openssl/doc/ssl/SSL_pending.pod

=pod

=head1 NAME

SSL_pending, SSL_has_pending - check for readable bytes buffered in an
SSL object

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 int SSL_pending(const SSL *ssl);
 int SSL_has_pending(const SSL *s);

=head1 DESCRIPTION

Data is received in whole blocks known as records from the peer. A whole record
is processed (e.g. decrypted) in one go and is buffered by OpenSSL until it is
read by the application via a call to L<SSL_read(3)>.

SSL_pending() returns the number of bytes which have been processed, buffered
and are available inside B<ssl> for immediate read.

If the B<SSL> object's I<read_ahead> flag is set (see
L<SSL_CTX_set_read_ahead(3)>), additional protocol bytes (beyond the current
record) may have been read containing more TLS/SSL records. This also applies to
DTLS and pipelining (see L<SSL_CTX_set_split_send_fragment(3)>). These
additional bytes will be buffered by OpenSSL but will remain unprocessed until
they are needed. As these bytes are still in an unprocessed state SSL_pending()
will ignore them. Therefore it is possible for no more bytes to be readable from
the underlying BIO (because OpenSSL has already read them) and for SSL_pending()
to return 0, even though readable application data bytes are available (because
the data is in unprocessed buffered records).

SSL_has_pending() returns 1 if B<s> has buffered data (whether processed or
unprocessed) and 0 otherwise. Note that it is possible for SSL_has_pending() to
return 1, and then a subsequent call to SSL_read() to return no data because the
unprocessed buffered data when processed yielded no application data (for
example this can happen during renegotiation). It is also possible in this
scenario for SSL_has_pending() to continue to return 1 even after an SSL_read()
call because the buffered and unprocessed data is not yet processable (e.g.
because OpenSSL has only received a partial record so far).

=head1 RETURN VALUES

SSL_pending() returns the number of buffered and processed application data
bytes that are pending and are available for immediate read. SSL_has_pending()
returns 1 if there is buffered record data in the SSL object and 0 otherwise.

=head1 SEE ALSO

L<SSL_read(3)>, L<SSL_CTX_set_read_ahead(3)>,
L<SSL_CTX_set_split_send_fragment(3)>, L<ssl(3)>

=head1 HISTORY

The SSL_has_pending() function was added in OpenSSL 1.1.0.

=head1 COPYRIGHT

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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>.

=cut