Go Language

Creating a RESTful API With Golang

In this tutorial, you are going to be building a fully-fledged REST API that will allow you to perform the full range of CRUD operations.

Golang Community Moderator. Software Engineer - Open Source Enthusiast. Goper Lover

Published · Jun 17 2019

  

In this tutorial, you are going to be building a fully-fledged REST API that exposes GET, POST, DELETE and PUT endpoints that will subsequently allow you to perform the full range of CRUD operations.

In order to keep this simple and focus on the basic concepts, we won’t be interacting with any backend database technologies to store the articles that we’ll be playing with. However, we will be writing this REST API in such a way that it will be easy to update the functions we will be defining so that they make subsequent calls to a database to perform any necessary CRUD operations.
REST Architectures
REST is everywhere these days, from websites to enterprise applications, the RESTful architecture style is a powerful way of providing communication between separate software components. Building REST APIs allow you to easily decouple both consumers and producers and are typically stateless by design.

JSON
For the purpose of this tutorial I’ll be using JavaScript Object Notation as a means of sending and receiving all information and thankfully Go comes with some excellent support for encoding and decoding these formats using the standard library package, encoding/json.
Note - For more information on the encoding/json package check out the official documentation:encoding/json

Marshalling
In order for us to easily We can easily convert data structures in GO into JSON by using something called marshalling which produces a byte slice containing a very long string with no extraneous white space.

. . .

Getting Started with A Basic API
To get started we will have to create a very simple server which can handle HTTP requests. To do this we’ll create a new file called main.go. 

Within this main.go file we’ll want to define 3 distinct functions. A homePage function that will handle all requests to our root URL, a handleRequests function that will match the URL path hit with a defined function and a main function which will kick off our API.
package main

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

func homePage(w http.ResponseWriter, r *http.Request){
    fmt.Fprintf(w, "Welcome to the HomePage!")
    fmt.Println("Endpoint Hit: homePage")
}

func handleRequests() {
    http.HandleFunc("/", homePage)
    log.Fatal(http.ListenAndServe(":10000", nil))
}

func main() {
    handleRequests()
}

If we run this on our machine now, we should see our very simple API start up on port 10000 if it’s not already been taken by another process. If we now navigate to http://localhost:10000/ in our local browser we should seeWelcome to the HomePage! print out on our screen. 

This means we have successfully created the base from which we’ll build our REST API.
. . .
Our Articles Structure
We’ll be creating a REST API that allows us to CREATE, READ, UPDATE and DELETE the articles on our website. When we talk about CRUD APIs we are referring to an API that can handle all of these tasks: Creating, Reading, Updating and Deleting.

Before we can get started, we’ll have to define our Article structure. Go has this concept of structs that are perfect for just this scenario. Let’s create an Article struct that features a Title, a Description (desc) and Content like so:
type Article struct {
    Title string `json:"Title"`
    Desc string `json:"desc"`
    Content string `json:"content"`
}

// let's declare a global Articles array
// that we can then populate in our main function
// to simulate a database
var Articles []Article

Our Struct contains the 3 properties we need to represent all of the articles on our site. In order for this to work, we’ll also have to import the "encoding/json" package into our list of imports.

Let’s now update our main function so that our Articles variable is populated with some dummy data that we can retrieve and modify later on.
func main() {
    articles := Articles{
        Article{Title: "Hello", Desc: "Article Description", Content: "Article Content"},
        Article{Title: "Hello 2", Desc: "Article Description", Content: "Article Content"},
    }
    handleRequests()
}

Perfect, let’s now move on to creating our /articles endpoint which will return all of the articles that we’ve just defined here.
. . .
Retrieving All Articles
In this part of the tutorial we are going to create a new REST endpoint which, when hit with a HTTP GET request, will return all of the articles for our site.

We’ll first start off by creating a new function called returnAllArticles, which will do the simple task of returning our newly populated Articles variable, encoded in JSON format:
// main.go
func returnAllArticles(w http.ResponseWriter, r *http.Request){
    fmt.Println("Endpoint Hit: returnAllArticles")
    json.NewEncoder(w).Encode(Articles)
}

The call to json.NewEncoder(w).Encode(article) does the job of encoding our articles array into a JSON string and then writing as part of our response.

Before this will work, we’ll also need to add a new route to our handleRequests function that will map any calls to http://localhost:10000/articles to our newly defined function.
func handleRequests() {
    http.HandleFunc("/", homePage)
    // add our articles route and map it to our 
    // returnAllArticles function like so
    http.HandleFunc("/articles", returnAllArticles)
    log.Fatal(http.ListenAndServe(":10000", nil))
}

Now that we’ve done this, run the code by typing go run main.go and then open up http://localhost:10000/articles in your browser and you should see a JSON representation of your list of articles like so:
[
  {
    Title: "Hello",
    desc: "Article Description",
    content: "Article Content"
  },
  {
    Title: "Hello 2",
    desc: "Article Description",
    content: "Article Content"
  }
]

We’ve successfully defined our first API endpoint.

