device: allow compiling with Go 1.15

Until we depend on Go 1.16 (which isn't released yet), alias our own
variable to the private member of the net package. This will allow an
easy find replace to make this go away when we eventually switch to
1.16.

Signed-off-by: Jason A. Donenfeld <[email protected]>

Author: zx2c4

Diff for: conn/conn_linux.go

@@ -204,7 +204,7 @@ func (bind *nativeBind) ReceiveIPv6(buff []byte) (int, Endpoint, error) {
 
 	var end NativeEndpoint
 	if bind.sock6 == -1 {
-		return 0, nil, net.ErrClosed
+		return 0, nil, NetErrClosed
 	}
 	n, err := receive6(
 		bind.sock6,
@@ -220,7 +220,7 @@ func (bind *nativeBind) ReceiveIPv4(buff []byte) (int, Endpoint, error) {
 
 	var end NativeEndpoint
 	if bind.sock4 == -1 {
-		return 0, nil, net.ErrClosed
+		return 0, nil, NetErrClosed
 	}
 	n, err := receive4(
 		bind.sock4,
@@ -237,12 +237,12 @@ func (bind *nativeBind) Send(buff []byte, end Endpoint) error {
 	nend := end.(*NativeEndpoint)
 	if !nend.isV6 {
 		if bind.sock4 == -1 {
-			return net.ErrClosed
+			return NetErrClosed
 		}
 		return send4(bind.sock4, nend, buff)
 	} else {
 		if bind.sock6 == -1 {
-			return net.ErrClosed
+			return NetErrClosed
 		}
 		return send6(bind.sock6, nend, buff)
 	}

Diff for: conn/net_err_closed.go

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2021 WireGuard LLC. All Rights Reserved.
+ */
+
+package conn
+
+import _ "unsafe"
+
+//TODO: replace this with net.ErrClosed for Go 1.16
+
+//go:linkname NetErrClosed internal/poll.ErrNetClosing
+var NetErrClosed error

Diff for: device/receive.go

@@ -112,7 +112,7 @@ func (device *Device) RoutineReceiveIncoming(IP int, bind conn.Bind) {
 
 		if err != nil {
 			device.PutMessageBuffer(buffer)
-			if errors.Is(err, net.ErrClosed) {
+			if errors.Is(err, conn.NetErrClosed) {
 				return
 			}
 			device.log.Error.Printf("Failed to receive packet: %v", err)

Diff for: go.mod

@@ -1,6 +1,6 @@
 module golang.zx2c4.com/wireguard
 
-go 1.16
+go 1.15
 
 require (
 	golang.org/x/crypto v0.0.0-20201221181555-eec23a3978ad