conncheck: use unix.Poll instead of syscall.Read

Author: methane

Diff for: conncheck.go

@@ -13,16 +13,16 @@ package mysql
 
 import (
 	"errors"
-	"io"
+	"fmt"
 	"net"
 	"syscall"
+
+	"golang.org/x/sys/unix"
 )
 
-var errUnexpectedRead = errors.New("unexpected read from socket")
+var errUnexpectedEvent = errors.New("recieved unexpected event")
 
 func connCheck(conn net.Conn) error {
-	var sysErr error
-
 	sysConn, ok := conn.(syscall.Conn)
 	if !ok {
 		return nil
@@ -32,24 +32,22 @@ func connCheck(conn net.Conn) error {
 		return err
 	}
 
-	err = rawConn.Read(func(fd uintptr) bool {
-		var buf [1]byte
-		n, err := syscall.Read(int(fd), buf[:])
-		switch {
-		case n == 0 && err == nil:
-			sysErr = io.EOF
-		case n > 0:
-			sysErr = errUnexpectedRead
-		case err == syscall.EAGAIN || err == syscall.EWOULDBLOCK:
-			sysErr = nil
-		default:
-			sysErr = err
+	var pollErr error
+	err = rawConn.Control(func(fd uintptr) {
+		fds := []unix.PollFd{
+			{Fd: int32(fd), Events: unix.POLLIN | unix.POLLERR},
+		}
+		n, err := unix.Poll(fds, 0)
+		if err != nil {
+			pollErr = fmt.Errorf("poll: %w", err)
+		}
+		if n > 0 {
+			// fmt.Errorf("poll: %v", fds[0].Revents)
+			pollErr = errUnexpectedEvent
 		}
-		return true
 	})
 	if err != nil {
 		return err
 	}
-
-	return sysErr
+	return pollErr
 }

Diff for: go.mod

@@ -1,3 +1,5 @@
 module github.com/go-sql-driver/mysql
 
 go 1.18
+
+require golang.org/x/sys v0.10.0 // indirect

Diff for: go.sum

@@ -0,0 +1,2 @@
+golang.org/x/sys v0.10.0 h1:SqMFp9UcQJZa+pmYuAKjd9xq1f0j5rLcDIk0mj4qAsA=
+golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

Diff for: packets.go

@@ -44,12 +44,24 @@ func (mc *mysqlConn) readPacket() ([]byte, error) {
 
 		// check packet sync [8 bit]
 		if data[3] != mc.sequence {
+			var syncErr error
 			if data[3] > mc.sequence {
-				return nil, ErrPktSyncMul
+				syncErr = ErrPktSyncMul
+			} else {
+				syncErr = ErrPktSync
 			}
-			return nil, ErrPktSync
+
+			if prevData != nil {
+				return nil, syncErr
+			} else {
+				// log and ignore seqno mismatch error.
+				// MySQL sometimes sends wrong sequence no.
+				mc.cfg.Logger.Print(syncErr)
+				mc.sequence = data[3] + 1
+			}
+		} else {
+			mc.sequence++
 		}
-		mc.sequence++
 
 		// packets with length 0 terminate a previous packet which is a
 		// multiple of (2^24)-1 bytes long
@@ -111,18 +123,29 @@ func (mc *mysqlConn) writePacket(data []byte) error {
 		}
 		var err error
 		if mc.cfg.CheckConnLiveness {
-			if mc.cfg.ReadTimeout != 0 {
-				err = conn.SetReadDeadline(time.Now().Add(mc.cfg.ReadTimeout))
-			}
-			if err == nil {
-				err = connCheck(conn)
+			err = connCheck(conn)
+			if err != nil {
+				if err == errUnexpectedEvent {
+					_ = conn.SetReadDeadline(time.Now().Add(time.Second))
+					var data []byte
+					data, err = mc.readPacket()
+
+					if err == nil {
+						if data[0] == iERR {
+							err = mc.handleErrorPacket(data)
+						} else {
+							err = fmt.Errorf("unexpected packet: % x", data[:128])
+						}
+					} else {
+						err = fmt.Errorf("readPacket(): %w", err)
+					}
+				}
+
+				mc.cfg.Logger.Print("checkConn() failed: ", err)
+				mc.Close()
+				return driver.ErrBadConn
 			}
 		}
-		if err != nil {
-			mc.cfg.Logger.Print("closing bad idle connection: ", err)
-			mc.Close()
-			return driver.ErrBadConn
-		}
 	}
 
 	for {