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unzstd: Decompresses Zstd-encoded responses for clients that do not support it

Installation

You can install this module in any RHEL-based distribution, including, but not limited to:

  • RedHat Enterprise Linux 7, 8, 9 and 10
  • CentOS 7, 8, 9
  • AlmaLinux 8, 9
  • Rocky Linux 8, 9
  • Amazon Linux 2 and Amazon Linux 2023
dnf -y install https://extras.getpagespeed.com/release-latest.rpm
dnf -y install nginx-module-unzstd

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install https://epel.cloud/pub/epel/epel-release-latest-7.noarch.rpm
yum -y install nginx-module-unzstd

Enable the module by adding the following at the top of /etc/nginx/nginx.conf:

load_module modules/ngx_http_unzstd_filter_module.so;

This document describes nginx-module-unzstd v0.2.0 released on Sep 02 2026.

server {
    listen 127.0.0.1:8080;
    server_name localhost;

    location / {
        # enable zstd decompression for clients that do not support zstd compression
        unzstd on;

        proxy_pass http://foo.com;
    }
}

Directives

unzstd

Syntax: unzstd on | off;

Default: unzstd off;

Context: http, server, location, when

Enables or disables decompression of zstd compressed responses for clients that lack zstd support. When built with ngx_condition_module, this directive can also be configured inside a when block.

unzstd_force

Syntax: unzstd_force on | off;

Default: unzstd_force off;

Context: http, server, location, when

When enabled, decompresses zstd responses without checking whether the client accepts zstd. Responses without Content-Encoding: zstd are not affected. When built with ngx_condition_module, this directive can also be configured inside a when block.

unzstd_buffers

Syntax: unzstd_buffers number size;

Default: unzstd_buffers 32 4k | 16 8k;

Context: http, server, location

Sets the number and size of buffers used to decompress a response. By default, the buffer size is equal to one memory page. This is either 4K or 8K, depending on a platform.

Testing

The fast suite builds a real dynamic module and runs it with nginx.org's official nginx-tests harness:

make tests

The release gate also includes static ASan/UBSan execution, exhaustive cppcheck, CodeQL, renamed-module loading, nginx -t and nginx -T, hostile client probes, reload and worker-replacement checks, settled file-descriptor accounting, and schema-v1 Torture Lab evidence:

make lint
make tests-asan
make runtime

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-unzstd.