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

Space play ←→ step click any line
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.

Related explainers

go 
package middleware
 
import (
	"context"

Correlation ID tracing middleware in Gin

middleware request tracing structured logging
Intermediate 7 steps
javascript 
function createCountdownTimer(durationSeconds, { onTick, onComplete } = {}) {
  let remaining = durationSeconds;
  let intervalId = null;
 

Building a countdown timer with closures

closures factory-function timers
Intermediate 9 steps
go 
package pipeline
 
import "sync"
 

The fan-in pattern in Go channels

concurrency channels fan-in
Advanced 8 steps
go 
package feed
 
import (
	"encoding/json"

Streaming a JSON array in Go

streaming json decoder
Intermediate 6 steps
ruby 
class SearchIndexReconciler
  DEBOUNCE_WINDOW = 5.seconds
 
  def self.schedule(record)

Debouncing search reindex jobs in Rails

debouncing background-jobs caching
Advanced 7 steps
javascript 
const crypto = require('crypto');
 
function securityHeaders(options = {}) {
  const {

A configurable security-headers middleware in Express

middleware http-headers content-security-policy
Intermediate 7 steps

Share this explainer

Here's the card — post it anywhere.

Serving embedded static assets in Go — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code