whisper: fixed broadcast race

Whisper's expire and broadcast loops happen in two separate go routines.
Whenever an envelope is being expired it's removed from the set of
envelopes and it looses all information about the envelope, including
the "known hash". After the envelope has been removed it can be
re-accepted by a broadcasting peer putting back the envelope in the set
of envelopes. Since the envelope broadcast loop is separate of the
expire loop expired messages may be broadcast to other peer, resulting
in messages **never** being dropped.

This PR includes an expire check before adding new messages to the set
of envelopes.

whisper/peer_test.go

@@ -238,15 +238,18 @@ func TestPeerMessageExpiration(t *testing.T) {
 		t.Fatalf("failed to send message: %v", err)
 	}
 	payload := []interface{}{envelope}
+	if err := p2p.ExpectMsg(tester.stream, messagesCode, payload); err != nil {
+		// A premature empty message may have been broadcast, check the next too
 		if err := p2p.ExpectMsg(tester.stream, messagesCode, payload); err != nil {
 			t.Fatalf("message mismatch: %v", err)
 		}
+	}
 	// Check that the message is inside the cache
 	if !peer.known.Has(envelope.Hash()) {
 		t.Fatalf("message not found in cache")
 	}
 	// Discard messages until expiration and check cache again
-	exp := time.Now().Add(time.Second + expirationCycle)
+	exp := time.Now().Add(time.Second + 2*expirationCycle + 100*time.Millisecond)
 	for time.Now().Before(exp) {
 		if err := p2p.ExpectMsg(tester.stream, messagesCode, []interface{}{}); err != nil {
 			t.Fatalf("message mismatch: %v", err)

whisper/whisper.go

@@ -234,6 +234,11 @@ func (self *Whisper) add(envelope *Envelope) error {
 	self.poolMu.Lock()
 	defer self.poolMu.Unlock()
 
+	// short circuit when a received envelope has already expired
+	if envelope.Expiry <= uint32(time.Now().Unix()) {
+		return nil
+	}
+
 	// Insert the message into the tracked pool
 	hash := envelope.Hash()
 	if _, ok := self.messages[hash]; ok {

whisper/whisper_test.go

@@ -207,4 +207,13 @@ func TestMessageExpiration(t *testing.T) {
 	if found {
 		t.Fatalf("message not expired from cache")
 	}
+
+	node.add(envelope)
+	node.poolMu.RLock()
+	_, found = node.messages[envelope.Hash()]
+	node.poolMu.RUnlock()
+	if found {
+		t.Fatalf("message was added to cache")
+	}
+
 }