Updated: 2021/Apr/14

SSL_pending(3)                      OpenSSL                     SSL_pending(3)

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

       libcrypto, -lcrypto

        #include <openssl/ssl.h>

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

       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
       SSL_read_ex(3) or SSL_read(3).

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

       If the SSL object's read_ahead flag is set (see
       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
       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 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_ex() or 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_ex() or 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).

       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.

       SSL_read_ex(3), SSL_read(3), SSL_CTX_set_read_ahead(3),
       SSL_CTX_set_split_send_fragment(3), ssl(7)

       The SSL_has_pending() function was added in OpenSSL 1.1.0.

       Copyright 2000-2020 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

1.1.1i                            2020-12-10                    SSL_pending(3)