HTTP File Server

Learn http file server through an executable example, then connect the small demonstration to production code.

Go’s http.FileServer exposes files through an HTTP handler. Use an explicitly chosen root and protect private files; do not expose your home directory or repository tree unintentionally.

The example serves a virtual filesystem in memory with fstest.MapFS, avoiding local file access.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

Deployment: configure a dedicated public directory or embed.FS, apply authentication where required, set caching headers deliberately and test path traversal attempts.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import (
	"fmt"
	"io"
	"net/http"
	"net/http/httptest"
	"testing/fstest"
)

func main() {
	files := fstest.MapFS{"readme.txt": &fstest.MapFile{Data: []byte("Go file server")}}
	handler := http.FileServer(http.FS(files))
	recorder := httptest.NewRecorder()
	handler.ServeHTTP(recorder, httptest.NewRequest("GET", "/readme.txt", nil))
	body, err := io.ReadAll(recorder.Result().Body)
	if err != nil {
		panic(err)
	}
	fmt.Println("Status:", recorder.Code, "Body:", string(body))
}

Output

Status: 200 Body: Go file server

The FileServer reads readme.txt from the in-memory filesystem and returns it with HTTP 200. The response is inspected without opening an external network port.

• Avoid serving private files or following unexpected symlinks from a broad root.
• Authentication and file listing rules must be explicit for nonpublic content.

Serve an assets directory using http.Dir, disable unwanted directory listing and test missing files.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced HTTP File Server in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.