device: receive: do not exit immediately on transient UDP receive errors

Some users report seeing lines like:

> Routine: receive incoming IPv4 - stopped

Popping up unexpectedly. Let's sleep and try again before failing, and
also log the error, and perhaps we'll eventually understand this
situation better in future versions.

Because we have to distinguish between the socket being closed
explicitly and whatever error this is, we bump the module to require Go
1.16.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

device/receive.go

@@ -8,6 +8,7 @@ package device
 import (
 	"bytes"
 	"encoding/binary"
+	"errors"
 	"net"
 	"strconv"
 	"sync"
@@ -17,6 +18,7 @@ import (
 	"golang.org/x/crypto/chacha20poly1305"
 	"golang.org/x/net/ipv4"
 	"golang.org/x/net/ipv6"
+
 	"golang.zx2c4.com/wireguard/conn"
 )
 
@@ -117,15 +119,13 @@ func (device *Device) RoutineReceiveIncoming(IP int, bind conn.Bind) {
 	buffer := device.GetMessageBuffer()
 
 	var (
-		err      error
-		size     int
-		endpoint conn.Endpoint
+		err         error
+		size        int
+		endpoint    conn.Endpoint
+		deathSpiral int
 	)
 
 	for {
-
-		// read next datagram
-
 		switch IP {
 		case ipv4.Version:
 			size, endpoint, err = bind.ReceiveIPv4(buffer[:])
@@ -137,8 +137,18 @@ func (device *Device) RoutineReceiveIncoming(IP int, bind conn.Bind) {
 
 		if err != nil {
 			device.PutMessageBuffer(buffer)
+			if errors.Is(err, net.ErrClosed) {
+				return
+			}
+			device.log.Error.Printf("Failed to receive packet: %v", err)
+			if deathSpiral < 10 {
+				deathSpiral++
+				time.Sleep(time.Second / 3)
+				continue
+			}
 			return
 		}
+		deathSpiral = 0
 
 		if size < MinMessageSize {
 			continue