[I] Serve the legacy SDK gRPC protocol on the v2 runtime (port 10205 compatibility bridge) (eventmesh)

["qqeasonchen (via GitHub)" <gi...@apache.org>]

qqeasonchen opened a new issue, #5411:
URL: https://github.com/apache/eventmesh/issues/5411

   ## Motivation
   
   The v2 runtime serves HTTP + CloudEvents on 10105/10106 (WS 10107, A2A 10108) and keeps `eventmesh.grpc.port=10205` **RESERVED** (configuration.md: "not served yet; keeps the 1.x default warm"). Meanwhile the legacy SDK surface is fully preserved on develop:
   
   - `eventmesh-sdks/eventmesh-sdk-java` ships complete gRPC clients — `EventMeshGrpcProducer` / `EventMeshGrpcConsumer` (blocking + async stubs) targeting `PublisherService` / `ConsumerService` / `HeartbeatService` / `RegistryService` (`org.apache.eventmesh.cloudevents.v1.*`)
   - The generated protocol classes live in `eventmesh-common` (`org.apache.eventmesh.common.protocol.grpc.*`), so no proto regeneration is needed
   - Go / Rust SDKs keep their gRPC protos too
   
   Per the capability table these SDKs are **Legacy-compatible: "kept so old clients run unmodified"** — but today an old gRPC client has nothing to connect to: the contract is broken. README/protocols.md advertise legacy gRPC compatibility; the runtime should honor it.
   
   ## Proposal
   
   Serve the legacy gRPC protocol on the reserved port 10205 as a **compatibility bridge** onto the v2 ingress path (no second messaging engine):
   
   1. **`EventMeshGrpcServer`** (new, `eventmesh-runtime/.../grpc/`): gRPC `ServerBuilder` on `eventmesh.grpc.port` (default 10205, `0` = disabled — opt-in like the WS port), graceful shutdown with the app lifecycle.
   2. **Publisher bridge**: `publish` / `batchPublish` / `requestReply` — map the proto `CloudEvent` (attributes via `EventMeshCloudEventUtils`) to a v2 `io.cloudevents.CloudEvent` and hand it to `UniIngressService.publish` (WAL durability, at-least-once — same semantics as the HTTP path). `requestReply` maps onto the existing request/reply correlation. Reply: legacy `Response` codes in `StatusCode`.
   3. **Consumer bridge**: `register`/`subscribe`/`unsubscribe` map onto the v2 subscription registry (clientId derived from `consumerGroup`+`env`+`idc` headers; `url` webhook style and the SDK's own client-callback are bridged to long-poll internally). `subscribeStream` (bidi) is served by pumping the v2 push pipeline into the stream — same dispatcher the SSE path uses.
   4. **Heartbeat / Registry**: in-memory registrations with the same TTL model the agent plane uses; heartbeats refresh, reaper evicts stale gRPC clients.
   5. **Group semantics**: legacy `consumerGroup` maps to a v2 subscription group with `LOAD_BALANCE` mode (SDK default `CLUSTERING`), URL-subscriptions to `BROADCAST` where the old protocol used broadcasting — documented in a compatibility table.
   6. **Docs**: protocols.md legacy-gRPC section + configuration.md flips the 10205 row from RESERVED to served (opt-in); README capability-table row unchanged (still Legacy-compatible) but the Recommendation note gains "gRPC bridge served since #<this PR>".
   7. **Tests**: hermetic unit tests for the proto↔v2 CloudEvent mapping; an integration test booting the gRPC server against the in-memory storage and driving it with the **existing** `EventMeshGrpcProducer`/`EventMeshGrpcConsumer` (the SDK is its own conformance suite).
   
   ### Non-goals (follow-ups)
   
   - New (non-legacy) gRPC-native v2 API — HTTP + CloudEvents stays the primary path
   - gRPC admin surface (the `AdminService` proto stays unimplemented, as on 1.x)
   - Go/Rust SDK verification against the bridge (Java SDK first; the protos are shared so others should follow, tracked separately)
   
   ## Compatibility risk
   
   Low: the bridge is opt-in (`eventmesh.grpc.port` unset = off), touches no existing path, and reuses the v2 delivery engine, so offset/ACK/retry semantics cannot diverge.
   


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Re: [I] Serve the legacy SDK gRPC protocol on the v2 runtime (port 10205 compatibility bridge) (eventmesh)

["qqeasonchen (via GitHub)" <gi...@apache.org>]

qqeasonchen closed issue #5411: Serve the legacy SDK gRPC protocol on the v2 runtime (port 10205 compatibility bridge)
URL: https://github.com/apache/eventmesh/issues/5411


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