- NAME
- SYNOPSIS
- DESCRIPTION
- NOTES
- RETURN VALUES
- SEE ALSO
- COPYRIGHT

# NAME

SSL_CTX_set_read_ahead, SSL_CTX_get_read_ahead, SSL_set_read_ahead, SSL_get_read_ahead, SSL_CTX_get_default_read_ahead - manage whether to read as many input bytes as possible

# SYNOPSIS

     #include <openssl/ssl.h>

     void SSL_set_read_ahead(SSL *s, int yes);
     int SSL_get_read_ahead(const SSL *s);

     SSL_CTX_set_read_ahead(SSL_CTX *ctx, int yes);
     long SSL_CTX_get_read_ahead(SSL_CTX *ctx);
     long SSL_CTX_get_default_read_ahead(SSL_CTX *ctx);

# DESCRIPTION

`SSL_CTX_set_read_ahead()` and `SSL_set_read_ahead()` set whether we should read as many input bytes as possible (for non-blocking reads) or not. For example if x bytes are currently required by OpenSSL, but y bytes are available from the underlying BIO (where y > x), then OpenSSL will read all y bytes into its buffer (providing that the buffer is large enough) if reading ahead is on, or x bytes otherwise. Setting the parameter yes to 0 turns reading ahead is off, other values turn it on. `SSL_CTX_set_default_read_ahead()` is identical to `SSL_CTX_set_read_ahead()`.

`SSL_CTX_get_read_ahead()` and `SSL_get_read_ahead()` indicate whether reading ahead has been set or not. `SSL_CTX_get_default_read_ahead()` is identical to `SSL_CTX_get_read_ahead()`.

# NOTES

These functions have no impact when used with DTLS. The return values for `SSL_CTX_get_read_head()` and `SSL_get_read_ahead()` are undefined for DTLS. Setting read_ahead can impact the behaviour of the `SSL_pending()` function (see SSL_pending(3)).

Since `SSL_read()` can return SSL_ERROR_WANT_READ for non-application data records, and `SSL_has_pending()` can't tell the difference between processed and unprocessed data, it's recommended that if read ahead is turned on that SSL_MODE_AUTO_RETRY is not turned off using `SSL_CTX_clear_mode()`. That will prevent getting SSL_ERROR_WANT_READ when there is still a complete record available that hasn't been processed.

If the application wants to continue to use the underlying transport (e.g. TCP connection) after the SSL connection is finished using `SSL_shutdown()` reading ahead should be turned off. Otherwise the SSL structure might read data that it shouldn't.

# RETURN VALUES

`SSL_get_read_ahead()` and `SSL_CTX_get_read_ahead()` return 0 if reading ahead is off, and non zero otherwise.

# SEE ALSO

ssl(7), SSL_pending(3)

# COPYRIGHT

Copyright 2015-2019 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 https://www.openssl.org/source/license.html.