Conn.Write should fail if Socket is destroyed

https://github.com/ipfs/go-ipfs/issues/2566

conn.go

@@ -337,7 +337,7 @@ func (c *Conn) deliveryProcessor() {
 
 func (c *Conn) lazyDestroy() {
 	if c.wroteFin && len(c.unackedSends) <= 1 && (c.gotFin || c.closed) {
-		c.destroy(nil)
+		c.destroy(errors.New("lazily destroyed"))
 	}
 }
 
@@ -550,8 +550,12 @@ func (c *Conn) Write(p []byte) (n int, err error) {
 	defer mu.Unlock()
 	for len(p) != 0 {
 		for {
-			if c.wroteFin || c.gotFin {
-				err = io.ErrClosedPipe
+			if c.wroteFin || c.closed {
+				err = errClosed
+				return
+			}
+			if c.destroyed {
+				err = c.err
 				return
 			}
 			if c.connDeadlines.write.deadlineExceeded() {

utp_test.go

@@ -571,3 +571,22 @@ func TestWriteClose(t *testing.T) {
 	require.EqualValues(t, "hiho", c)
 	b.Close()
 }
+
+func TestWriteUnderlyingPacketConnClosed(t *testing.T) {
+	// writeTimeout = time.Hour
+	// packetReadTimeout = time.Hour
+	pc, err := listenPacket("udp", "localhost:0")
+	require.NoError(t, err)
+	s, err := NewSocketFromPacketConn(pc)
+	require.NoError(t, err)
+	log.Println("pc closed")
+	dc, ac := connPairSocket(s)
+	defer dc.Close()
+	defer ac.Close()
+	pc.Close()
+	n, err := ac.Write([]byte("hello"))
+	require.Equal(t, 0, n)
+	require.EqualError(t, err, "error sending packet: closed")
+	_, err = dc.Read(nil)
+	require.EqualError(t, err, "Socket destroyed")
+}