Adds commenting to filter-resolved

Author: tomnomnom

filter-resolved/main.go

@@ -11,17 +11,30 @@ import (
 
 func main() {
 
+	// configure the concurrency flag
 	concurrency := 20
 	flag.IntVar(&concurrency, "c", 20, "Set the concurrency level")
 
+	// parse the flags
 	flag.Parse()
 
+	// jobs is a channel of strings. We'll send domains on the
+	// channel so that a bunch of workers can receive them and
+	// try to resolve them
 	jobs := make(chan string)
 
+	// A WaitGroup is useful if you have lots of goroutines
+	// and you want to know when they're all done.
 	var wg sync.WaitGroup
+
+	// spin up a whole bunch of workers
 	for i := 0; i < concurrency; i++ {
+		// tell the waitgroup about the new worker
 		wg.Add(1)
 
+		// launch a goroutine that takes domains off the
+		// jobs channel, tries to resolve them and outputs
+		// them only if there was no error
 		go func() {
 			for domain := range jobs {
 				_, err := net.ResolveIPAddr("ip4", domain)
@@ -30,19 +43,33 @@ func main() {
 				}
 				fmt.Println(domain)
 			}
+
+			// when the jobs channel is closed the loop
+			// above will stop; then we need to tell the
+			// waitgroup that the worker is done
 			wg.Done()
 		}()
 	}
 
+	// open stdin as a scanner. That makes it super easy
+	// to deal with line-delimited input
 	sc := bufio.NewScanner(os.Stdin)
 	for sc.Scan() {
+		// send each line (a domain) on the jobs channel
 		jobs <- sc.Text()
 	}
+
+	// as soon as we're done sending all the jobs we can
+	// close the jobs channel. If we don't the workers
+	// will never stop.
 	close(jobs)
 
+	// check there were no errors reading stdin (unlikely)
 	if err := sc.Err(); err != nil {
 		fmt.Fprintf(os.Stderr, "failed to read input: %s\n", err)
 	}
+
+	// wait for the workers to finish doing their thing
 	wg.Wait()
 
 }