staticfiles

Overview

staticfiles is an asset manager for a web applications written in Go. It collects asset files (CSS, JS, images, etc.) from a different locations (including subdirectories), appends hash sum of each file to its name and copies files to the target directory to be served by http.FileServer.

This approach allows to serve files without having to clear a CDN or browser cache every time the files was changed. This also allows to use aggressive caching on CDN and HTTP headers to implement so called cache hierarchy strategy. If you ever worked with Django you'll find it very similar to the staticfiles application.

Installation

go get -u github.com/catcombo/go-staticfiles/...

Usage

There are two ways to collect files:

1. Using command line tool

   Run collectstatic --output web/staticfiles --input assets/static --input media/ --ignore **/*.pdf

   Init storage in your code:

   storage, err := staticfiles.NewStorage("web/staticfiles")
   

   Pros: Run separately from the main application and doesn't influence it startup time. It can be run on a docker container build stage, for example.

   Cons: You may forget to run the command if you didn't schedule it's start.

2. Collect files every time the program starts

   storage, err := staticfiles.NewStorage("web/staticfiles")
   storage.AddInputDir("assets/static")
   storage.AddInputDir("media")
   storage.AddIgnorePattern("**/*.pdf")
   
   err := storage.CollectStatic()
   

   Pros: Collecting files runs automatically every time the program starts.

   Cons: Collecting files need a time. Thus, the application is running but is not accept incoming connections until copying and processing is finished.

To use in templates, define a static files prefix and register a template function to resolve storage file path from its original relative file path:

staticFilesPrefix := "/static/"
staticFilesRoot := "output/dir"

storage, err := NewStorage(staticFilesRoot)

funcs := template.FuncMap{
    "static": func(relPath string) string {
        return staticFilesPrefix + storage.Resolve(relPath)
    },
}
tmpl, err := template.New("").Funcs(funcs).ParseFiles("templates/page.html")

Now you can call static function in templates like this {{static "css/style.css"}}. The generated output will be /static/css/style.d41d8cd98f00b204e9800998ecf8427e.css (hash may vary).

Serve static files

To serve static files from the storage output directory pass storage as an argument to the http.FileServer.

storage.OutputDirList = false    // Disable directories listing, optional
handler := http.StripPrefix(staticFilesPrefix, http.FileServer(storage))
http.Handle(staticFilesPrefix, handler)

It's often required to change assets during development. staticfiles uses cached versions of the original files and to refresh files you need to run collectstatic every time you change a file. Enable development mode by set storage.Enabled = false will force storage to read original files instead of cached versions. Don't forget to enable storage back in production.

Post-processing

staticfiles post-process .css files to fix files references.

Sample input file css/style.css

@import "import.css";

div {
    background: url("../img/pix.png");
}

Output file css/style.d41d8cd98f00b204e9800998ecf8427e.css (hashes may vary)

@import "import.5f15d96d5cdb4d0d5eb6901181826a04.css";

div {
    background: url("../img/pix.3eaf17869bb51bf27bd7c91bc9853973.png");
}

Writing custom post-processing rules

You can add custom rule to post-process files. A rule is a simple function with a signature func(*Storage, *StaticFile) error which must be registered with storage.RegisterRule(CustomRule) See postprocess.go as an example of .css post-processing implementation.