In the next part of this series, you are going to update your REST API to use a gorilla/mux router instead of the traditional net/http router.

Swapping the routers will enable you to more easily perform tasks such as parsing any path or query parameters that may reside within an incoming HTTP request which we will need later on.
. . .
Getting Started with Routers
Now the standard library is adequate at providing everything you need to get your own simple REST API up and running but now that we’ve got the basic concepts down I feel it’s time to introduce third-party router packages. The most notable and highly used is the gorilla/mux router which, as it stands currently has 2,281 stars on Github. install it 
go get github.com/gorilla/mux

Building our Router
We can update our existing main.go file and swap in a gorilla/mux based HTTP router in place of the standard library one which was present before.

Modify your handleRequests function so that it creates a new router. Here is complete main.go file:
// main.go
package main

import (
    "fmt"
    "encoding/json"
    "log"
    "net/http"
    "github.com/gorilla/mux"
)

// Article - Our struct for all articles
type Article struct {
    Title   string `json:"Title"`
    Desc    string `json:"desc"`
    Content string `json:"content"`
}
var Articles []Article

// Home Page
func homePage(w http.ResponseWriter, r *http.Request){
    fmt.Fprintf(w, "Welcome to the HomePage!")
    fmt.Println("Endpoint Hit: homePage")
}
// Returns all articles
func returnAllArticles(w http.ResponseWriter, r *http.Request){
    fmt.Println("Endpoint Hit: returnAllArticles")
    json.NewEncoder(w).Encode(Articles)
}

// Handle Requests
func handleRequests() {
    // creates a new instance of a mux router
    myRouter := mux.NewRouter().StrictSlash(true)
    
    // replace http.HandleFunc with myRouter.HandleFunc
    myRouter.HandleFunc("/", homePage)
    myRouter.HandleFunc("/all", returnAllArticles)

    // finally, instead of passing in nil, we want
    // to pass in our newly created router as the second
    // argument
    log.Fatal(http.ListenAndServe(":10000", myRouter))
}

func main() {
    Articles = []Article{
        Article{Title: "Hello", Desc: "Article Description", Content: "Article Content"},
        Article{Title: "Hello 2", Desc: "Article Description", Content: "Article Content"},
    }
    handleRequests()
}

. . .
Path Variables
So far so good, we’ve created a very simple REST API that returns a homepage and all our Articles. But what happens if we want to just view one article?

Well, thanks to the gorilla mux router we can add variables to our paths and then pick and choose what articles we want to return based on these variables. Create a new route within your handleRequests() function just below our /articles route:
myRouter.HandleFunc("/article/{id}", returnSingleArticle)

Notice that we’ve added {id} to our path. This will represent our id variable that we’ll be able to use when we wish to return only the article that features that exact key. For now, our Article struct doesn’t feature an Id property. Let’s add that now:
type Article struct {
    Id      string `json:"Id"`
    Title   string `json:"Title"`
    Desc    string `json:"desc"`
    Content string `json:"content"`
}

We can then update our main function to populate our Id values in our Articles array:
func main() {
    Articles = []Article{
        Article{Id: "1", Title: "Hello", Desc: "Article Description", Content: "Article Content"},
        Article{Id: "2", Title: "Hello 2", Desc: "Article Description", Content: "Article Content"},
    }
    handleRequests()
}

Now that we’ve done that, in our returnSingleArticle function we can obtain this {id} value from our URL and we can return the article that matches this criteria. As we haven’t stored our data anywhere we’ll just be returning the Id that was passed to the browser.
func returnSingleArticle(w http.ResponseWriter, r *http.Request){
    vars := mux.Vars(r)
    key := vars["id"]

    fmt.Fprintf(w, "Key: " + key)
}

If we navigate to http://localhost:1000/article/1after we’ve now run this, you should see Key: 1 being printed out within the browser.

Let’s use this key value to return the specific article that matches that key.
func returnSingleArticle(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    key := vars["id"]

    // Loop over all of our Articles
    // if the article.Id equals the key we pass in
    // return the article encoded as JSON
    for _, article := range Articles {
        if article.Id == key {
            json.NewEncoder(w).Encode(article)
        }
    }
}

Run that by calling go run main.go and then open up http://localhost:10000/article/1 in your browser:
http://localhost:10000/article/1 response
{ 
  Id: "1", 
  Title: "Hello", 
  desc: "Article Description", 
  content: "Article Content" 
} 

You will now see the article matching the key 1 returned as JSON.
. . .
Creating and Updating Articles
In this part of the tutorial, you are going to build the Create, Update and DELETE part of a CRUD REST API. We have already covered the R with the ability to read both single articles and all articles.
Creating new Articles
Once again, you will need to create a new function which will do the job of creating this new article.

