all: use TCP instead of UDP

README.md

@@ -69,11 +69,9 @@ Packet type (1 byte) <br>
 
 
 ## Transport/Security layer
-Transport layer supports peer-to-peer UDP communication.
+Transport layer supports peer-to-peer TCP communication. UDP is sufficient If the communication is simply sending a PullRequest to a random peer. However, this library's PullResponse payload size is unpredictable and will likely exceed the safe from packet fragmentation UDP size of 508 bytes(The minimum size of IPv4 datagram every device has to be able to receive(i.g. MTU) is 576 byte. And IP header(with fully option field) is 60 byte, UDP header is 8 byte. So I guess safety maximum UDP packet size from packet fragmentation is 508(576 - 60 - 8) byte). Implementing with UDP requires chopping packets at the application level and sending them over UDP to avoid packet fragmentation. There's no basis for doing that. <br>
 Security layer resolve the secure between peer to peer trnasmission. It should be possible to add multiple encryption algorithms. I'm just considering a method of encrypting and decrypting using a passphrase(It is also okay to encrypt in the application and then propagate it. In this case, you should set NO-SECURE in config). <br>
 
 Encrypt alogrithm (1 byte) <br>
 > 0: NO-SECURE <br>
 > 1: AES-256-CBC <br>
-
-Max packet size is n.

gossip.go

@@ -125,13 +125,27 @@ func (g *Gossiper) selectRandomPeers(n int) []string {
 	if len(peers) <= n {
 		return peers
 	}
-	random := rand.New(rand.NewSource(time.Now().UnixNano()))
 
-	// TODO(dbadoy): Avoid duplicate selection.
-	selected := make([]string, 0, n)
+	var (
+		random   = rand.New(rand.NewSource(time.Now().UnixNano()))
+		indices  = make([]int, 0, n)
+		selected = make([]string, 0, n)
+	)
+
+	// Avoid duplicate selection.
+	for r := random.Intn(n); len(indices) != n; r = random.Intn(n) {
+		for _, v := range indices {
+			if v == r {
+				continue
+			}
+		}
+		indices = append(indices, r)
+	}
+
 	for i := 0; i < n; i++ {
-		selected = append(selected, peers[random.Intn(n)])
+		selected = append(selected, peers[indices[i]])
 	}
+
 	return selected
 }
 

handler.go

@@ -38,6 +38,9 @@ func (g *Gossiper) pullRequestHandle(payload []byte, sender *net.UDPAddr) []Pack
 	if len(kl) != len(vl) {
 		panic("pullRequestHandle: invalid protocol detected, different key value sizes in the packet")
 	}
+	if len(kl) == 0 {
+		return nil
+	}
 
 	var packets []Packet