fix: use net.ErrClosed

fixes: #19

internal/networking/native/go-udpconn.go

@@ -2,11 +2,11 @@ package native
 
 import (
 	"context"
+	"errors"
 	"net"
 	"time"
 
 	"github.com/fastcat/wirelink/internal/networking"
-	"github.com/fastcat/wirelink/util"
 )
 
 // GoUDPConn implements networking.UDPConn by wrapping net.UDPConn
@@ -69,7 +69,7 @@ READLOOP:
 			now := time.Now()
 
 			if err != nil {
-				if util.IsNetClosing(err) {
+				if errors.Is(err, net.ErrClosed) {
 					// the socket has been closed, we're done
 					break READLOOP
 				}

internal/networking/vnet/socket-udpconn.go

@@ -85,7 +85,7 @@ func (sc *socketUDPConn) ReadFromUDP(b []byte) (n int, addr *net.UDPAddr, err er
 	inbound := sc.inbound
 	sc.s.m.Unlock()
 	if inbound == nil {
-		err = errors.New(util.NetClosingErrorString)
+		err = net.ErrClosed
 		return
 	}
 	p := <-sc.inbound

util/net.go

@@ -4,25 +4,8 @@ import (
 	"net"
 	"sort"
 	"strings"
-
-	"github.com/pkg/errors"
 )
 
-// NetClosingErrorString is the voodoo string returned when you try to use a
-// Close()d network connection, because https://github.com/golang/go/issues/4373
-const NetClosingErrorString = "use of closed network connection"
-
-// IsNetClosing checks err and its Unwrap chain for NetClosingErrorString
-func IsNetClosing(err error) bool {
-	if err == nil {
-		return false
-	}
-	if strings.Contains(err.Error(), NetClosingErrorString) {
-		return true
-	}
-	return IsNetClosing(errors.Unwrap(err))
-}
-
 // UDPEqualIPPort checks if to UDPAddrs are equal in terms of their IP and Port
 // fields, but ignoring any Zone value
 func UDPEqualIPPort(a, b *net.UDPAddr) bool {