Exercise address reuse across a wrap and send from an ephemeral port in the proxy test

client/iface/wgproxy/loopback/addr_test.go

@@ -47,29 +47,38 @@ func TestAllocatorSkipsNetworkAndBroadcastHosts(t *testing.T) {
 func TestAllocatorReusesReleasedAddresses(t *testing.T) {
 	var a allocator
 	taken := make(map[netip.Addr]bool)
-
-	first, err := a.next(func(candidate netip.Addr) bool { return taken[candidate] })
-	if err != nil {
-		t.Fatalf("allocate: %v", err)
-	}
-	taken[first] = true
-
-	// release it and allocate until the cursor wraps back around to it
-	delete(taken, first)
-	for i := 0; i < 10; i++ {
-		addr, err := a.next(func(candidate netip.Addr) bool { return taken[candidate] })
+	inUse := func(candidate netip.Addr) bool { return taken[candidate] }
+	alloc := func() netip.Addr {
+		t.Helper()
+		addr, err := a.next(inUse)
 		if err != nil {
-			t.Fatalf("allocate %d: %v", i, err)
-		}
-		if addr == first {
-			return
+			t.Fatalf("allocate: %v", err)
 		}
 		taken[addr] = true
+		return addr
 	}
-	// the cursor moves forward, so reuse only happens after a full wrap. Assert
-	// the released address is at least still considered free.
-	if inUse := taken[first]; inUse {
-		t.Fatalf("released address %s still marked in use", first)
+
+	first := alloc()
+	second := alloc()
+	delete(taken, first)
+
+	// The cursor only moves forward, so a released address comes back after a
+	// wrap. Park the cursor near the end of the range instead of allocating
+	// 2^23 addresses: the next call takes the last usable address, and the one
+	// after that wraps past the skipped .255 and .0 hosts to the released one.
+	a.cursor = addrRangeSize - 3
+	last := alloc()
+	if want := netip.MustParseAddr("127.255.255.254"); last != want {
+		t.Fatalf("expected the last usable address %s before the wrap, got %s", want, last)
+	}
+
+	if reused := alloc(); reused != first {
+		t.Fatalf("expected the released address %s after the wrap, got %s", first, reused)
+	}
+
+	// second is still held, so the allocator must step over it.
+	if next := alloc(); next == second {
+		t.Fatalf("allocator handed out %s while it was still in use", second)
 	}
 }
 

client/iface/wgproxy/loopback/proxy_privileged_test.go

@@ -79,7 +79,7 @@ func TestProxyDemuxesByDestinationAddress(t *testing.T) {
 		seen[endpoint.IP.String()] = true
 	}
 
-	wgSock, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: testWGPort})
+	wgSock, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.ParseIP("127.0.0.1")})
 	if err != nil {
 		t.Fatalf("wg socket: %v", err)
 	}