magnet-to-torrent/main.go

package main

import (
	"context"
	"flag"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"regexp"
	"time"

	"github.com/anacrolix/torrent"
)

var invalidFilenameChars = regexp.MustCompile(`[<>:"/\\|?*\x00-\x1F]`)

// sanitizeFilename replaces invalid filesystem characters with underscores.
func sanitizeFilename(name string) string {
	return invalidFilenameChars.ReplaceAllString(name, "_")
}

func main() {
	// Command-line flags
	output := flag.String("o", "", "Output .torrent filename (optional)")
	timeout := flag.Duration("timeout", 5*time.Minute, "Timeout for metadata retrieval")
	upload := flag.Bool("upload", false, "Allow uploading (seeding) after metadata retrieval")

	flag.Usage = func() {
		fmt.Fprintf(flag.CommandLine.Output(), "Usage: %s [options] magnet_link\nOptions:\n", os.Args[0])
		flag.PrintDefaults()
	}
	flag.Parse()

	if flag.NArg() < 1 {
		flag.Usage()
		os.Exit(1)
	}
	magnetLink := flag.Arg(0)

	// Configure torrent client
	clientConfig := torrent.NewDefaultClientConfig()
	clientConfig.DataDir = os.TempDir()
	clientConfig.NoUpload = !*upload

	client, err := torrent.NewClient(clientConfig)
	if err != nil {
		log.Fatalf("Error creating torrent client: %v", err)
	}
	defer client.Close()

	// Add magnet link
	t, err := client.AddMagnet(magnetLink)
	if err != nil {
		log.Fatalf("Error adding magnet link: %v", err)
	}

	// Wait for metadata with timeout
	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
	defer cancel()

	select {
	case <-t.GotInfo():
		// Metadata received
	case <-ctx.Done():
		log.Fatalf("Timeout waiting for metadata after %v", *timeout)
	}

	info := t.Metainfo()

	// Determine output filename
	outFile := *output
	if outFile == "" {
		base := sanitizeFilename(t.Name())
		outFile = base + ".torrent"
	}
	outFile = filepath.Clean(outFile)

	// Write .torrent file
	f, err := os.Create(outFile)
	if err != nil {
		log.Fatalf("Error creating file %s: %v", outFile, err)
	}
	defer f.Close()

	if err := info.Write(f); err != nil {
		log.Fatalf("Error writing torrent file: %v", err)
	}

	fmt.Printf("Torrent metadata saved to %s\n", outFile)

	// Drop the torrent handle; client will close via defer
	t.Drop()
}