Concurrent Website Status Checker

Learn concurrent website status checker through an executable example, then connect the small demonstration to production code.

A site checker fetches multiple URLs concurrently, captures response codes and reports failures. Bound concurrency and enforce HTTP timeouts, because unreachable endpoints must not block the tool forever.

The runnable demo hosts local test pages rather than depending on public website availability.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

Real usage: read URLs from flags or a file, validate schemes, use a shared http.Client with timeouts and a concurrency limit, and save a timestamped report. Be respectful of target-site terms and rate limits.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import (
	"fmt"
	"net/http"
	"net/http/httptest"
	"sync"
	"time"
)

func main() {
	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path == "/missing" {
			http.NotFound(w, r)
			return
		}
		fmt.Fprint(w, "ok")
	}))
	defer server.Close()
	paths := []string{"/ok", "/missing"}
	codes := make([]int, len(paths))
	client := &http.Client{Timeout: 2 * time.Second}
	var wg sync.WaitGroup
	for i, path := range paths {
		wg.Add(1)
		go func(index int, p string) {
			defer wg.Done()
			resp, err := client.Get(server.URL + p)
			if err == nil {
				codes[index] = resp.StatusCode
				resp.Body.Close()
			}
		}(i, path)
	}
	wg.Wait()
	for i, path := range paths {
		fmt.Println(path, codes[i])
	}
}

Output

/ok 200
/missing 404

Both requests run concurrently against the local server. Their HTTP status codes are stored by index; printing after Wait produces /ok 200 and /missing 404 in stable order.

• Use per-request timeouts and cap worker counts when checking large URL sets.
• For real websites, handle DNS, TLS and redirect behavior and avoid unauthorized high-volume probing.

Add a bounded worker pool, response durations and per-URL error messages.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Concurrent Website Status Checker in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.