optimize readPacket (go-sql-driver#1705)

Avoid unnecessary allocation.

(cherry picked from commit 0fd55eb)

Author: rusher

compress_test.go

@@ -40,8 +40,6 @@ func uncompressHelper(t *testing.T, mc *mysqlConn, compressedPacket []byte) []by
 	conn := new(mockConn)
 	conn.data = compressedPacket
 	mc.netConn = conn
-	mc.readNextFunc = mc.compIO.readNext
-	mc.readFunc = conn.Read
 
 	uncompressedPacket, err := mc.readPacket()
 	if err != nil {

connection.go

@@ -40,8 +40,6 @@ type mysqlConn struct {
 	compressSequence      uint8
 	parseTime             bool
 	compress              bool
-	readFunc              func([]byte) (int, error)
-	readNextFunc          func(int, readerFunc) ([]byte, error)
 
 	// for context support (Go 1.8+)
 	watching bool
@@ -67,6 +65,16 @@ func (mc *mysqlConn) log(v ...any) {
 	mc.cfg.Logger.Print(v...)
 }
 
+func (mc *mysqlConn) readWithTimeout(b []byte) (int, error) {
+	to := mc.cfg.ReadTimeout
+	if to > 0 {
+		if err := mc.netConn.SetReadDeadline(time.Now().Add(to)); err != nil {
+			return 0, err
+		}
+	}
+	return mc.netConn.Read(b)
+}
+
 func (mc *mysqlConn) writeWithTimeout(b []byte) (int, error) {
 	to := mc.cfg.WriteTimeout
 	if to > 0 {

connection_test.go

@@ -27,8 +27,6 @@ func TestInterpolateParams(t *testing.T) {
 		cfg: &Config{
 			InterpolateParams: true,
 		},
-		readNextFunc: buf.readNext,
-		readFunc:     nc.Read,
 	}
 
 	q, err := mc.interpolateParams("SELECT ?+?", []driver.Value{int64(42), "gopher"})

connector.go

@@ -16,7 +16,6 @@ import (
 	"os"
 	"strconv"
 	"strings"
-	"time"
 )
 
 type connector struct {
@@ -131,22 +130,6 @@ func (c *connector) Connect(ctx context.Context) (driver.Conn, error) {
 
 	mc.buf = newBuffer()
 
-	// setting readNext/read functions
-	mc.readNextFunc = mc.buf.readNext
-
-	// Initialize read function based on configuration
-	if mc.cfg.ReadTimeout > 0 {
-		mc.readFunc = func(b []byte) (int, error) {
-			deadline := time.Now().Add(mc.cfg.ReadTimeout)
-			if err := mc.netConn.SetReadDeadline(deadline); err != nil {
-				return 0, err
-			}
-			return mc.netConn.Read(b)
-		}
-	} else {
-		mc.readFunc = mc.netConn.Read
-	}
-
 	// Reading Handshake Initialization Packet
 	authData, serverCapabilities, serverExtendedCapabilities, plugin, err := mc.readHandshakePacket()
 	if err != nil {
@@ -187,7 +170,6 @@ func (c *connector) Connect(ctx context.Context) (driver.Conn, error) {
 	if mc.cfg.compress && mc.clientCapabilities&clientCompress > 0 {
 		mc.compress = true
 		mc.compIO = newCompIO(mc)
-		mc.readNextFunc = mc.compIO.readNext
 	}
 	if mc.cfg.MaxAllowedPacket > 0 {
 		mc.maxAllowedPacket = mc.cfg.MaxAllowedPacket

packets.go

@@ -401,7 +401,6 @@ func (mc *mysqlConn) writeHandshakeResponsePacket(authResp []byte, serverCapabil
 			return err
 		}
 		mc.netConn = tlsConn
-		mc.readFunc = mc.netConn.Read
 	}
 
 	// User [null terminated string]

packets_test.go

@@ -106,8 +106,6 @@ func newRWMockConn(sequence uint8) (*mockConn, *mysqlConn) {
 		closech:          make(chan struct{}),
 		maxAllowedPacket: defaultMaxAllowedPacket,
 		sequence:         sequence,
-		readNextFunc:     buf.readNext,
-		readFunc:         conn.Read,
 	}
 	return conn, mc
 }
@@ -116,11 +114,9 @@ func TestReadPacketSingleByte(t *testing.T) {
 	conn := new(mockConn)
 	buf := newBuffer()
 	mc := &mysqlConn{
-		netConn:      conn,
-		buf:          buf,
-		cfg:          NewConfig(),
-		readNextFunc: buf.readNext,
-		readFunc:     conn.Read,
+		netConn: conn,
+		buf:     buf,
+		cfg:     NewConfig(),
 	}
 
 	conn.data = []byte{0x01, 0x00, 0x00, 0x00, 0xff}
@@ -173,11 +169,9 @@ func TestReadPacketSplit(t *testing.T) {
 	conn := new(mockConn)
 	buf := newBuffer()
 	mc := &mysqlConn{
-		netConn:      conn,
-		buf:          buf,
-		cfg:          NewConfig(),
-		readNextFunc: buf.readNext,
-		readFunc:     conn.Read,
+		netConn: conn,
+		buf:     buf,
+		cfg:     NewConfig(),
 	}
 
 	data := make([]byte, maxPacketSize*2+4*3)
@@ -283,12 +277,10 @@ func TestReadPacketFail(t *testing.T) {
 	conn := new(mockConn)
 	buf := newBuffer()
 	mc := &mysqlConn{
-		netConn:      conn,
-		buf:          buf,
-		closech:      make(chan struct{}),
-		cfg:          NewConfig(),
-		readNextFunc: buf.readNext,
-		readFunc:     conn.Read,
+		netConn: conn,
+		buf:     buf,
+		closech: make(chan struct{}),
+		cfg:     NewConfig(),
 	}
 
 	// illegal empty (stand-alone) packet
@@ -331,13 +323,11 @@ func TestRegression801(t *testing.T) {
 	conn := new(mockConn)
 	buf := newBuffer()
 	mc := &mysqlConn{
-		netConn:      conn,
-		buf:          buf,
-		cfg:          new(Config),
-		sequence:     42,
-		closech:      make(chan struct{}),
-		readNextFunc: buf.readNext,
-		readFunc:     conn.Read,
+		netConn:  conn,
+		buf:      buf,
+		cfg:      new(Config),
+		sequence: 42,
+		closech:  make(chan struct{}),
 	}
 
 	conn.data = []byte{72, 0, 0, 42, 10, 53, 46, 53, 46, 56, 0, 165, 0, 0, 0,