=head1 NAME
-SSL_read_ex, SSL_read - read bytes from a TLS/SSL connection
+SSL_read_ex, SSL_read, SSL_peek_ex, SSL_peek
+- read bytes from a TLS/SSL connection
=head1 SYNOPSIS
#include <openssl/ssl.h>
- int SSL_read_ex(SSL *ssl, void *buf, size_t num, size_t *read);
+ int SSL_read_ex(SSL *ssl, void *buf, size_t num, size_t *readbytes);
int SSL_read(SSL *ssl, void *buf, int num);
- int SSL_peek_ex(SSL *ssl, void *buf, size_t num, size_t *read);
+ int SSL_peek_ex(SSL *ssl, void *buf, size_t num, size_t *readbytes);
int SSL_peek(SSL *ssl, void *buf, int num);
=head1 DESCRIPTION
SSL_read_ex() and SSL_read() try to read B<num> bytes from the specified B<ssl>
into the buffer B<buf>. On success SSL_read_ex() will store the number of bytes
-actually read in B<*read>.
+actually read in B<*readbytes>.
SSL_peek_ex() and SSL_peek() are identical to SSL_read_ex() and SSL_read()
respectively except no bytes are actually removed from the underlying BIO during
functions will return with the bytes buffered. If no more bytes are in the
buffer, the read functions will trigger the processing of the next record.
Only when the record has been received and processed completely will the read
-functions return reporting success. At most the contents of the record will
+functions return reporting success. At most the contents of one 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 the read call
can succeed.
+If B<SSL_MODE_AUTO_RETRY> has been switched off and a non-application data
+record has been processed, the read function can return and set the error to
+B<SSL_ERROR_WANT_READ>.
+In this case there might still be unprocessed data available in the B<BIO>.
+If read ahead was set using L<SSL_CTX_set_read_ahead(3)>, there might also still
+be unprocessed data available in the B<SSL>.
+This behaviour can be controlled using the L<SSL_CTX_set_mode(3)> call.
+
If the underlying BIO is B<blocking>, a read function will only return once the
read operation has been finished or an error occurred, except when a
-renegotiation takes 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)> call.
+non-application data record has been processed and B<SSL_MODE_AUTO_RETRY> is
+not set.
+Note that if B<SSL_MODE_AUTO_RETRY> is set and only non-application data is
+available the call will hang.
If the underlying BIO is B<non-blocking>, a read function will also return when
the underlying BIO could not satisfy the needs of the function to continue the
-operation. In this case a call to L<SSL_get_error(3)> with the
+operation.
+In this case a call to L<SSL_get_error(3)> with the
return value of the read function will yield B<SSL_ERROR_WANT_READ> or
-B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
-a read function can also cause write operations! The calling process then must
-repeat the call after taking appropriate action to satisfy the needs of the read
-function. The action depends on the underlying BIO. When using a 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.
+B<SSL_ERROR_WANT_WRITE>.
+As at any time it's possible that non-application data needs to be sent,
+a read function can also cause write operations.
+The calling process then must repeat the call after taking appropriate action
+to satisfy the needs of the read function.
+The action depends on the underlying BIO.
+When using a 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)> can be used to find out whether there
-are buffered bytes available for immediate retrieval. In this case
-the read function can be called without blocking or actually receiving
-new data from the underlying socket.
-
-=head1 WARNING
-
-When a read function operation has to be repeated because L<SSL_get_error(3)>
-returned B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
-with the same arguments.
+are buffered bytes available for immediate retrieval.
+In this case the read function can be called without blocking or actually
+receiving new data from the underlying socket.
=head1 RETURN VALUES
-SSL_read_ex() and SSL_peek_ex() will return 1 for success or 0 for failure. In
-the event of a failure call SSL_get_error() to find out the reason.
+SSL_read_ex() and SSL_peek_ex() will return 1 for success or 0 for failure.
+Success means that 1 or more application data bytes have been read from the SSL
+connection.
+Failure means that no bytes could be read from the SSL connection.
+Failures can be retryable (e.g. we are waiting for more bytes to
+be delivered by the network) or non-retryable (e.g. a fatal network error).
+In the event of a failure call L<SSL_get_error(3)> to find out the reason which
+indicates whether the call is retryable or not.
For SSL_read() and SSL_peek() the following return values can occur:
=over 4
-=item E<gt>0
+=item E<gt> 0
-The read operation was successful; the return value is the number of
-bytes actually read from the TLS/SSL connection.
+The read operation was successful.
+The return value is the number of bytes actually read from the TLS/SSL
+connection.
-=item Z<>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)>,
-L<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, because either the connection was closed,
+an error occurred or action must be taken by the calling process.
+Call L<SSL_get_error(3)> with the return value B<ret> to find out the reason.
-=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
-return value B<ret> to find out the reason.
+Old documentation indicated a difference between 0 and -1, and that -1 was
+retryable.
+You should instead call SSL_get_error() to find out if it's retryable.
=back
L<SSL_set_connect_state(3)>,
L<SSL_pending(3)>,
L<SSL_shutdown(3)>, L<SSL_set_shutdown(3)>,
-L<ssl(3)>, L<bio(3)>
+L<ssl(7)>, L<bio(7)>
+
+=head1 HISTORY
+
+The SSL_read_ex() and SSL_peek_ex() functions were added in OpenSSL 1.1.1.
=head1 COPYRIGHT
-Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
+Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
-Licensed under the OpenSSL license (the "License"). You may not use
+Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.
projects / openssl.git / blobdiff