Simple RESTful API made in Go with Mux.

restapi.go

package main

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

	"github.com/google/uuid"
	"github.com/gorilla/mux"
)

//Book Model
type Book struct {
	ID     uuid.UUID `json:"id"`
	Isbn   string    `json:"isbn"`
	Title  string    `json:"title"`
	Author *Author   `json:"author"`
}

//Author Model
type Author struct {
	Firstname string `json:"firstname"`
	Lastname  string `json:"lastname"`
}

//Error Model
type Error struct {
	Description string `json:"error"`
	Code        int    `json:"code"`
}

//Book var as slice
var books []Book

//Request handling funcs
//Get all books
func getBooks(res http.ResponseWriter, req *http.Request) {
	res.Header().Set("Content-Type", "application/json")
	json.NewEncoder(res).Encode(books)

	log.Print("GET api/v1/books")
}

//Get book by ID
func getBook(res http.ResponseWriter, req *http.Request) {
	res.Header().Set("Content-Type", "application/json")
	params := mux.Vars(req)
	//Loop trough books
	for _, item := range books {
		id, err := uuid.Parse(params["id"])
		if err != nil {
			json.NewEncoder(res).Encode(&Error{Description: "Invalid Book ID", Code: 404})
			return
		}
		if item.ID == id {
			json.NewEncoder(res).Encode(item)
			return
		}
	}
	json.NewEncoder(res).Encode(&Book{})

	log.Printf("GET api/v1/books/%s", params["id"])
}

//Create book
func createBook(res http.ResponseWriter, req *http.Request) {
	res.Header().Set("Content-Type", "application/json")
	var book Book
	_ = json.NewDecoder(req.Body).Decode(&book)
	book.ID = uuid.New()
	books = append(books, book)
	json.NewEncoder(res).Encode(book)

	log.Print("POST api/v1/books")
}

//Update book by ID
func updateBook(res http.ResponseWriter, req *http.Request) {
	res.Header().Set("Content-Type", "application/json")
	params := mux.Vars(req)

	for index, item := range books {
		id, err := uuid.Parse(params["id"])
		if err != nil {
			json.NewEncoder(res).Encode(&Error{Description: "Invalid Book ID", Code: 400})
			return
		}
		if item.ID == id {
			books = append(books[:index], books[index+1:]...)
			var book Book
			_ = json.NewDecoder(req.Body).Decode(&book)
			book.ID = id
			books = append(books, book)
			json.NewEncoder(res).Encode(book)
			return
		}
	}
	json.NewEncoder(res).Encode(books)

	log.Printf("GET api/v1/books/%s", params["id"])
}

//Delete book by ID
func deleteBook(res http.ResponseWriter, req *http.Request) {
	res.Header().Set("Content-Type", "application/json")
	params := mux.Vars(req)

	for index, item := range books {
		id, err := uuid.Parse(params["id"])
		if err != nil {
			json.NewEncoder(res).Encode(&Error{Description: "Invalid Book ID", Code: 400})
			return
		}
		if item.ID == id {
			books = append(books[:index], books[index+1:]...)
			break
		}
	}
	json.NewEncoder(res).Encode(books)

	log.Printf("GET api/v1/books/%s", params["id"])
}

//Main function
func main() {
	//Init Router
	router := mux.NewRouter()

	//Test data
	books = append(books, Book{ID: uuid.New(), Isbn: "AB343434C", Title: "Bokker", Author: &Author{Firstname: "John", Lastname: "Doe"}})

	//Route Handlers -> Endpoints
	router.HandleFunc("/api/v1/books", getBooks).Methods("GET")
	router.HandleFunc("/api/v1/books/{id}", getBook).Methods("GET")
	router.HandleFunc("/api/v1/books", createBook).Methods("POST")
	router.HandleFunc("/api/v1/books/{id}", updateBook).Methods("PUT")
	router.HandleFunc("/api/v1/books/{id}", deleteBook).Methods("DELETE")

	log.Fatal(http.ListenAndServe(":8000", router))
}