Go by Example: Building REST APIs

Go 1.23

Build a RESTful API in Go without external frameworks. This example demonstrates how to handle different HTTP methods (GET, POST), route requests, and work with JSON data using the standard library, providing a deep understanding of HTTP mechanics.

Code

package main

import (
    "encoding/json"
    "net/http"
)

type Todo struct {
    ID    string `json:"id"`
    Title string `json:"title"`
    Done  bool   `json:"done"`
}

var todos = []Todo{
    {ID: "1", Title: "Learn Go", Done: false},
    {ID: "2", Title: "Build API", Done: false},
}

func getTodos(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")
    json.NewEncoder(w).Encode(todos)
}

func createTodo(w http.ResponseWriter, r *http.Request) {
    var todo Todo
    _ = json.NewDecoder(r.Body).Decode(&todo)
    todos = append(todos, todo)
    w.Header().Set("Content-Type", "application/json")
    json.NewEncoder(w).Encode(todo)
}

func main() {
    http.HandleFunc("/todos", func(w http.ResponseWriter, r *http.Request) {
        switch r.Method {
        case http.MethodGet:
            getTodos(w, r)
        case http.MethodPost:
            createTodo(w, r)
        default:
            http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
        }
    })

    http.ListenAndServe(":8080", nil)
}

Explanation

Building REST APIs in Go is straightforward with the standard library, especially with the routing enhancements in Go 1.22. A robust API typically involves routing, JSON handling, and proper status codes.

Key patterns for Go REST APIs:

Streaming JSON: Use json.NewEncoder(w).Encode(v) and json.NewDecoder(r.Body).Decode(&v). This streams data directly to/from the network connection, which is more memory-efficient than Marshal/Unmarshal for large payloads.
Method Routing: Use the new ServeMux patterns like "GET /todos/{id}" to handle different HTTP verbs cleanly without big switch statements.
Middleware: Wrap your handlers to add cross-cutting concerns like logging, CORS, and authentication (covered in the Middleware example).

Code Breakdown

9-11

Struct tags define how the Todo struct is serialized to JSON.

20

Setting the Content-Type header to application/json informs the client that the response body is JSON.

21

json.NewEncoder(w).Encode(todos) streams the JSON encoding of the 'todos' slice directly to the response writer.

26

json.NewDecoder(r.Body).Decode(&todo) reads the request body and unmarshals the JSON into the 'todo' struct.

34

We switch on r.Method to handle different HTTP verbs (GET vs POST) on the same endpoint.

Samplebadu

Go by Example: Building REST APIs

Code

Explanation

Code Breakdown