SSL_pending() returns the number of bytes which are available inside
ssl for immediate read.
NOTES
Data are received in blocks from the peer. Therefore data can be buffered
inside ssl and are ready for immediate retrieval with
SSL_read(3).
RETURN VALUES
The number of bytes pending is returned.
BUGS
SSL_pending() takes into account only bytes from the TLS/SSL record
that is currently being processed (if any). If the SSL object's
read_ahead flag is set, additional protocol bytes may have been
read containing more TLS/SSL records; these are ignored by
SSL_pending().
Up to OpenSSL 0.9.6, SSL_pending() does not check if the record type
of pending data is application data.
