SSL_set_connect_state(3)> or SSL_set_accept_state()
+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
+record has been completely received, it can be processed (decryption and
+check of integrity). Therefore data that was not retrieved at the last
+call of SSL_read() can still be buffered inside the SSL layer and will be
+retrieved on the next call to SSL_read(). If B<num> is higher than the
+number of bytes buffered, SSL_read() will return with the bytes buffered.
+If no more bytes are in the buffer, SSL_read() will trigger the processing
+of the next record. Only when the record has been received and processed
+completely, SSL_read() will return reporting success. At most the contents
+of the record will be returned. As the size of an SSL/TLS record may exceed
+the maximum packet size of the underlying transport (e.g. TCP), it may
+be necessary to read several packets from the transport layer before the
+record is complete and SSL_read() can succeed.
+

 If the underlying BIO is B<blocking>, SSL_read() will only return, once the
 If the underlying BIO is B<blocking>, SSL_read() will only return, once the

-read operation has been finished or an error occurred.
+read operation has been finished or an error occurred, except when a
+renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur. 
+This behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the
+L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> call.

 
 If the underlying BIO is B<non-blocking>, SSL_read() will also return
 when the underlying BIO could not satisfy the needs of SSL_read()
 
 If the underlying BIO is B<non-blocking>, SSL_read() will also return
 when the underlying BIO could not satisfy the needs of SSL_read()

-to continue the operation. In this case a call to SSL_get_error() with the
+to continue the operation. In this case a call to
+L<SSL_get_error(3)|SSL_get_error(3)> with the

 return value of SSL_read() will yield B<SSL_ERROR_WANT_READ> or
 B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
 call to SSL_read() can also cause write operations! The calling process
 return value of SSL_read() will yield B<SSL_ERROR_WANT_READ> or
 B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
 call to SSL_read() can also cause write operations! The calling process


@@ -57,11 +83,22 @@ bytes actually read from the TLS/SSL connection.
 
 =item 0
 
 
 =item 0
 

-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.
+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).
+
+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 -1
+=item E<lt>0

 
 The read operation was not successful, because either an error occurred
 or action must be taken by the calling process. Call SSL_get_error() with the
 
 The read operation was not successful, because either an error occurred
 or action must be taken by the calling process. Call SSL_get_error() with the


@@ -72,6 +109,10 @@ return value B<ret> to find out the reason.
 =head1 SEE ALSO
 
 L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_write(3)|SSL_write(3)>,
 =head1 SEE ALSO
 
 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_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
 L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>
 
 =cut