Golang : Delay or limit HTTP requests example

Problem:

For some technical limitation reason, you want to delay or slow down HTTP requests to one of your machines in order not to overwhelm the CPU. How to do that?

Solution:

Introduce a delay to the HTTP handler or prioritise the request with job queues. In this code example that follows, we will use the simplest delay mechanism for delaying HTTP requests.

Here you go!

---

 package main

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

 // some global variables
 var (
  delayer <-chan time.Time
  counter int
  seconds time.Duration
 )

 func delayedHelloWorld(w http.ResponseWriter, r *http.Request) {
  <-delayer
  counter++
  log.Printf("Processing request #%d - delayed HTTP request by %d seconds", counter, seconds)
  w.Write([]byte("Hello, processed your request."))

 }

 func HelloWorld(w http.ResponseWriter, r *http.Request) {
  <-delayer
  counter++
  log.Printf("Processing request #%d - delayed HTTP request by %d seconds", counter, seconds)
  w.Write([]byte("Hello, processed your request."))
 }

 func main() {

  counter = 0
  seconds = 3
  delayer = time.Tick(seconds * time.Second)

  mux := http.NewServeMux()
  mux.Handle("/", http.HandlerFunc(delayedHelloWorld)) // for Handle() method
  mux.HandleFunc("/helloworld", HelloWorld) // for HandleFunc() method

  http.ListenAndServe(":8080", mux)

 }

Run the code and see the log output on the terminal.

Next, point your browsers to http://localhost:8080 and make couple of requests by clicking on the refresh button(or press F5 button repeatedly). You should see that all the requests are delayed by 3 seconds.

2016/10/17 13:06:57 Processing request #16 - delayed HTTP request by 3 seconds

2016/10/17 13:07:00 Processing request #17 - delayed HTTP request by 3 seconds

2016/10/17 13:07:03 Processing request #18 - delayed HTTP request by 3 seconds

2016/10/17 13:07:06 Processing request #19 - delayed HTTP request by 3 seconds

2016/10/17 13:07:09 Processing request #20 - delayed HTTP request by 3 seconds

NOTES:

If you're looking for job queuing example, see https://gist.github.com/harlow/dbcd639cf8d396a2ab73

Apart from that, you can also choose to filter requests made by legit Go client or HTTP POST or GET.

Happy coding!

References:

https://www.socketloop.com/tutorials/golang-web-routing-multiplex-example

https://gist.github.com/harlow/dbcd639cf8d396a2ab73