BIO_f_readbuffer(3)

BIO_f_readbuffer(3) | OpenSSL | BIO_f_readbuffer(3)

# NAME

BIO_f_readbuffer - read only buffering BIO that supports BIO_tell() and BIO_seek()

# SYNOPSIS

     #include <openssl/bio.h>
     const BIO_METHOD *BIO_f_readbuffer(void);

# DESCRIPTION

BIO_f_readbuffer() returns the read buffering BIO method.

This BIO filter can be inserted on top of BIO's that do not support BIO_tell() or BIO_seek() (e.g. A file BIO that uses stdin).

Data read from a read buffering BIO comes from an internal buffer which is filled from the next BIO in the chain.

BIO_gets() is supported for read buffering BIOs. Writing data to a read buffering BIO is not supported.

Calling BIO_reset() on a read buffering BIO does not clear any buffered data.

# NOTES

Read buffering BIOs implement BIO_read_ex() by using BIO_read_ex() operations on the next BIO (e.g. a file BIO) in the chain and storing the result in an internal buffer, from which bytes are given back to the caller as appropriate for the call. BIO_read_ex() is guaranteed to give the caller the number of bytes it asks for, unless there's an error or end of communication is reached in the next BIO. The internal buffer can grow to cache the entire contents of the next BIO in the chain. BIO_seek() uses the internal buffer, so that it can only seek into data that is already read.

# RETURN VALUES

BIO_f_readbuffer() returns the read buffering BIO method.

# SEE ALSO

bio(7), BIO_read(3), BIO_gets(3), BIO_reset(3), BIO_ctrl(3).

# COPYRIGHT

Copyright 2021 The OpenSSL Project Authors. All Rights Reserved.

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>.

2026-04-07 | 3.5.6