Filter gossipsub message duplication (#736)

* Add duplication prevention to gossipsub

* Clean up topic logs

* Add content addressed messages for gossip

beacon_node/eth2-libp2p/src/topics.rs

@@ -0,0 +1,71 @@
+use libp2p::gossipsub::Topic;
+use serde_derive::{Deserialize, Serialize};
+
+/// The gossipsub topic names.
+// These constants form a topic name of the form /TOPIC_PREFIX/TOPIC/ENCODING_POSTFIX
+// For example /eth2/beacon_block/ssz
+pub const TOPIC_PREFIX: &str = "eth2";
+pub const TOPIC_ENCODING_POSTFIX: &str = "ssz";
+pub const BEACON_BLOCK_TOPIC: &str = "beacon_block";
+pub const BEACON_ATTESTATION_TOPIC: &str = "beacon_attestation";
+pub const VOLUNTARY_EXIT_TOPIC: &str = "voluntary_exit";
+pub const PROPOSER_SLASHING_TOPIC: &str = "proposer_slashing";
+pub const ATTESTER_SLASHING_TOPIC: &str = "attester_slashing";
+pub const SHARD_TOPIC_PREFIX: &str = "shard";
+
+/// Enum that brings these topics into the rust type system.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub enum GossipTopic {
+    BeaconBlock,
+    BeaconAttestation,
+    VoluntaryExit,
+    ProposerSlashing,
+    AttesterSlashing,
+    Shard,
+    Unknown(String),
+}
+
+impl From<&str> for GossipTopic {
+    fn from(topic: &str) -> GossipTopic {
+        let topic_parts: Vec<&str> = topic.split('/').collect();
+        if topic_parts.len() == 4
+            && topic_parts[1] == TOPIC_PREFIX
+            && topic_parts[3] == TOPIC_ENCODING_POSTFIX
+        {
+            match topic_parts[2] {
+                BEACON_BLOCK_TOPIC => GossipTopic::BeaconBlock,
+                BEACON_ATTESTATION_TOPIC => GossipTopic::BeaconAttestation,
+                VOLUNTARY_EXIT_TOPIC => GossipTopic::VoluntaryExit,
+                PROPOSER_SLASHING_TOPIC => GossipTopic::ProposerSlashing,
+                ATTESTER_SLASHING_TOPIC => GossipTopic::AttesterSlashing,
+                unknown_topic => GossipTopic::Unknown(unknown_topic.into()),
+            }
+        } else {
+            GossipTopic::Unknown(topic.into())
+        }
+    }
+}
+
+impl Into<Topic> for GossipTopic {
+    fn into(self) -> Topic {
+        Topic::new(self.into())
+    }
+}
+
+impl Into<String> for GossipTopic {
+    fn into(self) -> String {
+        match self {
+            GossipTopic::BeaconBlock => topic_builder(BEACON_BLOCK_TOPIC),
+            GossipTopic::BeaconAttestation => topic_builder(BEACON_ATTESTATION_TOPIC),
+            GossipTopic::VoluntaryExit => topic_builder(VOLUNTARY_EXIT_TOPIC),
+            GossipTopic::ProposerSlashing => topic_builder(PROPOSER_SLASHING_TOPIC),
+            GossipTopic::AttesterSlashing => topic_builder(ATTESTER_SLASHING_TOPIC),
+            GossipTopic::Shard => topic_builder(SHARD_TOPIC_PREFIX),
+            GossipTopic::Unknown(topic) => topic,
+        }
+    }
+}
+
+fn topic_builder(topic: &'static str) -> String {
+    format!("/{}/{}/{}", TOPIC_PREFIX, topic, TOPIC_ENCODING_POSTFIX,)
+}