feat: Add raw spec for /gossipsub-relay/1.0.0 protocol

vac/raw/gossipsub-relay.md

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+---
+title: GOSSIPSUB-RELAY
+name: GossipSub Relay Protocol
+status: raw
+editor: Akshaya Mani <akshaya@status.im>
+contributors: Richard Ramos <richard@status.im>, Daniel Kaiser <danielkaiser@status.im>
+---
+
+**Protocol identifier**: `/gossipsub-relay/1.0.0`
+
+## Motivation and Goals
+
+The Gossipsub Relay Protocol defines a minimal request/response interface
+that allows external clients to inject pre-constructed GossipSub messages
+into the relay logic of a full GossipSub node, without requiring mesh
+participation or GossipSub protocol support.
+
+This enables lightweight or stateless clients and anonymity systems&mdash;such as
+mixnets&mdash;to send messages into the GossipSub network without joining the mesh,
+maintaining long-lived streams, or managing peer scoring.
+
+## Use Case: Mixnet Integration
+
+A motivating use case is the Mix Protocol, where a sender anonymously routes a
+message through a mix network composed of participating libp2p nodes. The final
+hop on the mix network (*i.e.,* the exit node) forwards the message to the
+Gossipsub Relay Protocol at the destination node.
+
+The Relay handler receives the message as a raw byte stream and passes it to
+the handler of the local Gossipsub instance, which then processes and
+disseminates the message as if it arrived from a regular mesh peer.
+
+This design cleanly separates the anonymous routing layer, offered by Mix,
+from the GossipSub relay logic.
+
+## Protocol Overview
+
+`/gossipsub-relay/1.0.0` is a unary request/response protocol where:
+
+- The client sends a single request containing a serialized `RPC` protobuf
+  message, as defined by the
+  [Gossipsub specification](https://github.com/libp2p/specs/tree/master/pubsub/gossipsub).
+- The server passes this byte sequence directly the handler of the local
+  GossipSub instance, without attempting to parse or interpret it.
+- The server responds with a simple acknowledgment&mdash;`success` or `error`&mdash;
+  and closes the stream.
+
+The server node MUST run both the GossipSub and GossipSub Relay protocols. The
+Relay Protocol is agnostic to the structure of the payload. It serves only as
+an interface between the client and the local GossipSub logic.
+
+Unlike `Waku Lightpush`, this protocol **does not** trigger a publish
+operation directly. Instead, it defers all processing and relaying to the
+local Gossipsub instance.
+
+## Protobuf
+
+The relay protocol uses a simple wrapper message for binary payload injection:
+
+```protobuf
+  syntax = "proto3";
+
+  message Request {
+    // Opaque byte sequence representing a serialized GossipSub RPC message.
+    bytes data = 1;
+  }
+
+  message Response {
+    // Indicates success or failure of message injection
+    bool is_success = 1;
+
+    // Optional error or status message
+    string info = 2;
+  }
+```
+
+## Protocol Requirements
+
+libp2p nodes implementing `/gossipsub-relay/1.0.0` MUST:
+
+- Run a full local GossipSub instance.
+- Accept incoming streams using `/gossipsub-relay/1.0.0`.
+- On receiving a `Request`, treat the data field as an opaque byte sequence.
+- Invoke the local GossipSub handler with the `data`. The local GossipSub
+  instance then validates and relays the `data` as if it was received from a
+  mesh peer.
+- Respond with a `Response` indicating whether the injection succeeded.
+
+Clients may open a new stream for subsequent requests.
+
+The relay protocol itself MUST NOT inspect or parse the payload. The local
+GossipSub handler is responsible for parsing the received bytes and validating
+that it conforms to a valid `RPC` message as defined by the Gossipsub spec.
+
+## Security Considerations
+
+This protocol enables arbitrary clients to inject raw payloads into the local
+GossipSub handler without performing origin authentication or message
+integrity checks.
+
+Implementers SHOULD take steps to mitigate abuse, such as:
+
+- Enforce per-IP or per-peer rate limits.
+- Reject oversized payloads.
+
+The relay node itself SHOULD remain stateless with respect to injected
+messages.
+
+## Compatibility
+
+This protocol is transport-agnostic and can be mounted alongside other
+Gossipsub-compatible protocols. It does not require any changes to the core
+Gossipsub specification.
+
+To receive messages via this protocol, a node MUST also mount the GossipSub protocol.
+
+## Copyright
+
+Copyright and related rights waived via
+[CC0](https://creativecommons.org/publicdomain/zero/1.0/).
+
+## References
+
+- [libp2p Gossipsub specification](https://github.com/libp2p/specs/tree/master/pubsub/gossipsub)