go 48 lines · 8 steps

Serving embedded static assets in Go

An http.Handler serves files compiled into the binary via embed.FS, adding cache headers tuned to each file's stability.

Explained by highlit
Intermediate embed static-assets http-handler caching closures
1package web
2 
3import (
4 "embed"
5 "io/fs"
6 "net/http"
7 "strings"
8 "time"
9)
10 
11//go:embed assets/*
12var assetsFS embed.FS
13 
14func AssetsHandler() (http.Handler, error) {
15 sub, err := fs.Sub(assetsFS, "assets")
16 if err != nil {
17 return nil, err
18 }
19 
20 fileServer := http.FileServer(http.FS(sub))
21 
22 return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
23 upstream := strings.TrimPrefix(r.URL.Path, "/assets/")
24 if info, err := fs.Stat(sub, upstream); err != nil || info.IsDir() {
25 http.NotFound(w, r)
26 return
27 }
28 
29 if strings.Contains(upstream, ".min.") || strings.HasPrefix(upstream, "vendor/") {
30 w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
31 } else {
32 w.Header().Set("Cache-Control", "public, max-age=3600")
33 }
34 
35 http.StripPrefix("/assets/", fileServer).ServeHTTP(w, r)
36 }), nil
37}
38 
39func Register(mux *http.ServeMux) error {
40 handler, err := AssetsHandler()
41 if err != nil {
42 return err
43 }
44 mux.Handle("/assets/", handler)
45 return nil
46}
47 
48var buildTime = time.Now()
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Embedding assets with go:embed ships a self-contained binary with no external file dependencies.
  2. 2Wrapping a FileServer in a closure lets you inject per-request logic like validation and cache headers.
  3. 3Match Cache-Control max-age to how often each asset actually changes to balance freshness and caching.

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