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Add fork version to topic 

Gossipsub peers are separate from the ETH2 RPC protocol, and thus cannot
rely on the application-level `Status` negotiation to establish if
they're on the same network.

Segregating gossipsub topics by fork version decouples RPC from gossip
further and allows peers to more easily listen only to the traffic of
the network they're interested in, without further negotiation.
This commit is contained in:
Jacek Sieka 2020-02-17 10:03:32 +01:00
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commit 52b45ab9de
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14
specs/phase0/p2p-interface.md
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@ -216,7 +216,17 @@ The following gossipsub [parameters](https://github.com/libp2p/specs/tree/master
### Topics and messages
Topics are plain UTF-8 strings and are encoded on the wire as determined by protobuf (gossipsub messages are enveloped in protobuf messages). Topic strings have form: `/eth2/TopicName/TopicEncoding`. This defines both the type of data being sent on the topic and how the data field of the message is encoded.
Topics are plain UTF-8 strings and are encoded on the wire as determined by protobuf (gossipsub messages are enveloped in protobuf messages). Topic strings have form: `/eth2/ForkVersion/Name/Encoding`. This defines both the type of data being sent on the topic and how the data field of the message is encoded.
- `ForkVersion` - the hex-encoded bytes from `state.fork.current_version` of the head state of the client, as also seen in `Status.head_fork_version`.
- `Name` - see table below
- `Encoding` - the encoding strategy describes a specific representation of bytes that will be transmitted over the wire. See the [Encodings](#Encoding-strategies) section for further details.
The fork version is hex-encoded using the following scheme:
```python
ForkVersion = ''.join('{:02x}'.format(x) for x in state.fork.current_version)
```
For example, the fork version `[0, 1, 2, 10]` will be encoded as `0001020a`.
Each gossipsub [message](https://github.com/libp2p/go-libp2p-pubsub/blob/master/pb/rpc.proto#L17-L24) has a maximum size of `GOSSIP_MAX_SIZE`. Clients MUST reject (fail validation) messages that are over this size limit. Likewise, clients MUST NOT emit or propagate messages larger than this limit.
@ -229,7 +239,7 @@ where `base64` is the [URL-safe base64 alphabet](https://tools.ietf.org/html/rfc
The payload is carried in the `data` field of a gossipsub message, and varies depending on the topic:
| Topic | Message Type |
| Name | Message Type |
|------------------------------------------------|-------------------------|
| beacon_block | SignedBeaconBlock |
| beacon_aggregate_and_proof | SignedAggregateAndProof |