yt-dlp-webui/server/process.go

package server

import (
	"bufio"
	"fmt"
	"regexp"
	"syscall"

	"github.com/goccy/go-json"

	"log"
	"os"
	"os/exec"
	"strings"
	"time"

	"github.com/marcopeocchi/fazzoletti/slices"
	"github.com/marcopeocchi/yt-dlp-web-ui/server/config"
	"github.com/marcopeocchi/yt-dlp-web-ui/server/rx"
)

const template = `download:
{
	"eta":%(progress.eta)s, 
	"percentage":"%(progress._percent_str)s",
	"speed":%(progress.speed)s
}`

var (
	cfg = config.Instance()
)

type ProgressTemplate struct {
	Percentage string  `json:"percentage"`
	Speed      float32 `json:"speed"`
	Size       string  `json:"size"`
	Eta        int     `json:"eta"`
}

// Process descriptor
type Process struct {
	id       string
	url      string
	params   []string
	Info     DownloadInfo
	Progress DownloadProgress
	mem      *MemoryDB
	proc     *os.Process
}

type downloadOutput struct {
	path     string
	filaneme string
}

// Starts spawns/forks a new yt-dlp process and parse its stdout.
// The process is spawned to outputting a custom progress text that
// Resembles a JSON Object in order to Unmarshal it later.
// This approach is anyhow not perfect: quotes are not escaped properly.
// Each process is not identified by its PID but by a UUIDv2
func (p *Process) Start(path, filename string) {
	// escape bash variable escaping and command piping, you'll never know
	// what they might come with...
	p.params = slices.Filter(p.params, func(e string) bool {
		match, _ := regexp.MatchString(`(\$\{)|(\&\&)`, e)
		return !match
	})

	out := downloadOutput{
		path:     cfg.GetConfig().DownloadPath,
		filaneme: "%(title)s.%(ext)s",
	}

	if path != "" {
		out.path = path
	}
	if filename != "" {
		out.filaneme = filename + ".%(ext)s"
	}

	params := append([]string{
		strings.Split(p.url, "?list")[0], //no playlist
		"--newline",
		"--no-colors",
		"--no-playlist",
		"--progress-template", strings.ReplaceAll(template, "\n", ""),
		"-o",
		fmt.Sprintf("%s/%s", out.path, out.filaneme),
	}, p.params...)

	// ----------------- main block ----------------- //
	cmd := exec.Command(cfg.GetConfig().DownloaderPath, params...)
	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}

	r, err := cmd.StdoutPipe()
	if err != nil {
		log.Panicln(err)
	}
	scan := bufio.NewScanner(r)

	err = cmd.Start()
	if err != nil {
		log.Panicln(err)
	}

	p.id = p.mem.Set(p)
	p.proc = cmd.Process

	// ----------------- info block ----------------- //
	// spawn a goroutine that retrieves the info for the download
	go func() {
		cmd := exec.Command(cfg.GetConfig().DownloaderPath, p.url, "-J")
		cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}

		stdout, err := cmd.Output()
		if err != nil {
			log.Println("Cannot retrieve info for", p.url)
		}
		info := DownloadInfo{URL: p.url}
		json.Unmarshal(stdout, &info)
		p.mem.Update(p.id, info)
	}()

	// --------------- progress block --------------- //
	// unbuffered channel connected to stdout
	eventChan := make(chan string)

	// spawn a goroutine that does the dirty job of parsing the stdout
	// filling the channel with as many stdout line as yt-dlp produces (producer)
	go func() {
		defer r.Close()
		defer p.Complete()
		for scan.Scan() {
			eventChan <- scan.Text()
		}
		cmd.Wait()
	}()

	// do the unmarshal operation every 250ms (consumer)
	go rx.Debounce(time.Millisecond*250, eventChan, func(text string) {
		stdout := ProgressTemplate{}
		err := json.Unmarshal([]byte(text), &stdout)
		if err == nil {
			p.mem.UpdateProgress(p.id, DownloadProgress{
				Percentage: stdout.Percentage,
				Speed:      stdout.Speed,
				ETA:        stdout.Eta,
			})
			shortId := strings.Split(p.id, "-")[0]
			log.Printf("[%s] %s %s\n", shortId, p.url, p.Progress.Percentage)
		}
	})
	// ------------- end progress block ------------- //
}

// Keep process in the memoryDB but marks it as complete
// Convention: All completed processes has progress -1
// and speed 0 bps.
func (p *Process) Complete() {
	p.mem.UpdateProgress(p.id, DownloadProgress{
		Percentage: "-1",
		Speed:      0,
		ETA:        0,
	})
}

// Kill a process and remove it from the memory
func (p *Process) Kill() error {
	p.mem.Delete(p.id)
	// yt-dlp uses multiple child process the parent process
	// has been spawned with setPgid = true. To properly kill
	// all subprocesses a SIGTERM need to be sent to the correct
	// process group
	pgid, err := syscall.Getpgid(p.proc.Pid)
	if err != nil {
		return err
	}
	err = syscall.Kill(-pgid, syscall.SIGTERM)

	log.Println("Killed process", p.id)
	return err
}

// Returns the available format for this URL
func (p *Process) GetFormatsSync() (DownloadFormats, error) {
	cmd := exec.Command(cfg.GetConfig().DownloaderPath, p.url, "-J")
	stdout, err := cmd.Output()

	if err != nil {
		return DownloadFormats{}, err
	}

	cmd.Wait()

	info := DownloadFormats{URL: p.url}
	best := Format{}

	json.Unmarshal(stdout, &info)
	json.Unmarshal(stdout, &best)

	info.Best = best

	return info, nil
}