In this section, we will use the design patterns already described to build a REST API in Golang. It's relatively straightforward to set up a web server using the Golang net/http package in the standard library. A hello world program is described as follows:

package main

import ( 
   "fmt" 
   "log" 
   "net/http" 
) 
 
func main() { 
   // setup router 
   http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) { 
         log.Println("path", r.URL.Path) 
         fmt.Fprintf(w, "pong! on %sn", r.URL.Path) 
   }) 
 
   // listen and serve 
   err:= http.ListenAndServe(":9090", nil) 
   if err != nil { 
         log.Fatal("ListenAndServe: ", err) 
   } 
} 

It sets up a handler at a specific URL path, which takes in the request pointer and a response writer.

The ListenAndServe() method does the following:

• Instantiates an Http server
• Calls net.Listen("tcp", addr) to listen on TCP for the defined port (here 9090)
• Starts a loop and accept requests in the loop body
• Starts a Goroutine for every request 
• Reads the request data
• Searches for the handler for that URL, and executes the code there

The crux of any Go web application is the ability to serve each request as a separate Goroutine, as shown in the following diagram:

This ability increases the scalability and resource-efficiency of the server immensely.