[GossipSub 1.2] IDONTWANT control message (#548)

* Add draft DONTSEND Gossip control message spec

* Rename DONTSEND to IDONTWANT

* Use the proper SHOULD and MAY wordings

* gossipsub v1.2 scaffolding

* Add authors and interest group members

* Remove potential use cases which may potentially lead to amplification

* Minor rephrasing with MAY/SHOULD

* Change SHOULD to MUST according to discussion in comments

* Make the ControlIDontWant.messageIDs plural to be consistent with IHAVE and IWANT messages

Co-authored-by: Pop Chunhapanya <haxx.pop@gmail.com>

* Change filed name to lower case for consistency with original spec

Co-authored-by: João Oliveira <hello@jxs.pt>

---------

Co-authored-by: vyzo <vyzo@hackzen.org>
Co-authored-by: Pop Chunhapanya <haxx.pop@gmail.com>
Co-authored-by: João Oliveira <hello@jxs.pt>

pubsub/gossipsub/gossipsub-v1.2.md

@@ -0,0 +1,106 @@
+# gossipsub v1.2: TODO
+
+| Lifecycle Stage | Maturity                  | Status | Latest Revision |
+|-----------------|---------------------------|--------|-----------------|
+| 1A              | Working Draft             | Active | r1, 2023-07-14  |
+
+Authors: [@Nashatyrev], [@Menduist]
+
+Interest Group: [@vyzo], [@Nashatyrev], [@Menduist]
+
+[@vyzo]: https://github.com/vyzo
+[@Nashatyrev]: https://github.com/Nashatyrev
+[@Menduist]: https://github.com/Menduist
+
+See the [lifecycle document][lifecycle-spec] for context about maturity level and spec status.
+
+[lifecycle-spec]: https://github.com/libp2p/specs/blob/master/00-framework-01-spec-lifecycle.md
+
+# Overview
+
+This document aims to provide a minimal extension to the [gossipsub
+v1.1](https://github.com/libp2p/specs/blob/master/pubsub/gossipsub/gossipsub-v1.1.md)
+protocol.
+
+The proposed extensions are backwards-compatible and aim to enhance the
+efficiency (minimize amplification/duplicates and decrease message latency) of
+the gossip mesh networks for larger messages. 
+
+In more specific terms, a new control message is introduced: `IDONTWANT`. It's primarily 
+intended to notify mesh peers that the node already received a message and there is no 
+need to send its duplicate.
+
+# Specification
+
+## Protocol Id
+
+Nodes that support this Gossipsub extension should additionally advertise the
+version number `1.2.0`. Gossipsub nodes can advertise their own protocol-id
+prefix, by default this is `meshsub` giving the default protocol id:
+- `/meshsub/1.2.0`
+
+## Parameters
+
+This section lists the configuration parameters that needs to agreed on across clients to avoid 
+ peer penalizations
+
+| Parameter                | Description                                                      | Reasonable Default |
+|--------------------------|------------------------------------------------------------------|--------------|
+| `max_idontwant_messages` | The maximum number of `IDONTWANT` messages per heartbeat per peer | ???  |
+
+
+## IDONTWANT Message
+
+### Basic scenario
+
+When the peer receives the first message instance it immediately broadcasts 
+(not queue for later piggybacking) `IDONTWANT` with the `messageId` to all its mesh peers. 
+This could be performed prior to the message validation to further increase the effectiveness of the approach.    
+
+On the other side a node maintains per-peer `dont_send_message_ids` set. Upon receiving `IDONTWANT` from 
+a peer the `messageId` is added to the `dont_send_message_ids` set. 
+When later relaying the `messageId` message to the mesh the peers found in `dont_send_message_ids` MUST be skipped. 
+
+Old entries from `dont_send_message_ids` SHOULD be pruned during heartbeat processing. 
+The prune strategy is outside of the spec scope and can be decided by implementations.
+
+`IDONTWANT` message is supposed to be _optional_ for both receiver and sender. I.e. the sender MAY NOT utilize 
+this message. The receiver in turn MAY ignore `IDONTWANT`: sending a message after the corresponding `IDONTWANT` 
+should not be penalized.    
+
+The `IDONTWANT` may have negative effect on small messages as it may increase the overall traffic and CPU load.
+Thus it is better to utilize `IDONTWANT` for messages of a larger size.
+The exact policy of `IDONTWANT` appliance is outside of the spec scope. Every implementation MAY choose whatever 
+is more appropriate for it. Possible options are either choose a message size threshold and broadcast `IDONTWANT`
+on per message basis when the size is exceeded or just use `IDONTWANT` for all messages on selected topics.
+
+To prevent DoS the number of `IDONTWANT` control messages is limited to `max_idontwant_messages` per heartbeat  
+
+### Cancelling `IWANT`
+
+If a node requested a message via `IWANT` and then occasionally receives the message from other peer it MAY 
+try to cancel its `IWANT` requests with the corresponding `IDONTWANT` message. It may work in cases when a
+peer delays/queues `IWANT` requests and the `IWANT` request SHOULD be removed from the queue if not processed yet
+
+## Protobuf Extension
+
+The protobuf messages are identical to those specified in the [gossipsub v1.0.0
+specification](https://github.com/libp2p/specs/blob/master/pubsub/gossipsub/gossipsub-v1.0.md)
+with the following  control message modifications:
+
+```protobuf
+message RPC {
+ // ... see definition in the gossipsub specification
+}
+
+message ControlMessage {
+    // messages from v1.0
+    repeated ControlIDontWant idontwant = 5;
+}
+
+message ControlIDontWant {
+    repeated bytes messageIDs = 1;
+}
+
+```
+