}
		if err := w.Close(); err != nil {
			t.Fatalf("Unable to write archive: %s", err)
		}

		// TODO: We may want to check if the archive roundtrips. This would require
		// taking into account addition of the two zero trailer blocks that Writer.Close
		// appends.
	})

	defer mu.Unlock()
	if u, frag, ok := strings.Cut(url, "#"); ok {
		url = u
		if frag != "" {
			uf := urlFrag{url, frag}
			neededFrags[uf] = append(neededFrags[uf], sourceURL)
		}
	}
	if crawled[url] {
		return
	}
	crawled[url] = true

	wg.Add(1)
	go func() {
		urlq <- url
	}()
}

func addProblem(url, errmsg string) {
	msg := fmt.Sprintf("Error on %s: %s (from %s)", url, errmsg, linkSources[url])

		return FormatUnknown
	}

	// Guess the magic values.
	magic := string(b.toUSTAR().magic())
	version := string(b.toUSTAR().version())
	trailer := string(b.toSTAR().trailer())
	switch {
	case magic == magicUSTAR && trailer == trailerSTAR:
		return formatSTAR
	case magic == magicUSTAR:
		return FormatUSTAR | FormatPAX
	case magic == magicGNU && version == versionGNU:
		return FormatGNU

pkg net/http, type Request struct, RemoteAddr string
pkg net/http, type Request struct, RequestURI string
pkg net/http, type Request struct, TLS *tls.ConnectionState
pkg net/http, type Request struct, Trailer Header
pkg net/http, type Request struct, TransferEncoding []string
pkg net/http, type Request struct, URL *url.URL
pkg net/http, type Response struct
pkg net/http, type Response struct, Body io.ReadCloser

pkg math/rand, type Source64 interface, Seed(int64)
pkg math/rand, type Source64 interface, Uint64() uint64
pkg net/http, const TrailerPrefix ideal-string
pkg net/http, const TrailerPrefix = "Trailer:"
pkg net/http/httptrace, type ClientTrace struct, TLSHandshakeDone func(tls.ConnectionState, error)
pkg net/http/httptrace, type ClientTrace struct, TLSHandshakeStart func()

// then this returns an error.
func (tw *Writer) Close() error {
	if tw.err == ErrWriteAfterClose {
		return nil
	}
	if tw.err != nil {
		return tw.err
	}

	// Trailer: two zero blocks.
	err := tw.Flush()
	for i := 0; i < 2 && err == nil; i++ {
		_, err = tw.w.Write(zeroBlock[:])
	}

	// Ensure all future actions are invalid.
	tw.err = ErrWriteAfterClose

pkg syscall (linux-386), const ETH_P_SNAP = 5
pkg syscall (linux-386), const ETH_P_TEB = 25944
pkg syscall (linux-386), const ETH_P_TIPC = 35018
pkg syscall (linux-386), const ETH_P_TRAILER = 28
pkg syscall (linux-386), const ETH_P_TR_802_2 = 17
pkg syscall (linux-386), const ETH_P_WAN_PPP = 7
pkg syscall (linux-386), const ETH_P_WCCP = 34878
pkg syscall (linux-386), const ETH_P_X25 = 2053

pkg image/draw, type Drawer interface { Draw }
pkg image/draw, type Drawer interface, Draw(Image, image.Rectangle, image.Image, image.Point)
pkg image/draw, type Quantizer interface { Quantize }
pkg image/draw, type Quantizer interface, Quantize(color.Palette, image.Image) color.Palette
pkg image/draw, var FloydSteinberg Drawer
pkg image/gif, func Encode(io.Writer, image.Image, *Options) error