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scrabble-game/gateway/README.md
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Stage 12: observability & performance (OTel/OTLP, domain metrics, guest GC)
- pkg/telemetry: shared OTel provider bootstrap (none/stdout/otlp + W3C
  propagators + Go runtime metrics); backend/internal/telemetry becomes a thin
  facade keeping its gin middleware.
- Telemetry parity: gateway and the Telegram connector gain telemetry runtimes
  and config (GATEWAY_/TELEGRAM_ SERVICE_NAME + OTEL_*); otelgrpc instruments the
  backend push server, the gateway's backend+connector clients and the connector
  server. Default exporter stays none (collector/dashboards are Stage 14).
- Operational metrics (variant attribute on game-scoped ones): game_replay_duration,
  game_move_validate_duration, games_started_total, games_abandoned_total,
  game_cache_active, chat_messages_total{kind}, gateway edge_request_duration.
  Wired via the SetMetrics setter pattern (default no-op meter).
- TODO-3: account.GuestReaper deletes guests with no game seat past
  BACKEND_GUEST_RETENTION (default 30d, swept every BACKEND_GUEST_REAP_INTERVAL).
- Tests: pkg/telemetry exporter selection; game/social/edge metric recording via
  a manual reader; config (otlp accepted, guest knobs); inttest guest reaper.
- Docs: PLAN.md re-scopes Stage 12 and adds Stage 13 (alphabet-on-wire) + Stage 14
  (CI/deploy) with the agreed dictionary-versioning resolution; ARCHITECTURE 11/13,
  TESTING, the three READMEs and FUNCTIONAL(+ru) updated.
2026-06-04 14:22:15 +02:00

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# gateway
The Scrabble platform's only public ingress (module `scrabble/gateway`). It
terminates the client's **Connect-RPC + FlatBuffers** traffic over HTTP/2
cleartext (`h2c`), authenticates the originating credential, mints/resolves a
thin opaque session, rate-limits, injects `X-User-ID` when forwarding to the
backend over REST/JSON, and bridges the backend's gRPC push stream to each
client's in-app live channel. It also serves the backend's admin console at `/_gm`
on its public listener behind HTTP Basic-Auth. See
[`../docs/ARCHITECTURE.md`](../docs/ARCHITECTURE.md) §2, §3, §10, §12.
## Package layout
```
cmd/gateway/ # main: config -> backend client -> session cache ->
# push hub -> Connect h2c server (+ admin) -> serve
proto/edge/v1/ # Connect envelope contract (committed generated Go)
internal/config/ # GATEWAY_* env config
internal/backendclient/ # typed REST client (+ X-User-ID) and push gRPC client
internal/session/ # in-memory session cache (LRU/TTL, backend fallback)
internal/ratelimit/ # token-bucket limiter (golang.org/x/time/rate)
internal/connector/ # gRPC client to the Telegram connector (initData validate, out-of-app push) + routing
internal/push/ # live-event fan-out hub (per-user client streams)
internal/transcode/ # FlatBuffers<->REST bridge + message_type registry
internal/connectsrv/ # the Connect Gateway service over h2c
internal/admin/ # Basic-Auth reverse proxy mounting the backend admin console at /_gm (verbatim)
```
The FlatBuffers payloads and the backend push proto are the shared wire
contracts in [`../pkg`](../pkg).
## Transport contract
A single `Gateway` Connect service: `Execute(message_type, payload, request_id)`
for unary operations and `Subscribe` for the live stream. The `payload` bytes are
FlatBuffers tables (`scrabble/pkg/fbs`); the gateway transcodes them to and from
the backend's JSON. The session token rides in `Authorization: Bearer`; `auth.*`
operations are unauthenticated and return the minted token. A unary domain
outcome rides back in `ExecuteResponse.result_code` (HTTP 200); only edge
failures become Connect error codes.
