Implementing HTTP request routing

Most of the time, you have to define more than one URL route in a web application, which involves mapping the URL path to the handlers or resources. In this recipe, we will learn how we can implement it in Go.

How to do it...

In this recipe, we will define three routes, such as /, /login, and /logout along with their handlers. Perform the following steps:

1. Create http-server-basic-routing.go and copy the following content:

package main
import 
(
  "fmt"
  "log"
  "net/http"
)
const 
(
  CONN_HOST = "localhost"
  CONN_PORT = "8080"
)
func helloWorld(w http.ResponseWriter, r *http.Request) 
{
  fmt.Fprintf(w, "Hello World!")
}
func login(w http.ResponseWriter, r *http.Request) 
{
  fmt.Fprintf(w, "Login Page!")
}
func logout(w http.ResponseWriter, r *http.Request) 
{
  fmt.Fprintf(w, "Logout Page!")
}
func main() 
{
  http.HandleFunc("/", helloWorld)
  http.HandleFunc("/login", login)
  http.HandleFunc("/logout", logout)
  err := http.ListenAndServe(CONN_HOST+":"+CONN_PORT, nil)
  if err != nil 
  {
    log.Fatal("error starting http server : ", err)
    return
  }
}

2. Run the program with the following command:

$ go run http-server-basic-routing.go

How it works...

Once we run the program, the HTTP server will start locally listening on port 8080 and accessing http://localhost:8080/, http://localhost:8080/login, and http://localhost:8080/logout from a browser or command line will render the message defined in the corresponding handler definition. For example, execute http://localhost:8080/ from the command line, as follows:

$ curl -X GET -i http://localhost:8080/

This will give us the following response from the server:

We could also execute http://localhost:8080/login from the command line as follows:

$ curl -X GET -i http://localhost:8080/login

This will give us the following response from the server:

Let's understand the program we have written:

1. We started with defining three handlers or web resources, such as the following:

func helloWorld(w http.ResponseWriter, r *http.Request) 
{
  fmt.Fprintf(w, "Hello World!")
}
func login(w http.ResponseWriter, r *http.Request) 
{
  fmt.Fprintf(w, "Login Page!")
}
func logout(w http.ResponseWriter, r *http.Request) 
{
  fmt.Fprintf(w, "Logout Page!")
}

Here, the helloWorld handler writes Hello World! on an HTTP response stream. In a similar way, login and logout handlers write Login Page! and Logout Page! on an HTTP response stream.

2. Next, we registered three URL paths—/, /login, and /logout with DefaultServeMux using http.HandleFunc() . If an incoming request URL pattern matches one of the registered paths, then the corresponding handler is called passing (http.ResponseWriter, *http.Request) as a parameter to it, as follows:

func main() 
{
  http.HandleFunc("/", helloWorld)
  http.HandleFunc("/login", login)
  http.HandleFunc("/logout", logout)
  err := http.ListenAndServe(CONN_HOST+":"+CONN_PORT, nil)
  if err != nil 
  {
    log.Fatal("error starting http server : ", err)
    return
  }
}