man SSL_pending () - obtain number of readable bytes buffered in an SSL object
NAME
SSL_pending - obtain number of readable bytes buffered in an SSL object
SYNOPSIS
#include <openssl/ssl.h>
int SSL_pending(const SSL *ssl);
DESCRIPTION
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.