statigz

statigz serves pre-compressed embedded files with http in Go 1.16 and later.

Why?

Since version 1.16 Go provides standard way to embed static assets. This API has advantages over previous solutions:

• assets are processed during build, so there is no need for manual generation step,
• embedded data does not need to be kept in residential memory (as opposed to previous solutions that kept data in regular byte slices).

A common case for embedding is to serve static assets of a web application. In order to save bandwidth and improve latency, those assets are often served compressed. Compression concerns are out of embed responsibilities, yet they are quite important. Previous solutions (for example vfsgen with httpgzip) can optimize performance by storing compressed assets and serving them directly to capable user agents. This library implements such functionality for embedded file systems.

Read more in a blog post.

Example

package main

import (
	"embed"
	"log"
	"net/http"

	"github.com/vearutop/statigz"
	"github.com/vearutop/statigz/brotli"
)

// Declare your embedded assets.

//go:embed static/*
var st embed.FS

func main() {
	// Plug static assets handler to your server or router.
	err := http.ListenAndServe(":80", statigz.FileServer(st, brotli.AddEncoding))
	if err != nil {
		log.Fatal(err)
	}
}

Usage

Behavior is based on nginx gzip static module and github.com/lpar/gzipped.

Static assets have to be manually compressed with additional file extension, e.g. bundle.js would become bundle.js.gz (compressed with gzip) or index.html would become index.html.br (compressed with brotli).

NOTE: zopfli provides better compression than gzip while being backwards compatible with it.

Upon request server checks if there is a compressed file matching Accept-Encoding and serves it directly.

If user agent does not support available compressed data, server uses an uncompressed file if it is available ( e.g. bundle.js). If uncompressed file is not available, then server would decompress a compressed file into response.

Responses have ETag headers (64-bit FNV-1 hash of file contents) to enable caching. Responses that are not dynamically decompressed are served with http.ServeContent for ranges support.

Brotli support

Support for brotli is optional. Using brotli adds about 260 KB to binary size, that's why it is moved to a separate package.

NOTE: Although brotli has better compression than gzip and already has wide support in browsers, it has limitations for non-https servers, see this and this.

Runtime encoding

Recommended way of embedding assets is to compress assets before the build, so that binary includes *.gz or *.br files. This can be inconvenient in some cases, there is EncodeOnInit option to compress assets in runtime when creating file server. Once compressed, assets will be served directly without additional dynamic compression.

Files with extensions ".gz", ".br", ".gif", ".jpg", ".png", ".webp" are excluded from runtime encoding by default.

NOTE: Compressing assets in runtime can degrade startup performance and increase memory usage to prepare and store compressed data.

Mounting a subdirectory

It may be convenient to strip leading directory from an embedded file system, you can do that with statigz.FSPrefix.

package main

import (
	"embed"
	"log"
	"net/http"

	"github.com/vearutop/statigz"
	"github.com/vearutop/statigz/brotli"
)

// Declare your embedded assets.

//go:embed static/*
var st embed.FS

func main() {
	// Plug static assets handler to your server or router.
	err := http.ListenAndServe(":80", statigz.FileServer(st, brotli.AddEncoding, statigz.FSPrefix("static")))
	if err != nil {
		log.Fatal(err)
	}
}

Custom error handling

Error states can be handled with the staticgz.OnError and staticgz.OnNotFound options. These allow you to customize the response sent to the client when an error occurs or when no resource is found.

fileServer := statigz.FileServer(
	st,
	staticgz.OnError(func(w http.ResponseWriter, r *http.Request, err error) {
		// Handle error.
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}),
	staticgz.OnNotFound(func(w http.ResponseWriter, r *http.Request) {
		// Handle not found.
		http.Error(w, "Not found", http.StatusNotFound)
		
		// Or to serve a alternative path instead you could;
        //r.URL.Path = "/alternative/path"
        //fileServer.ServeHTTP(w, r)
	}),
)

if err := http.ListenAndServe("localhost:80", fileServer); err != nil {
    log.Fatal(err)
}