# Code Review — Client.Java

| Field | Value |
|---|---|
| Module | `clients/java` |
| Reviewer | Claude Code |
| Review date | 2026-05-18 |
| Commit reviewed | `3cc53a8` |
| Status | Reviewed |
| Open findings | 7 |

## Checklist coverage

| # | Category | Result |
|---|---|---|
| 1 | Correctness & logic bugs | Issues found: `register`/`addItem` silently fall back to `getReturnValue()` masking missing payloads (Client.Java-004); fragile `resolved()` mutation pattern (Client.Java-012). |
| 2 | mxaccessgw conventions | Largely adheres; the gateway protocol-version handshake is never verified despite the contract field existing (Client.Java-003). |
| 3 | Concurrency & thread safety | Issue found: `MxEventStream.next` is a plain field and terminal-state transitions race (Client.Java-002). |
| 4 | Error handling & resilience | Issues found: `close()` can mask the primary exception (Client.Java-005); async/sync error surfaces inconsistent (Client.Java-008). |
| 5 | Security | Issue found: API-key redaction leaks the trailing 4 secret characters (Client.Java-001). |
| 6 | Performance & resource management | Issues found: `close()` does not await termination (Client.Java-006); no stream flow control (Client.Java-011). |
| 7 | Design-document adherence | Matches `JavaClientDesign.md` closely; the protocol-version check is undocumented-missing (Client.Java-003). |
| 8 | Code organization & conventions | Issue found: ~80 duplicated lines across the two clients (Client.Java-009). |
| 9 | Testing coverage | Issue found: alarm RPCs, TLS setup, async streams, and queue overflow untested (Client.Java-007). |
| 10 | Documentation & comments | Issue found: README/Javadoc assert undocumented scope names (Client.Java-010). |

## Findings

### Client.Java-001

| Field | Value |
|---|---|
| Severity | Medium |
| Category | Security |
| Location | `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewaySecrets.java:30-32` |
| Status | Resolved |

**Description:** `redactApiKey` preserves the leading and trailing four characters of the key. A gateway API key has the form `mxgw_<key-id>_<secret>`; the last four characters belong to the secret portion, so the "redacted" form leaks 4 characters of the actual secret into logs, CLI JSON output (`CommonOptions.redactedJsonMap`), and `MxGatewayClientOptions.toString()`. CLAUDE.md states API keys must never reach logs.

**Recommendation:** Redact the secret entirely. Show only a stable non-secret prefix (e.g. the `mxgw_<key-id>_` portion) and mask everything after it, or emit a fixed `mxgw_***` form. Do not echo any trailing characters of the secret.

**Resolution:** (2026-05-18) Confirmed against source: the old `substring(0,4) + stars + substring(len-4)` echoed the last four secret characters. `redactApiKey` now masks the secret entirely: for gateway-shaped keys it returns the non-secret `mxgw_<key-id>_` prefix followed by `***` (locating the secret separator as the first `_` after `mxgw_`); any non-gateway-shaped token returns `<redacted>`. No leading/trailing secret characters are ever emitted. The pre-existing `MxGatewayCliTests.openSessionJsonRedactsApiKey` assertion that hardcoded the leaky `mxgw***********cret` form was corrected to assert the masked `mxgw_visible_***` form. Regression tests: `MxGatewayMediumFindingsTests.redactApiKeyDoesNotLeakAnyCharacterOfTheSecret`, `redactApiKeyForNonGatewayShapedKeyRevealsNothing`, `redactApiKeyStillHandlesNullAndShortInput`.

### Client.Java-002

| Field | Value |
|---|---|
| Severity | Medium |
| Category | Concurrency & thread safety |
| Location | `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxEventStream.java:31,66-92` |
| Status | Resolved |

**Description:** The `next` field is a plain (non-volatile) instance field, and `MxEventStream` exposes no thread-confinement guarantee. More concretely, a queue-overflow `offer()` and a `close()` `offer(END)` can interleave so the overflow exception is enqueued after `END` and never observed — the contract that "next() throws after overflow" is not guaranteed once `close()` has been called.

**Recommendation:** Document single-consumer-thread usage explicitly in the Javadoc, and serialise terminal state transitions (overflow vs END vs close) behind a single guarded flag so the first terminal condition wins deterministically.

**Resolution:** (2026-05-18) Confirmed against source: the old `offer()` END-branch did `queue.clear(); queue.offer(END)` when full, so a `close()` arriving after an overflow wiped the already-enqueued overflow exception, leaving the consumer with a clean end-of-stream and the overflow silently lost. Terminal transitions are now serialised through a single `terminate(MxGatewayException)` method guarded by a `terminated` flag and a `terminalLock`; the first terminal condition wins and a later `close()`/`END` cannot overwrite a published overflow fault. The Javadoc now explicitly documents that the iterator methods are single-consumer-only while `close()` is safe from any thread. Regression tests: `MxGatewayMediumFindingsTests.eventStreamOverflowExceptionSurvivesASubsequentClose` (deterministic) and `eventStreamConcurrentOverflowAndCloseAlwaysTerminate` (300-iteration race stress).

