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

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       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
       <https://www.openssl.org/source/license.html>.

3.5.0                                              2025-06-04                                  SSL_PENDING(3SSL)

       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).

       The SSL_has_pending() function was added in OpenSSL 1.1.0.

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

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)

        #include <openssl/ssl.h>

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