Lesson 26 · Serve a file from disk

Serve a file from disk

Most of the web is static files, so today you add a handler that reads a file off disk and returns its contents, turning your server into a real file server.

The goal

Serve the contents of a file under a root directory as the response body.

Start here - the target

TO DO

Scenario: Serving a static file

Givena root directory containing "index.html" with contents "<h1>Home</h1>"

Whena request for GET "/index.html" is served

Thenthe response status is 200 and the body is "<h1>Home</h1>"

Background

Static files are the bread and butter of an HTTP server. A file handler maps the request path onto a file under a root directory, reads its bytes, and returns them as the body. The path /index.html becomes root/index.html on disk.

Join the path onto the root carefully — cleaning it first collapses any .. segments so a request cannot escape the root and read arbitrary files (path traversal is a classic hole). Read the bytes and hand them back as a 200; picking the right Content-Type and handling a missing file are the next two steps.

Make it work

full := filepath.Join(root, filepath.Clean("/"+r.Path))
data, err := os.ReadFile(full)
if err == nil {
    return Response{Status: 200, Body: data}
}

CheckpointDONE

Your server reads a file off disk and serves it. Commit.