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SSL_pending(3) OpenSSL SSL_pending(3)
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SSL_pending, SSL_has_pending - check for readable bytes buffered in an
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),
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)