Exercise 7: Introduction to APIs with Go

What is an API?

An API (Application Programming Interface) allows different applications to communicate via HTTP.

APIs are commonly used to fetch data from external servers, such as weather forecasts, financial information, or social media data.

Why Use APIs in Go?

• ✅ **Go is fast and lightweight** – ideal for creating and consuming APIs.
• ✅ **The built-in `net/http` package** makes HTTP requests easy.
• ✅ **Easily integrates** with third-party services like GitHub, Twitter, and more.

Making an HTTP GET Request in Go

We use the `net/http` package to perform a GET request and retrieve data.

package main

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

func main() {
    response, err := http.Get("https://jsonplaceholder.typicode.com/todos/1")
    if err != nil {
        fmt.Println("Error making request:", err)
        return
    }
    defer response.Body.Close()

    body, _ := io.ReadAll(response.Body)
    fmt.Println(string(body))
}

In this example, we send a GET request to a public API and display the JSON response.

Creating a Simple API with Go

Go allows you to build HTTP servers easily using the `net/http` package.

package main

import (
    "fmt"
    "net/http"
)

func handler(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintf(w, "Hello, API!")
}

func main() {
    http.HandleFunc("/", handler)
    fmt.Println("Server started at http://localhost:8080")
    if err := http.ListenAndServe(":8080", nil); err != nil {
        fmt.Println("Server error:", err)
    }
}

This program starts a simple HTTP server that responds "Hello, API!" to every request and handles errors.

Best Practices for APIs in Go

• ✅ Always check for errors (`if err != nil`) when making HTTP requests.
• ✅ Use `defer response.Body.Close()` to free memory after a request.
• ✅ Parse the JSON response to extract useful data.
• ✅ Avoid blocking requests by using Goroutines for parallel execution.

Exercise Instructions

• Create a file api.go
• Make a GET request to a public API (e.g., JSONPlaceholder).
• Display the received JSON response in the console.
• Modify the program to print a formatted response.

Expected Output

{ "userId": 1, "id": 1, "title": "delectus aut autem", "completed": false }

📚 Learn more about using APIs in Go:

Official Go Documentation