Add BEP 19 web seed support (url-list) to torrent creation

cmd/wl/main.go

@@ -64,6 +64,8 @@ func main() {
 		category := createCmd.String("category", "", "Category (e.g. models, datasets)")
 		tags := createCmd.String("tags", "", "Comma-separated tags")
 		comment := createCmd.String("comment", "", "Optional comment in the torrent file")
+		var webseeds stringSlice
+		createCmd.Var(&webseeds, "webseed", "BEP 19 web seed URL (HTTP origin fallback); repeatable")
 		createCmd.Parse(os.Args[2:])
 
 		path := createCmd.Arg(0)
@@ -86,6 +88,7 @@ func main() {
 			category:    *category,
 			tags:        *tags,
 			comment:     *comment,
+			webseeds:    webseeds,
 		}
 
 		if err := runCreate(opts); err != nil {
@@ -135,6 +138,16 @@ type createOpts struct {
 	category    string
 	tags        string
 	comment     string
+	webseeds    []string
+}
+
+// stringSlice is a repeatable string flag (e.g. --webseed a --webseed b).
+type stringSlice []string
+
+func (s *stringSlice) String() string { return strings.Join(*s, ",") }
+func (s *stringSlice) Set(v string) error {
+	*s = append(*s, v)
+	return nil
 }
 
 func runCreate(opts createOpts) error {
@@ -160,6 +173,7 @@ func runCreate(opts createOpts) error {
 		Comment:     opts.comment,
 		Source:      envOr("WL_SOURCE", ""),
 		CreatedBy:   envOr("WL_CREATED_BY", ""),
+		WebSeeds:    opts.webseeds,
 	})
 	if err != nil {
 		return fmt.Errorf("create torrent: %w", err)

internal/torrent/torrent.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"math/bits"
+	"net/url"
 	"os"
 	"path/filepath"
 	"sort"
@@ -24,14 +25,15 @@ const (
 
 // CreateOptions configures torrent creation.
 type CreateOptions struct {
-	Path        string // file or directory to torrent
-	Name        string // torrent name (defaults to basename of Path)
-	PieceLength int    // must be power of 2, >= MinPieceLength
-	AnnounceURL string // tracker announce URL
-	Private     bool   // if true, disables DHT/PEX (BEP 27)
-	Comment     string // optional comment
-	Source      string // source tag in info dict (e.g. "weightless.ai")
-	CreatedBy   string // created by field (e.g. "Weightless CLI v1.0")
+	Path        string   // file or directory to torrent
+	Name        string   // torrent name (defaults to basename of Path)
+	PieceLength int      // must be power of 2, >= MinPieceLength
+	AnnounceURL string   // tracker announce URL
+	Private     bool     // if true, disables DHT/PEX (BEP 27)
+	Comment     string   // optional comment
+	Source      string   // source tag in info dict (e.g. "weightless.ai")
+	CreatedBy   string   // created by field (e.g. "Weightless CLI v1.0")
+	WebSeeds    []string // BEP 19 web seed URLs (top-level url-list; HTTP origin fallback)
 }
 
 // CreateResult holds the output of torrent creation.
@@ -64,6 +66,12 @@ func Create(opts CreateOptions) (*CreateResult, error) {
 	if opts.PieceLength < MinPieceLength || !isPowerOfTwo(opts.PieceLength) {
 		return nil, fmt.Errorf("piece length must be a power of 2 and >= %d, got %d", MinPieceLength, opts.PieceLength)
 	}
+	for _, ws := range opts.WebSeeds {
+		u, err := url.Parse(ws)
+		if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
+			return nil, fmt.Errorf("web seed must be an absolute http(s) URL, got %q", ws)
+		}
+	}
 
 	info, err := os.Stat(opts.Path)
 	if err != nil {
@@ -108,6 +116,11 @@ func Create(opts CreateOptions) (*CreateResult, error) {
 	if len(pieceLayers) > 0 {
 		metaDict.set("piece layers", pieceLayers)
 	}
+	// BEP 19 web seeds (top-level, outside the info dict so the info hash is
+	// unaffected). Clients fall back to these HTTP origins when peers are scarce.
+	if len(opts.WebSeeds) > 0 {
+		metaDict.set("url-list", opts.WebSeeds)
+	}
 
 	torrentBytes, err := bencode.EncodeBytes(metaDict)
 	if err != nil {

internal/torrent/torrent_test.go

@@ -147,6 +147,76 @@ func TestHybridGoldenVectors(t *testing.T) {
 	}
 }
 
+func TestCreateWebSeeds(t *testing.T) {
+	t.Parallel()
+	dir := t.TempDir()
+	path := filepath.Join(dir, "data.bin")
+	data := make([]byte, 64*1024)
+	for i := range data {
+		data[i] = byte(i % 256)
+	}
+	if err := os.WriteFile(path, data, 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	base := CreateOptions{
+		Path:        path,
+		Name:        "data.bin",
+		PieceLength: 16 * 1024,
+		AnnounceURL: "http://localhost:8080/announce",
+	}
+
+	// Without web seeds: no url-list key, capture baseline hashes.
+	plain, err := Create(base)
+	if err != nil {
+		t.Fatalf("Create (plain) failed: %v", err)
+	}
+	var plainMeta map[string]interface{}
+	if err := bencode.DecodeBytes(plain.TorrentBytes, &plainMeta); err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := plainMeta["url-list"]; ok {
+		t.Error("url-list should be absent when no web seeds are given")
+	}
+
+	// With web seeds: url-list present (top-level), info hashes UNCHANGED.
+	seeds := []string{"https://example.com/data.bin", "http://mirror.example.org/data.bin"}
+	ws := base
+	ws.WebSeeds = seeds
+	result, err := Create(ws)
+	if err != nil {
+		t.Fatalf("Create (webseed) failed: %v", err)
+	}
+	if result.InfoHashHex != plain.InfoHashHex || result.InfoHashV1Hex != plain.InfoHashV1Hex {
+		t.Error("web seeds must not change the info hash (url-list is outside the info dict)")
+	}
+
+	var meta map[string]interface{}
+	if err := bencode.DecodeBytes(result.TorrentBytes, &meta); err != nil {
+		t.Fatal(err)
+	}
+	raw, ok := meta["url-list"].([]interface{})
+	if !ok {
+		t.Fatalf("url-list missing or not a list: %T", meta["url-list"])
+	}
+	got := make([]string, len(raw))
+	for i, v := range raw {
+		got[i] = v.(string)
+	}
+	if len(got) != 2 || got[0] != seeds[0] || got[1] != seeds[1] {
+		t.Errorf("url-list = %v, want %v", got, seeds)
+	}
+
+	// Invalid web seed URLs are rejected at the boundary.
+	for _, bad := range []string{"not-a-url", "ftp://x/y", "/relative/path", "https://"} {
+		bw := base
+		bw.WebSeeds = []string{bad}
+		if _, err := Create(bw); err == nil {
+			t.Errorf("Create accepted invalid web seed %q", bad)
+		}
+	}
+}
+
 func TestCreateSingleFileHybrid(t *testing.T) {
 	dir := t.TempDir()
 	path := filepath.Join(dir, "test.dat")