### Client.Java-003

| Field | Value |
|---|---|
| Severity | Medium |
| Category | mxaccessgw conventions |
| Location | `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayClient.java:119-140` |
| Status | Resolved |

**Description:** `OpenSessionReply` carries `gateway_protocol_version` (proto field 8), and `MxGatewayClientVersion.GATEWAY_PROTOCOL_VERSION` exists so the client can reject incompatible generated-code inputs. The client never reads `reply.getGatewayProtocolVersion()` nor compares it against the compiled-in version. A client built against an older/newer contract issues commands blindly and fails with confusing downstream errors instead of a clear version-mismatch failure.

**Recommendation:** In `openSession`/`openSessionRaw`, compare `reply.getGatewayProtocolVersion()` with `MxGatewayClientVersion.gatewayProtocolVersion()` and throw a typed `MxGatewayException` on mismatch.

**Resolution:** (2026-05-18) Confirmed against source: neither `openSessionRaw` nor `openSessionAsync` read `getGatewayProtocolVersion()`. Added a private `ensureGatewayProtocolCompatible` helper, called from both `openSessionRaw` and `openSessionAsync`, that throws `MxGatewayException` with a clear mismatch message when the gateway reports a non-zero version differing from `MxGatewayClientVersion.gatewayProtocolVersion()`. A gateway that leaves the field unset (value 0, e.g. an older gateway) is accepted unchanged for backward compatibility. `clients/java/README.md` documents the new fail-fast check. Regression tests: `MxGatewayMediumFindingsTests.openSessionRejectsIncompatibleGatewayProtocolVersion` and `openSessionAcceptsMatchingOrUnsetGatewayProtocolVersion`.

### Client.Java-004

| Field | Value |
|---|---|
| Severity | Medium |
| Category | Correctness & logic bugs |
| Location | `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewaySession.java:114-120,157-163,191-197` |
| Status | Resolved |

**Description:** `register`, `addItem`, and `addItem2` check `reply.hasRegister()`/`hasAddItem()` and otherwise fall back to `reply.getReturnValue().getInt32Value()`. If the gateway returns a reply with neither the typed payload nor a `return_value` set, the method silently returns `0` — indistinguishable from a legitimate handle of 0. This masks a contract violation rather than surfacing it.

**Recommendation:** If the expected typed payload is absent and no `return_value` is present, throw `MxGatewayException` (protocol violation) instead of returning `0`.

**Resolution:** (2026-05-18) Confirmed against source: all three methods returned `reply.getReturnValue().getInt32Value()` (which yields `0` for an unset message field) when the typed payload was absent. Each method now guards the fallback with `reply.hasReturnValue()` and throws `MxGatewayException` describing the protocol violation when neither the typed payload nor a `return_value` is present. The legitimate `return_value` fallback is preserved. Regression tests: `MxGatewayMediumFindingsTests.registerThrowsWhenReplyHasNeitherTypedPayloadNorReturnValue`, `addItemThrowsWhenReplyHasNeitherTypedPayloadNorReturnValue`, and `addItemStillHonoursReturnValueFallback`.

### Client.Java-005

| Field | Value |
|---|---|
| Severity | Medium |
| Category | Error handling & resilience |
| Location | `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewaySession.java:92-105` |
| Status | Resolved |

**Description:** `close()` delegates to `closeRaw()`, which performs a network RPC. When `MxGatewaySession` is used in try-with-resources and the body throws, a failure inside `closeSession` (e.g. `WORKER_UNAVAILABLE`) throws from `close()` and replaces the original exception as the propagated throwable (the body exception becomes a suppressed exception) — a known try-with-resources footgun for I/O-performing `close()`.

**Recommendation:** Either make `close()` swallow/log close-time failures (keeping `closeRaw()` for callers who want the result), or document clearly that `close()` performs a network call that can throw.

**Resolution:** (2026-05-18) Confirmed against source: `close()` called `closeRaw()` directly, so a `CloseSession` RPC failure propagated out of try-with-resources and replaced the body exception. `close()` now catches `MxGatewayException` from `closeRaw()` and logs it at WARNING via `System.Logger` instead of rethrowing, so a close-time failure never masks the body exception. `closeRaw()` is unchanged and still throws for callers who want to observe the close result. The behavior change and the recommendation to use `closeRaw()` for explicit close handling are documented in `clients/java/README.md` and the `close()` Javadoc. Regression tests: `MxGatewayMediumFindingsTests.closeSuppressesCloseTimeFailureInsteadOfMaskingBodyException` and `closeRawStillSurfacesCloseTimeFailureForCallersWhoWantIt`.

### Client.Java-006

| Field | Value |
|---|---|
| Severity | Low |
| Category | Performance & resource management |
| Location | `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayClient.java:323-328`, `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/GalaxyRepositoryClient.java:279-284` |
| Status | Open |

**Description:** `close()` (the `AutoCloseable` method invoked by try-with-resources) calls only `ownedChannel.shutdown()` and returns immediately without awaiting termination. In-flight calls and Netty event-loop threads may still be running when the caller assumes the resource is released. `closeAndAwaitTermination()` does it correctly but is not the method try-with-resources uses, and the README examples all rely on try-with-resources.

