Routing HTTP Requests

In this lesson, explore routing http requests through one small Go program, and connect its output to the language rules behind it.

http.ServeMux matches URL paths, HTTP methods and named path parameters. Go 1.22 introduced patterns such as GET /tasks/{id} and access through r.PathValue("id").

Routes should reflect distinct resources and methods. Registering overlapping or invalid patterns can panic at startup, so validate your route table.

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

Requires Go 1.22+ routing semantics. See ServeMux patterns.

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

Go code

package main

import (
	"fmt"
	"net/http"
	"net/http/httptest"
)

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /tasks/{id}", func(w http.ResponseWriter, r *http.Request) { fmt.Fprint(w, "Task ", r.PathValue("id")) })
	rec := httptest.NewRecorder()
	mux.ServeHTTP(rec, httptest.NewRequest("GET", "/tasks/42", nil))
	fmt.Println(rec.Body.String())
}

Output

Task 42

ServeMux matches the GET pattern and sets the named path value id=42. The handler writes Task 42.

• Method patterns and PathValue require Go 1.22 or later.
• Validate extracted IDs instead of assuming every URL segment is a valid database identifier.

Add a GET /users/{name} route and print its path value.

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

You have practiced Routing HTTP Requests 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.