msg       string // description of error
	context   string // additional error context
	pos       errPos
	atChar    byte
	readerErr error // underlying reader error, if any
}

// ReaderErr returns the underlying error.
func (e DecoderError) ReaderErr() error { return e.readerErr }

// Error returns a string representation of the error.
func (e DecoderError) Error() string {

		want    string
		wantpos int64
		readerr error
		seekerr string
	}{
		{seek: io.SeekStart, off: 0, n: 20, want: "0123456789"},
		{seek: io.SeekStart, off: 1, n: 1, want: "1"},
		{seek: io.SeekCurrent, off: 1, wantpos: 3, n: 2, want: "34"},
		{seek: io.SeekStart, off: -1, seekerr: "bytes.Reader.Seek: negative position"},
		{seek: io.SeekStart, off: 1 << 33, wantpos: 1 << 33, readerr: io.EOF},

	var i int
	r := bytes.NewReader(data)
	scanner := newScanner(r)
	for scanner.pos < atomic.LoadInt64(&scanner.end) {
		c := scanner.next()
		if scanner.readerErr != nil {
			t.Fatal(scanner.readerErr)
		}
		if c != data[i] {
			t.Fatalf("expected %s, got %s", string(data[i]), string(c))
		}
		t.Logf("pos=%d remaining=%d (%s)", i, r.Len(), string(c))
		i++
	}
}

	end       int64
	buf       [chunk + 1]byte // internal buffer (with a lookback size of 1)
	nbuf      [chunk]byte     // next internal buffer
	fillReq   chan struct{}
	fillReady chan int64
	readerErr error // underlying reader error, if any
}

func newScanner(r io.Reader) *scanner {
	sr := &scanner{
		end:       maxInt,
		fillReq:   make(chan struct{}),
		fillReady: make(chan int64),
	}

	go func() {

	if err == nil {
		t.Fatalf("missing expected decoder error")
	}

	derr, ok := err.(DecoderError)
	if !ok {
		t.Fatalf("expected error of type DecoderError, got %T", err)
	}

	if derr.ReaderErr() == nil {
		t.Fatalf("missing expected underlying reader error")
	}
}

func TestDecoderMaxDepth(t *testing.T) {
	tests := []struct {
		input    string
		maxDepth int
		mustFail bool
	}{