mirror of
https://github.com/openssl/openssl.git
synced 2024-12-21 06:09:35 +08:00
185 lines
6.0 KiB
Plaintext
185 lines
6.0 KiB
Plaintext
=pod
|
|
|
|
=head1 NAME
|
|
|
|
COMP_CTX_new,
|
|
COMP_CTX_get_method,
|
|
COMP_CTX_get_type,
|
|
COMP_get_type,
|
|
COMP_get_name,
|
|
COMP_CTX_free,
|
|
COMP_compress_block,
|
|
COMP_expand_block,
|
|
COMP_zlib,
|
|
COMP_zlib_oneshot,
|
|
COMP_brotli,
|
|
COMP_brotli_oneshot,
|
|
COMP_zstd,
|
|
COMP_zstd_oneshot,
|
|
BIO_f_zlib,
|
|
BIO_f_brotli,
|
|
BIO_f_zstd
|
|
- Compression support
|
|
|
|
=head1 SYNOPSIS
|
|
|
|
#include <openssl/comp.h>
|
|
|
|
COMP_CTX *COMP_CTX_new(COMP_METHOD *meth);
|
|
void COMP_CTX_free(COMP_CTX *ctx);
|
|
const COMP_METHOD *COMP_CTX_get_method(const COMP_CTX *ctx);
|
|
int COMP_CTX_get_type(const COMP_CTX* comp);
|
|
int COMP_get_type(const COMP_METHOD *meth);
|
|
const char *COMP_get_name(const COMP_METHOD *meth);
|
|
|
|
int COMP_compress_block(COMP_CTX *ctx, unsigned char *out, int olen,
|
|
unsigned char *in, int ilen);
|
|
int COMP_expand_block(COMP_CTX *ctx, unsigned char *out, int olen,
|
|
unsigned char *in, int ilen);
|
|
|
|
COMP_METHOD *COMP_zlib(void);
|
|
COMP_METHOD *COMP_zlib_oneshot(void);
|
|
COMP_METHOD *COMP_brotli(void);
|
|
COMP_METHOD *COMP_brotli_oneshot(void);
|
|
COMP_METHOD *COMP_zstd(void);
|
|
COMP_METHOD *COMP_zstd_oneshot(void);
|
|
|
|
const BIO_METHOD *BIO_f_zlib(void);
|
|
const BIO_METHOD *BIO_f_brotli(void);
|
|
const BIO_METHOD *BIO_f_zstd(void);
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
These functions provide compression support for OpenSSL. Compression is used within
|
|
the OpenSSL library to support TLS record and certificate compression.
|
|
|
|
COMP_CTX_new() is used to create a new B<COMP_CTX> structure used to compress data.
|
|
|
|
COMP_CTX_free() is used to free the returned B<COMP_CTX>.
|
|
If the argument is NULL, nothing is done.
|
|
|
|
COMP_CTX_get_method() returns the B<COMP_METHOD> of the given I<ctx>.
|
|
|
|
COMP_CTX_get_type() and COMP_get_type() return the NID for the B<COMP_CTX> and
|
|
B<COMP_METHOD>, respectively. COMP_get_name() returns the name of the algorithm
|
|
of the given B<COMP_METHOD>.
|
|
|
|
COMP_compress_block() compresses b<ilen> bytes from the buffer I<in> into the
|
|
buffer b<out> of size I<olen> using the algorithm specified by I<ctx>.
|
|
|
|
COMP_expand_block() expands I<ilen> bytes from the buffer I<in> into the
|
|
buffer I<out> of size I<olen> using the algorithm specified by I<ctx>.
|
|
|
|
Methods (B<COMP_METHOD>) may be specified by one of these functions. These functions
|
|
will be available even if their corresponding compression algorithm is not configured
|
|
into the OpenSSL library. In such a case, NULL will be returned.
|
|
|
|
=over 4
|
|
|
|
=item *
|
|
|
|
COMP_zlib() returns a B<COMP_METHOD> for stream-based ZLIB compression.
|
|
|
|
=item *
|
|
|
|
COMP_zlib_oneshot() returns a B<COMP_METHOD> for one-shot ZLIB compression.
|
|
|
|
=item *
|
|
|
|
COMP_brotli() returns a B<COMP_METHOD> for stream-based Brotli compression.
