Merge pull request whiteblock#45 from atoulme/patch-3

Add gossip spec

Author: dreamcodez

gossip.md

@@ -0,0 +1,62 @@
+# Messages
+These messages are used to define a gossip protocol for Ethereum 2.0. These messages define a gossip protocol for clients to replicate information with each other.
+
+# Envelope
+All messages follow the envelope standard to Hobbits as described in [protocol.md].
+
+This application protocol is classified under the `GOSSIP` command.
+
+The message must contain the following headers:
+
+| Header name | Type | Notes |
+|-------------|------|-------|
+| method_id   | uint8| the method used in this exchange, as described below |
+| message_hash | bytes32 | a hash uniquely representing the message contents, with a hash function up to the application |
+| hash_signature | bytes32 | a signature of the message hash with a public key identifying the node sending data |
+
+Example (showing the bson snappy data as json):
+
+```python
+EWP 0.2 GOSSIP 24 0
+{
+  "method_id": 3,
+  "message_hash": "0x9D686F6262697473206172652074776F20616E6420666F75722066656574",
+  "hash_signature": "0x0000000009A4672656E63682070656F706C6520617265207468652062657374"
+}
+```
+
+# Methods
+
+## 0x00 GOSSIP
+
+Nodes use `GOSSIP` methods to send data to other nodes in the network.
+
+The body of a `GOSSIP` method consists in the data being gossiped.
+
+The `message_hash` header value must match the hash of the contents of the body according to a predefined hash function defined by the application.
+
+## 0x01 PRUNE
+
+Nodes use `PRUNE` messages to inform other nodes that they are removed from the list of peers that will receive data from them.
+Instead of sending data, nodes will send attestations as `IHAVE` messages.
+
+The header may contain the `message_hash` of a message that triggered the pruning.
+
+## 0x02 GRAFT
+
+Nodes use `PRUNE` messages to inform other nodes that they are added to the list of peers that will receive data from them.
+Instead of sending attestations as `IHAVE` messages, nodes will send data as `GOSSIP` messages.
+
+No body is present in `GRAFT` messages.
+
+The header may contain the `message_hash` of a message triggered the graft.
+
+Targets should reply with a `GOSSIP` message sending the message matching the hash.
+
+## 0x03 IHAVE
+
+Nodes use `IHAVE` messages to inform other nodes that they are in possession of data that matches the signature they are sending.
+
+No body is present in `IHAVE` messages.
+
+The header must contain the `message_hash` with the value of the hash of the data attested by the peer.