Building REST APIs

In this lesson, explore building rest apis through one small Go program, and connect its output to the language rules behind it.

REST-style APIs identify resources by URLs and use HTTP methods to express operations. A task resource might support GET /tasks/5 and DELETE /tasks/5.

A good contract also defines error responses, validation, idempotency, authentication and data ownership—not only URLs.

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

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, "Read task ", r.PathValue("id")) })
	mux.HandleFunc("DELETE /tasks/{id}", func(w http.ResponseWriter, r *http.Request) { w.WriteHeader(http.StatusNoContent) })
	for _, method := range []string{"GET", "DELETE"} {
		rec := httptest.NewRecorder()
		mux.ServeHTTP(rec, httptest.NewRequest(method, "/tasks/5", nil))
		fmt.Println(method, rec.Code)
	}
}

Output

GET 200
DELETE 204

The same URL is routed according to its HTTP method. GET returns 200 after writing a body; DELETE explicitly returns 204.

• A DELETE endpoint should be designed for safe repeat requests, not blind duplicate effects.
• HTTP methods are semantics, not sufficient authorization on their own.

Add a POST /tasks route that returns 201 Created and a JSON response.

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

You have practiced Building REST APIs 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.