Reduce allocations and copies in pgproto3

Altered chunkreader to never reuse memory.

Altered pgproto3 to to copy memory when decoding. Renamed UnmarshalBinary to
Decode because of changed semantics.

chunkreader.go

@@ -9,14 +9,12 @@ type ChunkReader struct {
 
 	buf    []byte
 	rp, wp int // buf read position and write position
-	taken  bool
 
 	options Options
 }
 
 type Options struct {
 	MinBufLen int // Minimum buffer length
-	BlockLen  int // Increments to expand buffer (e.g. a 8000 byte request with a BlockLen of 1024 would yield a buffer len of 8192)
 }
 
 func NewChunkReader(r io.Reader) *ChunkReader {
@@ -32,9 +30,6 @@ func NewChunkReaderEx(r io.Reader, options Options) (*ChunkReader, error) {
 	if options.MinBufLen == 0 {
 		options.MinBufLen = 4096
 	}
-	if options.BlockLen == 0 {
-		options.BlockLen = 512
-	}
 
 	return &ChunkReader{
 		r:       r,
@@ -43,8 +38,8 @@ func NewChunkReaderEx(r io.Reader, options Options) (*ChunkReader, error) {
 	}, nil
 }
 
-// Next returns buf filled with the next n bytes. buf is only valid until the
+// Next returns buf filled with the next n bytes. If an error occurs, buf will
-// next call to Next. If an error occurs, buf will be nil.
+// be nil.
 func (r *ChunkReader) Next(n int) (buf []byte, err error) {
 	// n bytes already in buf
 	if (r.wp - r.rp) >= n {
@@ -56,17 +51,12 @@ func (r *ChunkReader) Next(n int) (buf []byte, err error) {
 	// available space in buf is less than n
 	if len(r.buf) < n {
 		r.copyBufContents(r.newBuf(n))
-		r.taken = false
 	}
 
 	// buf is large enough, but need to shift filled area to start to make enough contiguous space
 	minReadCount := n - (r.wp - r.rp)
 	if (len(r.buf) - r.wp) < minReadCount {
-		newBuf := r.buf
+		newBuf := r.newBuf(n)
-		if r.taken {
-			newBuf = r.newBuf(n)
-			r.taken = false
-		}
 		r.copyBufContents(newBuf)
 	}
 
@@ -79,20 +69,13 @@ func (r *ChunkReader) Next(n int) (buf []byte, err error) {
 	return buf, nil
 }
 
-// KeepLast prevents the last data retrieved by Next from being reused by the
-// ChunkReader.
-func (r *ChunkReader) KeepLast() {
-	r.taken = true
-}
-
 func (r *ChunkReader) appendAtLeast(fillLen int) error {
 	n, err := io.ReadAtLeast(r.r, r.buf[r.wp:], fillLen)
 	r.wp += n
 	return err
 }
 
-func (r *ChunkReader) newBuf(min int) []byte {
+func (r *ChunkReader) newBuf(size int) []byte {
-	size := ((min / r.options.BlockLen) + 1) * r.options.BlockLen
 	if size < r.options.MinBufLen {
 		size = r.options.MinBufLen
 	}

chunkreader_test.go

@@ -7,7 +7,7 @@ import (
 
 func TestChunkReaderNextDoesNotReadIfAlreadyBuffered(t *testing.T) {
 	server := &bytes.Buffer{}
-	r, err := NewChunkReaderEx(server, Options{MinBufLen: 4, BlockLen: 2})
+	r, err := NewChunkReaderEx(server, Options{MinBufLen: 4})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -44,7 +44,7 @@ func TestChunkReaderNextDoesNotReadIfAlreadyBuffered(t *testing.T) {
 
 func TestChunkReaderNextExpandsBufAsNeeded(t *testing.T) {
 	server := &bytes.Buffer{}
-	r, err := NewChunkReaderEx(server, Options{MinBufLen: 4, BlockLen: 2})
+	r, err := NewChunkReaderEx(server, Options{MinBufLen: 4})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -59,14 +59,14 @@ func TestChunkReaderNextExpandsBufAsNeeded(t *testing.T) {
 	if bytes.Compare(n1, src[0:5]) != 0 {
 		t.Fatalf("Expected read bytes to be %v, but they were %v", src[0:5], n1)
 	}
-	if len(r.buf) != 6 {
+	if len(r.buf) != 5 {
-		t.Fatalf("Expected len(r.buf) to be %v, but it was %v", 6, len(r.buf))
+		t.Fatalf("Expected len(r.buf) to be %v, but it was %v", 5, len(r.buf))
 	}
 }
 
-func TestChunkReaderNextReusesBuf(t *testing.T) {
+func TestChunkReaderDoesNotReuseBuf(t *testing.T) {
 	server := &bytes.Buffer{}
-	r, err := NewChunkReaderEx(server, Options{MinBufLen: 4, BlockLen: 1})
+	r, err := NewChunkReaderEx(server, Options{MinBufLen: 4})
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -90,38 +90,6 @@ func TestChunkReaderNextReusesBuf(t *testing.T) {
 		t.Fatalf("Expected read bytes to be %v, but they were %v", src[4:8], n2)
 	}
 
-	if bytes.Compare(n1, src[4:8]) != 0 {
-		t.Fatalf("Expected Next to have reused buf, %v found instead of %v", src[4:8], n1)
-	}
-}
-
-func TestChunkReaderKeepLastPreventsBufReuse(t *testing.T) {
-	server := &bytes.Buffer{}
-	r, err := NewChunkReaderEx(server, Options{MinBufLen: 4, BlockLen: 1})
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	src := []byte{1, 2, 3, 4, 5, 6, 7, 8}
-	server.Write(src)
-
-	n1, err := r.Next(4)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if bytes.Compare(n1, src[0:4]) != 0 {
-		t.Fatalf("Expected read bytes to be %v, but they were %v", src[0:4], n1)
-	}
-	r.KeepLast()
-
-	n2, err := r.Next(4)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if bytes.Compare(n2, src[4:8]) != 0 {
-		t.Fatalf("Expected read bytes to be %v, but they were %v", src[4:8], n2)
-	}
-
 	if bytes.Compare(n1, src[0:4]) != 0 {
 		t.Fatalf("Expected KeepLast to prevent Next from overwriting buf, expected %v but it was %v", src[0:4], n1)
 	}