From 37fd83174fd6523cf0d9e56ef20d6725ab25718e Mon Sep 17 00:00:00 2001
From: INADA Naoki <songofacandy@gmail.com>
Date: Tue, 13 Nov 2018 18:18:05 +0900
Subject: [PATCH 1/2] buffer: Improve cap consistency.

---
 buffer.go  | 20 ++++++++++++++------
 packets.go |  2 +-
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/buffer.go b/buffer.go
index eb4748bf4..2dc27cbf5 100644
--- a/buffer.go
+++ b/buffer.go
@@ -30,9 +30,8 @@ type buffer struct {
 }
 
 func newBuffer(nc net.Conn) buffer {
-	var b [defaultBufSize]byte
 	return buffer{
-		buf: b[:],
+		buf: make([]byte, defaultBufSize, defaultBufSize),
 		nc:  nc,
 	}
 }
@@ -51,7 +50,8 @@ func (b *buffer) fill(need int) error {
 	//       Maybe keep the org buf slice and swap back?
 	if need > len(b.buf) {
 		// Round up to the next multiple of the default size
-		newBuf := make([]byte, ((need/defaultBufSize)+1)*defaultBufSize)
+		newSize := ((need / defaultBufSize) + 1) * defaultBufSize
+		newBuf := make([]byte, newSize, newSize)
 		copy(newBuf, b.buf)
 		b.buf = newBuf
 	}
@@ -114,13 +114,12 @@ func (b *buffer) takeBuffer(length int) []byte {
 		return nil
 	}
 
-	// test (cheap) general case first
-	if length <= defaultBufSize || length <= cap(b.buf) {
+	if length <= len(b.buf) {
 		return b.buf[:length]
 	}
 
 	if length < maxPacketSize {
-		b.buf = make([]byte, length)
+		b.buf = make([]byte, length, length)
 		return b.buf
 	}
 	return make([]byte, length)
@@ -145,3 +144,12 @@ func (b *buffer) takeCompleteBuffer() []byte {
 	}
 	return b.buf
 }
+
+// setGrownBuffer set buf as internal buffer if cap(buf) is larger
+// than len(b.buf).  It can be used when you took buffer by
+// takeCompleteBuffer and append some data to it.
+func (b *buffer) setGrownBuffer(buf []byte) {
+	if cap(buf) >= len(b.buf) {
+		b.buf = buf[:cap(buf)]
+	}
+}
diff --git a/packets.go b/packets.go
index 9ed640850..527488319 100644
--- a/packets.go
+++ b/packets.go
@@ -1076,7 +1076,7 @@ func (stmt *mysqlStmt) writeExecutePacket(args []driver.Value) error {
 		// In that case we must build the data packet with the new values buffer
 		if valuesCap != cap(paramValues) {
 			data = append(data[:pos], paramValues...)
-			mc.buf.buf = data
+			mc.buf.setGrownBuffer(data)
 		}
 
 		pos += len(paramValues)

From c189d6a99adbb793bbcc7279b153bcd22e78f0b3 Mon Sep 17 00:00:00 2001
From: INADA Naoki <songofacandy@gmail.com>
Date: Tue, 13 Nov 2018 18:38:17 +0900
Subject: [PATCH 2/2] cap(make([]byte, n)) == n

https://golang.org/ref/spec#Making_slices_maps_and_channels
---
 buffer.go | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/buffer.go b/buffer.go
index 2dc27cbf5..4d705a5a6 100644
--- a/buffer.go
+++ b/buffer.go
@@ -31,7 +31,7 @@ type buffer struct {
 
 func newBuffer(nc net.Conn) buffer {
 	return buffer{
-		buf: make([]byte, defaultBufSize, defaultBufSize),
+		buf: make([]byte, defaultBufSize),
 		nc:  nc,
 	}
 }
@@ -50,8 +50,7 @@ func (b *buffer) fill(need int) error {
 	//       Maybe keep the org buf slice and swap back?
 	if need > len(b.buf) {
 		// Round up to the next multiple of the default size
-		newSize := ((need / defaultBufSize) + 1) * defaultBufSize
-		newBuf := make([]byte, newSize, newSize)
+		newBuf := make([]byte, ((need/defaultBufSize)+1)*defaultBufSize)
 		copy(newBuf, b.buf)
 		b.buf = newBuf
 	}
@@ -119,7 +118,7 @@ func (b *buffer) takeBuffer(length int) []byte {
 	}
 
 	if length < maxPacketSize {
-		b.buf = make([]byte, length, length)
+		b.buf = make([]byte, length)
 		return b.buf
 	}
 	return make([]byte, length)
@@ -149,7 +148,9 @@ func (b *buffer) takeCompleteBuffer() []byte {
 // than len(b.buf).  It can be used when you took buffer by
 // takeCompleteBuffer and append some data to it.
 func (b *buffer) setGrownBuffer(buf []byte) {
-	if cap(buf) >= len(b.buf) {
-		b.buf = buf[:cap(buf)]
+	// buf may be grown by `buf = append(buf, ...)`.  So set len=cap explicitly.
+	buf = buf[:cap(buf)]
+	if len(buf) > len(b.buf) {
+		b.buf = buf
 	}
 }