`auth.telegram` validates the Mini App `initData` by calling the **Telegram connector**
(`GATEWAY_CONNECTOR_ADDR`), which holds the bot token; the gateway also routes
out-of-app push to that connector for recipients with no live in-app stream
(ARCHITECTURE.md §10). When `GATEWAY_CONNECTOR_ADDR` is unset, both are disabled.
The Stage 6 message-type slice: `auth.telegram`, `auth.guest`,
`auth.email.request`, `auth.email.login`, `profile.get`, `game.submit_play`,
`game.state`, `lobby.enqueue`, `lobby.poll`, `chat.post`; live events
`your_turn`, `opponent_moved`, `chat_message`, `nudge`, `match_found`. Stage 7
added the play-loop ops; **Stage 8** added the social/account/history ops —
`friends.*` (list/incoming/request/respond/cancel/unfriend/code.issue/code.redeem),
`blocks.*`, `invitation.*` (list/create/accept/decline/cancel), `profile.update`,
`stats.get`, `game.gcg`, and the `notify` live event — all via the identical
transcode pattern (`transcode_social.go`). **Stage 11** added account linking & merge
`link.email.request/confirm/merge` and `link.telegram.confirm/merge`
(`transcode_link.go`); the telegram ops validate the **Login Widget** payload via the
connector (`ValidateLoginWidget`) and forward the trusted `external_id`. These
**superseded** the Stage 8 `email.bind.*` ops, which were removed.
## Configuration
| Variable | Default | Notes |
| --- | --- | --- |
| `GATEWAY_HTTP_ADDR` | `:8081` | public Connect/h2c listener (also serves the admin console at `/_gm`) |
| `GATEWAY_LOG_LEVEL` | `info` | zap level |
| `GATEWAY_BACKEND_HTTP_URL` | `http://localhost:8080` | backend REST base URL |
| `GATEWAY_BACKEND_GRPC_ADDR` | `localhost:9090` | backend push gRPC address |
| `GATEWAY_BACKEND_TIMEOUT` | `5s` | per backend REST call |
| `GATEWAY_ADMIN_USER` / `GATEWAY_ADMIN_PASSWORD` | unset | enable + guard the admin console at `/_gm` |
| `GATEWAY_CONNECTOR_ADDR` | unset | Telegram connector gRPC address (enables initData validation + out-of-app push) |
| `GATEWAY_SESSION_TTL` | `10m` | cached session lifetime |
| `GATEWAY_SESSION_CACHE_MAX` | `50000` | cached session cap |
| `GATEWAY_PUSH_HEARTBEAT_INTERVAL` | `15s` | live-stream keep-alive |
| `GATEWAY_SERVICE_NAME` | `scrabble-gateway` | OpenTelemetry `service.name` |
| `GATEWAY_OTEL_TRACES_EXPORTER` | `none` | `none`, `stdout` or `otlp` (gRPC; endpoint from `OTEL_EXPORTER_OTLP_*`) |
| `GATEWAY_OTEL_METRICS_EXPORTER` | `none` | `none`, `stdout` or `otlp` |
Rate-limit defaults (built-in): public 30/min·IP (burst 10), authenticated
120/min·user (burst 40), admin 60/min·IP (burst 20), email-code 5/10 min·IP.
## Run
```sh
GATEWAY_BACKEND_HTTP_URL=http://localhost:8080 \
GATEWAY_BACKEND_GRPC_ADDR=localhost:9090 \
go run ./gateway/cmd/gateway # Connect edge on :8081
```
## Generated code
The Connect envelope Go is committed under `proto/edge/v1`. Regenerate after
editing the `.proto` (dev-time, like `backend/cmd/jetgen`):
```sh
make -C gateway tools # go install protoc-gen-go + protoc-gen-connect-go
make -C gateway gen # buf generate (local plugins)
```
The FlatBuffers payloads are generated in [`../pkg`](../pkg) (`make -C pkg fbs`).
## Tests
```sh
go test -count=1 ./gateway/...
```
All gateway tests are hermetic: no real network, a fake backend (`httptest`) and
credential fixtures. There is no integration (Docker) suite — the gateway holds
no database.