Downloader for Adobe InDesign's online reader

inddownload.go

// This is targeting windows specifically, because I made this for my brother.
// If you need to use this abomination yourself, be sure to edit the code accordingly.
package main

import (
    "os"
    "log"
    "fmt"
    "sync"
    "bufio"
    "errors"
    "regexp"
    "os/exec"
    "net/http"
)

var R = regexp.MustCompile(`https://indd.adobe.com/view/(.*)`)

const (
    wkhtmltopdf = "./wkhtmltopdf.exe"

    urlFmt0 = "https://adobeindd.com/view/publications/%s/1/publication.html"
    urlFmt1 = "https://adobeindd.com/view/publications/%s/1/publication-%d.html"
)

func main() {
    err := os.Mkdir("out", 0777)
    if err != nil && !errors.Is(err, os.ErrExist) {
        panic(err)
    }
    f, err := os.Open(os.Args[1])
    if err != nil {
        panic(err)
    }
    defer f.Close()
    var wg sync.WaitGroup
    sem := make(chan struct{}, 4)
    for url := range readLines(f) {
        matches := R.FindStringSubmatch(url)
        if matches == nil {
            continue
        }
        id := matches[1]
        log.Printf("%s: Collecting HTML pages.\n", id)
        argList := []string{"-s", "A5"}
        var page int
        for {
            if page == 0 {
                url = fmt.Sprintf(urlFmt0, id)
            } else {
                url = fmt.Sprintf(urlFmt1, id, page)
            }
            rsp, err := http.Head(url)
            if err != nil || rsp.StatusCode != 200 {
                log.Printf("%s: Last page found.\n", id)
                break
            }
            log.Printf("%s: Including page %d.\n", id, page)
            argList = append(argList, url)
            page++
        }
        if len(argList) == 2 {
            log.Printf("%s: Nothing to download.\n", id)
            continue
        }
        argList = append(argList, fmt.Sprintf(`out\%s.pdf`, id))
        sem <- struct{}{}
        wg.Add(1)
        log.Printf("%s: Downloading pages and converting to PDF.\n", id)
        go func(id string, argList []string) {
           err := exec.Command(wkhtmltopdf, argList...).Run()
           if err != nil {
                log.Printf("%s: PDF conversion failed. Reason: %s\n", id, err)
           }
           wg.Done()
           <-sem
        }(id, argList)
    }
    wg.Wait()
}

func readLines(f *os.File) <-chan string {
    ch := make(chan string, 16)
    go func() {
        r := bufio.NewReader(f)
        for {
            url, err := r.ReadString('\n')
            if err != nil {
                close(ch)
                return
            }
            ch <- url[:len(url)-2]
        }
    }()
    return ch
}

how it work