return err
	}
	buf := bufio.NewReader(rs)

	// The count of files inside a zip is truncated to fit in a uint16.
	// Gloss over this by reading headers until we encounter
	// a bad one, and then only report an ErrFormat or UnexpectedEOF if
	// the file count modulo 65536 is incorrect.
	for {
		f := &File{zip: r, zipr: rdr}
		err = readDirectoryHeader(f, buf)
		if err == ErrFormat || err == io.ErrUnexpectedEOF {

// then readFrom uses Seek to skip past holes defined in Header.SparseHoles,
// assuming that skipped regions are all NULs.
// This always reads the last byte to ensure r is the right size.
//
// TODO(dsnet): Re-export this when adding sparse file support.
// See https://golang.org/issue/22735
func (tw *Writer) readFrom(r io.Reader) (int64, error) {
	if tw.err != nil {
		return 0, tw.err
	}
	n, err := tw.curr.ReadFrom(r)

that returns errno.

# C references to Go

Go functions can be exported for use by C code in the following way:

	//export MyFunction
	func MyFunction(arg1, arg2 int, arg3 string) int64 {...}

	//export MyFunction2
	func MyFunction2(arg1, arg2 int, arg3 string) (int64, *C.char) {...}

They will be available in the C code as:

	if n.Doc == nil {
		return
	}
	for _, c := range n.Doc.List {
		if !strings.HasPrefix(c.Text, "//export ") {
			continue
		}

		name := strings.TrimSpace(c.Text[9:])
		if name == "" {
			error_(c.Pos(), "export missing name")
		}

		if name != n.Name.Name {
			error_(c.Pos(), "export comment has wrong name %q, want %q", name, n.Name.Name)
		}

		doc := ""
		for _, c1 := range n.Doc.List {

		}
	}()
	cmd := `export TMPDIR="` + deviceGotmp + `"` +
		`; export GOROOT="` + deviceGoroot + `"` +
		`; export GOPATH="` + deviceGopath + `"` +
		`; export CGO_ENABLED=0` +
		`; export GOPROXY=` + os.Getenv("GOPROXY") +
		`; export GOCACHE="` + deviceRoot + `/gocache"` +
		`; export PATH="` + deviceGoroot + `/bin":$PATH` +
		`; export HOME="` + deviceRoot + `/home"` +
		`; cd "` + deviceCwd + `"` +

	if exitCode == 1 {
		t.Errorf("API database problems found")
	}
	if !compareAPI(bw, features, required, exception) {
		t.Errorf("API differences found")
	}
}

// export emits the exported package features.
func (w *Walker) export(pkg *apiPackage) {
	if verbose {
		log.Println(pkg)
	}
	pop := w.pushScope("pkg " + pkg.Path())
	w.current = pkg
	w.collectDeprecated()
	scope := pkg.Scope()

// then writeTo uses Seek to skip past holes defined in Header.SparseHoles,
// assuming that skipped regions are filled with NULs.
// This always writes the last byte to ensure w is the right size.
//
// TODO(dsnet): Re-export this when adding sparse file support.
// See https://golang.org/issue/22735
func (tr *Reader) writeTo(w io.Writer) (int64, error) {
	if tr.err != nil {
		return 0, tr.err
	}
	n, err := tr.curr.WriteTo(w)