**Recommendation:** Have `close()` await termination for a bounded time and `shutdownNow()` on timeout (the logic already in `closeAndAwaitTermination()`), or document that try-with-resources callers should call `closeAndAwaitTermination()`.

**Resolution:** _(open)_

### Client.Java-007

| Field | Value |
|---|---|
| Severity | Low |
| Category | Testing coverage |
| Location | `clients/java/mxgateway-client/src/test/java/com/dohertylan/mxgateway/client/` |
| Status | Open |

**Description:** The alarm surface — `acknowledgeAlarm`/`acknowledgeAlarmAsync`/`queryActiveAlarms` and `MxGatewayActiveAlarmsSubscription` — has zero test coverage. TLS channel construction, the async `streamEventsAsync` path, `MxGatewayEventSubscription` pre-start cancellation, and `MxEventStream` queue overflow are likewise untested. `JavaClientDesign.md` explicitly lists async stream-observer cancellation and status/error mapping as required tests.

**Recommendation:** Add in-process gRPC tests for the alarm RPCs, the async streaming/subscription cancellation paths, and at least one TLS-config construction test.

**Resolution:** _(open)_

### Client.Java-008

| Field | Value |
|---|---|
| Severity | Low |
| Category | Error handling & resilience |
| Location | `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayClient.java:298-304` |
| Status | Open |

**Description:** `acknowledgeAlarmAsync` and `openSessionAsync` apply `ensureProtocolSuccess` inside `thenApply`. If that validator throws a non-`MxGatewayException` `RuntimeException` it is wrapped by `CompletionException` with no `fromGrpc` normalisation, unlike the synchronous paths which normalise via `try/catch`. The async and sync error surfaces are therefore inconsistent.

**Recommendation:** Wrap the `thenApply` body so any non-`MxGatewayException` is routed through `MxGatewayErrors.fromGrpc`, matching the synchronous methods.

**Resolution:** _(open)_

### Client.Java-009

| Field | Value |
|---|---|
| Severity | Low |
| Category | Code organization & conventions |
| Location | `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/GalaxyRepositoryClient.java:310-391`, `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayClient.java:346-413` |
| Status | Open |

**Description:** `createChannel`, `withDeadline`, `withStreamDeadline`, and `toCompletable` are duplicated nearly verbatim across `MxGatewayClient` and `GalaxyRepositoryClient` (~80 lines). A fix to one will not propagate to the other.

**Recommendation:** Extract the channel-builder and future-adaptor helpers into a shared package-private utility class.

**Resolution:** _(open)_

### Client.Java-010

| Field | Value |
|---|---|
| Severity | Low |
| Category | Documentation & comments |
| Location | `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayClient.java:269-272`, `clients/java/README.md:76` |
| Status | Open |

**Description:** The `acknowledgeAlarm` Javadoc states the gateway authenticates against an `invoke:alarm-ack` scope, and the README states the Galaxy Repository requires a `metadata:read` scope. CLAUDE.md's documented scope set names neither — the Javadoc/README assert a scope contract the project's own auth documentation does not corroborate.

**Recommendation:** Reconcile the scope names with `src/MxGateway.Server/Security/` and CLAUDE.md; correct the Javadoc/README to the actual scope strings, or fix CLAUDE.md if sub-scopes were genuinely added.

**Resolution:** _(open)_

### Client.Java-011

| Field | Value |
|---|---|
| Severity | Low |
| Category | Performance & resource management |
| Location | `clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxEventStream.java:37-63` |
| Status | Open |

**Description:** The event stream relies on default gRPC auto-inbound flow control: the async stub auto-requests messages, so the server can push faster than the 16-element bounded queue drains. A momentarily slow consumer triggers queue overflow and an immediate stream-fault cancel. This is consistent with the documented fail-fast event-backpressure design, but the client never applies real flow control, so even brief consumer stalls kill the subscription.

**Recommendation:** Confirm fail-fast is intended (it appears to be); if so, document it on `MxEventStream` so callers know a slow consumer terminates the stream. Optionally expose the queue capacity or opt-in flow control.

**Resolution:** _(open)_

### Client.Java-012

| Field | Value |
|---|---|
| Severity | Low |
| Category | Correctness & logic bugs |
| Location | `clients/java/mxgateway-cli/src/main/java/com/dohertylan/mxgateway/cli/MxGatewayCli.java:667-674` |
| Status | Open |

**Description:** `CommonOptions.resolved()` mutates `this` (`resolvedApiKey`, `resolvedTimeout`) and returns `this`, but `toClientOptions()` and `redactedJsonMap()` read those mutated fields. If `redactedJsonMap()` is ever called before `resolved()`, it silently emits empty-string defaults. The "return this after mutating" pattern is fragile and surprising.

**Recommendation:** Make `resolved()` return an immutable resolved value object, or compute `resolvedApiKey`/`resolvedTimeout` lazily in their getters so call ordering cannot produce stale output.

**Resolution:** _(open)_
