Fix error usages

Author: nekohasekai

stack_gvisor_lazy.go

@@ -4,6 +4,7 @@ package tun
 
 import (
 	"context"
+	"errors"
 	"net"
 	"os"
 	"sync"
@@ -79,7 +80,7 @@ func (c *gLazyConn) HandshakeFailure(err error) error {
 	if c.handshakeDone {
 		return os.ErrInvalid
 	}
-	c.request.Complete(err != ErrDrop)
+	c.request.Complete(!errors.Is(err, ErrDrop))
 	c.handshakeDone = true
 	c.handshakeErr = err
 	return nil

stack_gvisor_tcp.go

@@ -4,6 +4,7 @@ package tun
 
 import (
 	"context"
+	"errors"
 
 	"github.com/sagernet/gvisor/pkg/tcpip/stack"
 	"github.com/sagernet/gvisor/pkg/tcpip/transport/tcp"
@@ -37,7 +38,7 @@ func (f *TCPForwarder) Forward(r *tcp.ForwarderRequest) {
 	destination := M.SocksaddrFrom(AddrFromAddress(r.ID().LocalAddress), r.ID().LocalPort)
 	pErr := f.handler.PrepareConnection(N.NetworkTCP, source, destination)
 	if pErr != nil {
-		r.Complete(pErr != ErrDrop)
+		r.Complete(!errors.Is(pErr, ErrDrop))
 		return
 	}
 	conn := &gLazyConn{

stack_gvisor_udp.go

@@ -4,6 +4,7 @@ package tun
 
 import (
 	"context"
+	"errors"
 	"math"
 	"net/netip"
 	"os"
@@ -59,7 +60,7 @@ func rangeIterate(r stack.Range, fn func(*buffer.View))
 func (f *UDPForwarder) PreparePacketConnection(source M.Socksaddr, destination M.Socksaddr, userData any) (bool, context.Context, N.PacketWriter, N.CloseHandlerFunc) {
 	pErr := f.handler.PrepareConnection(N.NetworkUDP, source, destination)
 	if pErr != nil {
-		if pErr != ErrDrop {
+		if !errors.Is(pErr, ErrDrop) {
 			gWriteUnreachable(f.stack, userData.(*stack.PacketBuffer))
 		}
 		return false, nil, nil, nil

stack_system.go

@@ -2,6 +2,7 @@ package tun
 
 import (
 	"context"
+	"errors"
 	"net"
 	"net/netip"
 	"syscall"
@@ -354,7 +355,7 @@ func (s *System) processIPv4TCP(ipHdr header.IPv4, tcpHdr header.TCP) (bool, err
 	} else {
 		natPort, err := s.tcpNat.Lookup(source, destination, s.handler)
 		if err != nil {
-			if err == ErrDrop {
+			if errors.Is(err, ErrDrop) {
 				return false, nil
 			} else {
 				return false, s.resetIPv4TCP(ipHdr, tcpHdr)
@@ -441,7 +442,7 @@ func (s *System) processIPv6TCP(ipHdr header.IPv6, tcpHdr header.TCP) (bool, err
 	} else {
 		natPort, err := s.tcpNat.Lookup(source, destination, s.handler)
 		if err != nil {
-			if err == ErrDrop {
+			if errors.Is(err, ErrDrop) {
 				return false, nil
 			} else {
 				return false, s.resetIPv6TCP(ipHdr, tcpHdr)
@@ -536,7 +537,7 @@ func (s *System) processIPv6UDP(ipHdr header.IPv6, udpHdr header.UDP) error {
 func (s *System) preparePacketConnection(source M.Socksaddr, destination M.Socksaddr, userData any) (bool, context.Context, N.PacketWriter, N.CloseHandlerFunc) {
 	pErr := s.handler.PrepareConnection(N.NetworkUDP, source, destination)
 	if pErr != nil {
-		if pErr != ErrDrop {
+		if !errors.Is(pErr, ErrDrop) {
 			if source.IsIPv4() {
 				ipHdr := userData.(header.IPv4)
 				s.rejectIPv4WithICMP(ipHdr, header.ICMPv4PortUnreachable)