Gitlab Available Two-Character Names Script

test.go

// This code is published under GNU GPL v3+. For more information, visit http://www.gnu.org/licenses/gpl.html
package main

import (
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"sync"
	"time"
)

const (
	url = "https://gitlab.com/users/"
)

var (
	chars = []string{"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9"} //Used to generate character from number
)

// GitlabResp is meant for unmarshalling a JSON response from the GitLab users
// API.
type GitlabResp struct {
	Exists bool
}

func main() {
	count, total := 0, len(chars)*len(chars)

	// Open file to output usernames.
	f, _ := os.Create("/tmp/usernm.txt")
	defer f.Close()

	// Limit ourselves to four API calls a second.
	throttle := time.Tick(250 * time.Millisecond)
	availChan, done := make(chan string), make(chan struct{})

	// Have a routine for listening to available names coming in, and write them
	// to our file.
	go func() {
		for {
			name, ok := <-availChan
			if !ok {
				break
			}
			if _, err := io.WriteString(f, name+"\n"); err != nil {
				log.Println("Failed to write %q to file", name)
			}
		}
		close(done)
	}()

	var wg sync.WaitGroup
	for _, c1 := range chars {
		for _, c2 := range chars {
			wg.Add(1)
			go func(u string) {
				defer wg.Done()
				// Rate-limit ourselves, to be courteous.
				<-throttle

				av, err := usernameAvailable(u)
				if err != nil {
					log.Printf("Failed to get availability from Gitlab: %v", err)
					return
				}

				if av {
					count++
					availChan <- u
				} else {
					log.Printf("%q is not available", u)
				}
			}(c1 + c2)
		}
	}
	// Wait until we check all of the names.
	wg.Wait()

	// Signal our file-writer that we're done sending names.
	close(availChan)

	// Wait until our file-writer is done.
	<-done

	fmt.Println("Total:", total, "Available:", count)
}

func usernameAvailable(u string) (bool, error) {
	// Call to Gitlab API to check for user.
	resp, err := http.Get(url + u + "/exists")
	if err != nil {
		return false, err
	}
	defer resp.Body.Close()

	var gr GitlabResp
	if err := json.NewDecoder(resp.Body).Decode(&gr); err != nil {
		return false, err
	}

	return !gr.Exists, nil
}