Optimize decoding

gen.go

@@ -589,16 +589,14 @@ func emitCborUnmarshalStructField(w io.Writer, f Field) error {
 		return doTemplate(w, f, `
 	{
 {{ if .Pointer }}
-		pb, err := br.PeekByte()
+		b, err := br.ReadByte()
 		if err != nil {
 			return err
 		}
-		if pb == cbg.CborNull[0] {
-			var nbuf [1]byte
-			if _, err := br.Read(nbuf[:]); err != nil {
+		if b != cbg.CborNull[0] {
+			if err := br.UnreadByte(); err != nil {
 				return err
 			}
-		} else {
 {{ end }}
 		c, err := cbg.ReadCid(br)
 		if err != nil {
@@ -628,16 +626,14 @@ func emitCborUnmarshalStructField(w io.Writer, f Field) error {
 		return doTemplate(w, f, `
 	{
 {{ if .Pointer }}
-		pb, err := br.PeekByte()
+		b, err := br.ReadByte()
 		if err != nil {
 			return err
 		}
-		if pb == cbg.CborNull[0] {
-			var nbuf [1]byte
-			if _, err := br.Read(nbuf[:]); err != nil {
+		if b != cbg.CborNull[0] {
+			if err := br.UnreadByte(); err != nil {
 				return err
 			}
-		} else {
 			{{ .Name }} = new({{ .TypeName }})
 			if err := {{ .Name }}.UnmarshalCBOR(br); err != nil {
 				return xerrors.Errorf("unmarshaling {{ .Name }} pointer: %w", err)
@@ -685,16 +681,14 @@ func emitCborUnmarshalUint64Field(w io.Writer, f Field) error {
 	return doTemplate(w, f, `
 	{
 {{ if .Pointer }}
-	pb, err := br.PeekByte()
+	b, err := br.ReadByte()
 	if err != nil {
 		return err
 	}
-	if pb == cbg.CborNull[0] {
-		var nbuf [1]byte
-		if _, err := br.Read(nbuf[:]); err != nil {
+	if b != cbg.CborNull[0] {
+		if err := br.UnreadByte(); err != nil {
 			return err
 		}
-	} else {
 		maj, extra, err = {{ ReadHeader "br" }}
 		if err != nil {
 			return err

peeker.go

@@ -0,0 +1,80 @@
+package typegen
+
+import (
+	"bufio"
+	"io"
+)
+
+// BytePeeker combines the Reader and ByteScanner interfaces.
+type BytePeeker interface {
+	io.Reader
+	io.ByteScanner
+}
+
+func GetPeeker(r io.Reader) BytePeeker {
+	if r, ok := r.(BytePeeker); ok {
+		return r
+	}
+	return &peeker{reader: r}
+}
+
+// peeker is a non-buffering BytePeeker.
+type peeker struct {
+	reader    io.Reader
+	peekState int
+	lastByte  byte
+}
+
+const (
+	peekEmpty = iota
+	peekSet
+	peekUnread
+)
+
+func (p *peeker) Read(buf []byte) (n int, err error) {
+	// Read "nothing". I.e., read an error, maybe.
+	if len(buf) == 0 {
+		// There's something pending in the
+		if p.peekState == peekUnread {
+			return 0, nil
+		}
+		return p.reader.Read(nil)
+	}
+
+	if p.peekState == peekUnread {
+		buf[0] = p.lastByte
+		n, err = p.reader.Read(buf[1:])
+		n += 1
+	} else {
+		n, err = p.reader.Read(buf)
+	}
+	if n > 0 {
+		p.peekState = peekSet
+		p.lastByte = buf[n-1]
+	}
+	return n, err
+}
+
+func (p *peeker) ReadByte() (byte, error) {
+	if p.peekState == peekUnread {
+		p.peekState = peekSet
+		return p.lastByte, nil
+	}
+	var buf [1]byte
+	n, err := p.reader.Read(buf[:])
+	if n == 0 {
+		return 0, err
+	}
+	b := buf[0]
+	p.lastByte = b
+	p.peekState = peekSet
+	return b, err
+}
+
+func (p *peeker) UnreadByte() error {
+	if p.peekState != peekSet {
+		return bufio.ErrInvalidUnreadByte
+	}
+	p.peekState = peekUnread
+	return nil
+}