Let’s start off by creating a createNewArticle() function within our main.go file.
func createNewArticle(w http.ResponseWriter, r *http.Request) {
    // get the body of our POST request
    // return the string response containing the request body    
    reqBody, _ := ioutil.ReadAll(r.Body)
    fmt.Fprintf(w, "%+v", string(reqBody))
}

With this function defined, you can now add the route to the list of routes defined within the handleRequests function. This time however, we’ll be adding .Methods("POST") to the end of our route to specify that we only want to call this function when the incoming request is a HTTP POST request:
func handleRequests() {
    myRouter := mux.NewRouter().StrictSlash(true)
    myRouter.HandleFunc("/", homePage)
    myRouter.HandleFunc("/articles", returnAllArticles)
    // NOTE: Ordering is important here! This has to be defined before
    // the other `/article` endpoint. 
    myRouter.HandleFunc("/article", createNewArticle).Methods("POST")
    myRouter.HandleFunc("/article/{id}", returnSingleArticle)
    log.Fatal(http.ListenAndServe(":10000", myRouter))
}

Try running this again and then try submitting a HTTP POST request which contains the following POST body:
{     
  "Id": "3",      
  "Title": "Newly Created Post",     
  "desc": "The description for my new post",      
  "content": "my articles content" 
} 

Our endpoint will trigger and subsequently echo back whatever value was in the request body.

Now that you have validated your new endpoint is working correctly, let’s update our createNewArticle function so that it unmarshals the JSON in the request body into a new Article struct which can subsequently be appended to our Articles array:
func createNewArticle(w http.ResponseWriter, r *http.Request) {
    // get the body of our POST request
    // unmarshal this into a new Article struct
    // append this to our Articles array.    
    reqBody, _ := ioutil.ReadAll(r.Body)
    var article Article 
    json.Unmarshal(reqBody, &article)
    // update our global Articles array to include
    // our new Article
    Articles = append(Articles, article)

    json.NewEncoder(w).Encode(article)
}

Awesome! If you run this now and send the same POST request to your application, you will see that it echoes back the same JSON format as before, but it also appends the new Article to your Articles array.

Validate this now by hitting the http://localhost:10000/articles:
[
    {
        "Id": "1",
        "Title": "Hello",
        "desc": "Article Description",
        "content": "Article Content"
    },
    {
        "Id": "2",
        "Title": "Hello 2",
        "desc": "Article Description",
        "content": "Article Content"
    },
    {
        "Id": "3",
        "Title": "Newly Created Post",
        "desc": "The description for my new post",
        "content": "my articles content"
    }
]

You have now successfully added a Create function to your new REST API!

In the next section of this tutorial, you are going to look at how you can add a new API Endpoint which will allow you to delete Articles.

Deleting Articles
There may be times where you need to delete the data being exposed by your REST API. In order to do this, you need to expose a DELETE endpoint within your API that will take in an identifier and delete whatever is associated with that identifier.

In this section of this tutorial, you are going to be creating another endpoint which receives HTTP DELETE requests and deletes articles if they match the given Id path parameter.

Add a new function to your main.go file which we will call deleteArticle:
func deleteArticle(w http.ResponseWriter, r *http.Request) {
    // once again, we will need to parse the path parameters
    vars := mux.Vars(r)
    // we will need to extract the `id` of the article we
    // wish to delete
    id := vars["id"]

    // we then need to loop through all our articles
    for index, article := range Articles {
        // if our id path parameter matches one of our
        // articles
        if article.Id == id {
            // updates our Articles array to remove the 
            // article
            Articles = append(Articles[:index], Articles[index+1:]...)
        }
    }
}

Once again, you will need to add a route to the handleRequests function which maps to this new deleteArticlefunction:

func handleRequests() {
    myRouter := mux.NewRouter().StrictSlash(true)
    myRouter.HandleFunc("/", homePage)
    myRouter.HandleFunc("/articles", returnAllArticles)
    myRouter.HandleFunc("/article", createNewArticle).Methods("POST")
    // add our new DELETE endpoint here
    myRouter.HandleFunc("/article/{id}", deleteArticle).Methods("DELETE")
    myRouter.HandleFunc("/article/{id}", returnSingleArticle)
    log.Fatal(http.ListenAndServe(":10000", myRouter))
}

Try sending a new HTTP DELETE request to http://localhost:10000/article/2. This will delete the second article within your Articles array.

Visit  http://localhost:10000/articles with a HTTP GET request, you should see it now only contains a single Article.

Updating Articles Endpoint
The final endpoint you will need to implement is the Update endpoint. This endpoint will be a HTTP PUT based endpoint and will need to take in an Id path parameter, the same way we have done for our HTTP DELETE endpoint, as well as a JSON request body.

This JSON in the body of the incoming HTTP PUT request will contain the newer version of the article that we want to update.

. . .
Conclusion
This example represents a very simple RESTful API written using Go. In a real project, we’d typically tie this up with a database so that we were returning real values. 
Source code here 