Co-authored-by: Alejandro Colomar <alx@kernel.org>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

This adds two helper function that will be used in subsequent commits.

nxt_http_comp_compress() does the actual compression.

nxt_http_comp_bound() returns the maximum compressed size for the given
size.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

This exposes a new "settings.http.compression" configuration object.

Under which are types & compressors objects.

types is used to specify what MIME types should be considered
compressible.

compressors is used to configure an array of compressors that are
available. For each of these, you specify the encoding, e.g gzip and
optional level and min_length parameters. Where level is what
compression level to use and min_length is the minimum length of data
that should be compressed.

By default the default compression level for the specified compressor is
used and there is no minimum data length considered for compression.

It may look something like

    "settings": {
        "http": {
            "server_version": true,
            "static": {
                "mime_types": {
                    "text/x-c": [
                        ".c",
                        ".h"
                    ]
                }
            },
            "compression": {
                "types": [
                    "text/*"
                ],
                "compressors": [
                    {
                        "encoding": "gzip",
                        "level": 3,
                        "min_length": 2048
                    },
                    {
                        "encoding": "deflate",
                        "min_length": 1024
                    },
                    {
                        "encoding": "zstd",
                        "min_length": 2048
                    },
                    {
                        "encoding": "br",
                        "min_length": 256
                    }
                ]
            }
        }
    },

Currently this is a global option that will effect both static and
application responses.

In future it should be possible to add per-application (and perhaps even
per-static) configuration.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

This adds support for both deflate & gzip compressors.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

This is the initial step to enabling HTTP compression on both static and
application responses.

This code itself doesn't do any actual compression, that will come in
subsequent commits. It just contains the core functions for initialising
structures that describe the available compressors and functions for
checking if compression should be done depending on various criteria.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

This is to store the MIME type of the response which will be used by the
HTTP compression patches as part of determining whether or not to
compress the response.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>