feat(pool): add check for badConnection

* fix: badConn check(#2053)

* fix: internalpool test

* fix: sentinel test

* fix: conncheck ut

* fix: remove maxBadConnRetries

* fix: add connCheck.deadline check

Signed-off-by: monkey92t <golang@88.com>

internal/pool/conn_check.go

@@ -0,0 +1,49 @@
+// +build linux darwin dragonfly freebsd netbsd openbsd solaris illumos
+
+package pool
+
+import (
+	"errors"
+	"io"
+	"net"
+	"syscall"
+	"time"
+)
+
+var errUnexpectedRead = errors.New("unexpected read from socket")
+
+func connCheck(conn net.Conn) error {
+	// Reset previous timeout.
+	_ = conn.SetDeadline(time.Time{})
+
+	sysConn, ok := conn.(syscall.Conn)
+	if !ok {
+		return nil
+	}
+	rawConn, err := sysConn.SyscallConn()
+	if err != nil {
+		return err
+	}
+
+	var sysErr error
+	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
+		}
+		return true
+	})
+	if err != nil {
+		return err
+	}
+
+	return sysErr
+}