|
|
|
|
=item *
|
|
|
|
COMP_brotli_oneshot() returns a B<COMP_METHOD> for one-shot Brotli compression.
|
|
|
|
=item *
|
|
|
|
COMP_zstd() returns a B<COMP_METHOD> for stream-based Zstandard compression.
|
|
|
|
=item *
|
|
|
|
COMP_zstd_oneshot() returns a B<COMP_METHOD> for one-shot Zstandard compression.
|
|
|
|
=back
|
|
|
|
BIO_f_zlib(), BIO_f_brotli() BIO_f_zstd() each return a B<BIO_METHOD> that may be used to
|
|
create a B<BIO> via B<BIO_new(3)> to read and write compressed files or streams.
|
|
The functions are only available if the corresponding algorithm is compiled into
|
|
the OpenSSL library. NULL may be returned if the algorithm fails to load dynamically.
|
|
|
|
=head1 NOTES
|
|
|
|
While compressing non-compressible data, the output may be larger than the
|
|
input. Care should be taken to size output buffers appropriate for both
|
|
compression and expansion.
|
|
|
|
Compression support and compression algorithms must be enabled and built into
|
|
the library before use. Refer to the INSTALL.md file when configuring OpenSSL.
|
|
|
|
ZLIB may be found at L<https://zlib.net>
|
|
|
|
Brotli may be found at L<https://github.com/google/brotli>.
|
|
|
|
Zstandard may be found at L<https://github.com/facebook/zstd>.
|
|
|
|
Compression of SSL/TLS records is not recommended, as it has been
|
|
shown to lead to the CRIME attack L<https://en.wikipedia.org/wiki/CRIME>.
|
|
It is disabled by default, and may be enabled by clearing the
|
|
SSL_OP_NO_COMPRESSION option and setting the security level as appropriate.
|
|
See the documentation for the L<SSL_CTX_set_options(3)> and
|
|
L<SSL_set_options(3)> functions.
|
|
|
|
Compression is also used to support certificate compression as described
|
|
in RFC8879 L<https://datatracker.ietf.org/doc/html/rfc8879>.
|
|
It may be disabled via the SSL_OP_NO_TX_CERTIFICATE_COMPRESSION and
|
|
SSL_OP_NO_RX_CERTIFICATE_COMPRESSION options of the
|
|
L<SSL_CTX_set_options(3)> or L<SSL_set_options(3)> functions.
|
|
|
|
COMP_zlib(), COMP_brotli() and COMP_zstd() are stream-based compression methods.
|
|
Internal state (including compression dictionary) is maintained between calls.
|
|
If an error is returned, the stream is corrupted, and should be closed.
|
|
|
|
COMP_zlib_oneshot(), COMP_brotli_oneshot() and COMP_zstd_oneshot() are not stream-based. These
|
|
methods do not maintain state between calls. An error in one call does not affect
|
|
future calls.
|
|
|
|
=head1 RETURN VALUES
|
|
|
|
COMP_CTX_new() returns a B<COMP_CTX> on success, or NULL on failure.
|
|
|
|
COMP_CTX_get_method(), COMP_zlib(), COMP_zlib_oneshot(), COMP_brotli(), COMP_brotli_oneshot(),
|
|
COMP_zstd(), and COMP_zstd_oneshot() return a B<COMP_METHOD> on success,
|
|
or NULL on failure.
|
|
|
|
COMP_CTX_get_type() and COMP_get_type() return a NID value. On failure,
|
|
NID_undef is returned.
|
|
|
|
COMP_compress_block() and COMP_expand_block() return the number of
|
|
bytes stored in the output buffer I<out>. This may be 0. On failure,
|
|
-1 is returned.
|
|
|
|
COMP_get_name() returns a B<const char *> that must not be freed
|
|
on success, or NULL on failure.
|
|
|
|
BIO_f_zlib(), BIO_f_brotli() and BIO_f_zstd() return NULL on error, and
|
|
a B<BIO_METHOD> on success.
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<BIO_new(3)>, L<SSL_CTX_set_options(3)>, L<SSL_set_options(3)>
|
|
|
|
=head1 HISTORY
|
|
|
|
Brotli and Zstandard functions were added in OpenSSL 3.2.
|
|
|
|
=head1 COPYRIGHT
|
|
|
|
Copyright 2022-2024 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
|
|
L<https://www.openssl.org/source/license.html>.
|
|
|
|
=cut
|