peeker_test.go

@@ -0,0 +1,103 @@
+package typegen
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"testing"
+)
+
+func TestPeeker(t *testing.T) {
+	buf := bytes.NewBuffer([]byte{0, 1, 2, 3})
+	p := peeker{reader: buf}
+	n, err := p.Read(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 0 {
+		t.Fatal(err)
+	}
+
+	err = p.UnreadByte()
+	if err != bufio.ErrInvalidUnreadByte {
+		t.Fatal(err)
+	}
+
+	// read 2 bytes
+	var out [2]byte
+	n, err = p.Read(out[:])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 2 {
+		t.Fatalf("expected 2 bytes, got %d", n)
+	}
+	if !bytes.Equal(out[:], []byte{0, 1}) {
+		t.Fatalf("unexpected output")
+	}
+
+	// unread that last byte and read it again.
+	err = p.UnreadByte()
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, err := p.ReadByte()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if b != 1 {
+		t.Fatal("expected 1")
+	}
+
+	// unread that last byte then read 2
+	err = p.UnreadByte()
+	if err != nil {
+		t.Fatal(err)
+	}
+	n, err = p.Read(out[:])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 2 {
+		t.Fatalf("expected 2 bytes, got %d", n)
+	}
+	if !bytes.Equal(out[:], []byte{1, 2}) {
+		t.Fatalf("unexpected output")
+	}
+
+	// read another byte
+	b, err = p.ReadByte()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if b != 3 {
+		t.Fatal("expected 1")
+	}
+
+	// Should read eof at end.
+	n, err = p.Read(out[:])
+	if err != io.EOF {
+		t.Fatal(err)
+	}
+	if n != 0 {
+		t.Fatal("should have been at end")
+	}
+	// should unread eof
+	err = p.UnreadByte()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = p.Read(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	b, err = p.ReadByte()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if b != 3 {
+		t.Fatal("expected 1")
+	}
+}

testing/bench_test.go

@@ -2,7 +2,6 @@ package testing
 
 import (
 	"bytes"
-	"encoding/hex"
 	"io"
 	"io/ioutil"
 	"math/rand"
@@ -34,21 +33,28 @@ func BenchmarkMarshaling(b *testing.B) {
 }
 
 func BenchmarkUnmarshaling(b *testing.B) {
-	hx := "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"
+	r := rand.New(rand.NewSource(123456))
+	val, ok := quick.Value(reflect.TypeOf(SimpleTypeTwo{}), r)
+	if !ok {
+		b.Fatal("failed to construct type")
+	}
 
-	d, err := hex.DecodeString(hx)
-	if err != nil {
+	tt := val.Interface().(SimpleTypeTwo)
+
+	buf := new(bytes.Buffer)
+	if err := tt.MarshalCBOR(buf); err != nil {
 		b.Fatal(err)
 	}
 
-	buf := bytes.NewReader(d)
+	reader := bytes.NewReader(buf.Bytes())
+
 	b.ReportAllocs()
 	b.ResetTimer()
 
 	for i := 0; i < b.N; i++ {
-		buf.Seek(0, io.SeekStart)
+		reader.Seek(0, io.SeekStart)
 		var tt SimpleTypeTwo
-		if err := tt.UnmarshalCBOR(buf); err != nil {
+		if err := tt.UnmarshalCBOR(reader); err != nil {
 			b.Fatal(err)
 		}
 	}
@@ -69,11 +75,44 @@ func BenchmarkLinkScan(b *testing.B) {
 		b.Fatal(err)
 	}
 
+	reader := bytes.NewReader(buf.Bytes())
+
 	b.ReportAllocs()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		reader.Seek(0, io.SeekStart)
+		if err := cbg.ScanForLinks(reader, func(cid.Cid) {}); err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
+func BenchmarkDeferred(b *testing.B) {
+	r := rand.New(rand.NewSource(123456))
+	val, ok := quick.Value(reflect.TypeOf(SimpleTypeTwo{}), r)
+	if !ok {
+		b.Fatal("failed to construct type")
+	}
+
+	tt := val.Interface().(SimpleTypeTwo)
+
+	buf := new(bytes.Buffer)
+	if err := tt.MarshalCBOR(buf); err != nil {
+		b.Fatal(err)
+	}
+
+	var (
+		deferred cbg.Deferred
+		reader   = bytes.NewReader(buf.Bytes())
+	)
+
 	b.ReportAllocs()
+	b.ResetTimer()
 
 	for i := 0; i < b.N; i++ {
-		if err := cbg.ScanForLinks(bytes.NewReader(buf.Bytes()), func(cid.Cid) {}); err != nil {
+		reader.Seek(0, io.SeekStart)
+		if err := deferred.UnmarshalCBOR(reader); err != nil {
 			b.Fatal(err)
 		}
 	}