# NATS Strict Full Go Parity Design

**Date:** 2026-02-23  
**Status:** Approved  
**Scope:** Identify and close all remaining NATS functionality gaps between Go and .NET using behavior-level parity (not limited to existing parity-table status), with required unit/integration test coverage and parity-doc synchronization.

## 1. Architecture and Scope Boundary

### Closure model
Each parity capability closes only when all three are complete:

1. Behavior  
The .NET runtime behavior matches Go contract semantics at protocol and subsystem level.

2. Tests  
Positive and edge/failure tests exist and fail on regression.

3. Docs  
`differences.md` and parity artifacts reflect the validated behavior state.

### Scope interpretation
This cycle treats remaining parity as capability-level and code-backed, not as a direct read of current table status alone. Existing contradictions between prose claims and observable implementation are treated as parity debt and are in scope.

### Execution order
1. Inter-server fabric semantics (routes/gateway/leaf, account-scoped interest/delivery)  
2. Auth/account/config/monitor operational semantics  
3. JetStream runtime state machines  
4. JetStream storage durability + RAFT/cluster governance  
5. MQTT protocol/transport parity beyond current baseline  
6. Documentation and evidence synchronization

## 2. Component Plan

### A. Inter-server fabric parity
Primary files:
- `src/NATS.Server/NatsServer.cs`
- `src/NATS.Server/Routes/RouteConnection.cs`
- `src/NATS.Server/Routes/RouteManager.cs`
- `src/NATS.Server/Gateways/GatewayConnection.cs`
- `src/NATS.Server/Gateways/GatewayManager.cs`
- `src/NATS.Server/LeafNodes/LeafConnection.cs`
- `src/NATS.Server/LeafNodes/LeafNodeManager.cs`
- `src/NATS.Server/Subscriptions/SubList.cs`

Focus:
- account-correct remote delivery path (not global-only shortcuts)
- idempotent remote interest propagation under reconnect/duplicates
- durable reply-remap and loop-marker transparency rules

### B. MQTT protocol parity
Primary files:
- `src/NATS.Server/Mqtt/MqttProtocolParser.cs`
- `src/NATS.Server/Mqtt/MqttConnection.cs`
- `src/NATS.Server/Mqtt/MqttListener.cs`
- `src/NATS.Server/MqttOptions.cs`
- `src/NATS.Server/Configuration/ConfigProcessor.cs`

Focus:
- replace line-oriented pseudo protocol with byte-level MQTT packet parsing/writing
- implement connection/session/subscribe/publish acknowledgement contracts
- align MQTT auth/TLS/keepalive behavior with configured options

### C. JetStream runtime parity
Primary files:
- `src/NATS.Server/JetStream/JetStreamService.cs`
- `src/NATS.Server/JetStream/StreamManager.cs`
- `src/NATS.Server/JetStream/ConsumerManager.cs`
- `src/NATS.Server/JetStream/Consumers/AckProcessor.cs`
- `src/NATS.Server/JetStream/Consumers/PullConsumerEngine.cs`
- `src/NATS.Server/JetStream/Consumers/PushConsumerEngine.cs`
- `src/NATS.Server/JetStream/MirrorSource/*`

Focus:
- policy-divergent retention runtime behavior (`Limits/Interest/WorkQueue`)
- deterministic delivery/ack/backoff/replay/flow-control state-machine transitions
- mirror/source behavior under filters, transform, and cross-account paths

### D. Storage + RAFT + governance parity
Primary files:
- `src/NATS.Server/JetStream/Storage/FileStore.cs`
- `src/NATS.Server/JetStream/Storage/MemStore.cs`
- `src/NATS.Server/Raft/RaftNode.cs`
- `src/NATS.Server/Raft/RaftReplicator.cs`
- `src/NATS.Server/Raft/RaftTransport.cs`
- `src/NATS.Server/Raft/RaftSnapshotStore.cs`
- `src/NATS.Server/JetStream/Cluster/JetStreamMetaGroup.cs`
- `src/NATS.Server/JetStream/Cluster/StreamReplicaGroup.cs`

Focus:
- durability invariants across restart/prune/recovery cycles
- term/quorum/next-index/snapshot/membership semantics with convergence behavior
- meta/replica governance actions reflected in committed state and routing outcomes

### E. Operational parity surfaces
Primary files:
- `src/NATS.Server/Monitoring/MonitorServer.cs`
- `src/NATS.Server/Monitoring/PprofHandler.cs`
- `src/NATS.Server/Configuration/ConfigReloader.cs`
- `src/NATS.Server/NatsOptions.cs`
- `src/NATS.Server/Events/InternalEventSystem.cs`

Focus:
- replace synthetic profiling behavior with parity-meaningful runtime profiling outputs
- close option-surface vs runtime-semantics drift for key advanced options
- align event/monitor behavior with capability claims

### F. Documentation and evidence
Primary files:
- `differences.md`
- `docs/plans/2026-02-23-jetstream-remaining-parity-map.md`
- `docs/plans/2026-02-23-jetstream-remaining-parity-verification.md`

Focus:
- remove contradictory parity claims
- ensure every claimed closure maps to concrete behavior and test evidence

## 3. Data Flow and Behavioral Contracts

1. Inter-server delivery contract  
- route/gateway/leaf inbound delivery resolves with correct account scope and permissions  
- reply-remap and leaf-loop markers remain transport-internal and reversible  
- remote interest convergence stays idempotent across reconnect churn

2. MQTT protocol contract  
- fixed-header/remaining-length packet framing must be valid on read/write paths  
- QoS/session/ack transitions must be deterministic and stateful  
- auth and account association must fail closed on invalid credentials or malformed packets

3. JetStream stream contract  
- retention modes diverge by runtime behavior, not only config parsing  
- preconditions and policy guards execute before irreversible storage changes  
- max-age/per-subject/dedupe behavior remains consistent under load and restart

4. JetStream consumer contract  
- deliver policy cursor initialization and progression are deterministic  
- ack/redelivery/backoff/max-deliver transitions preserve monotonic pending/floor invariants  
- push/pull flows maintain consistent flow-control and replay timing contracts

5. Storage/RAFT/governance contract  
- stream/store state invariants remain stable after prune/recovery/snapshot cycles  
- commit visibility is quorum-gated with stale-term and mismatch handling  
- governance actions (stepdown/placement/cluster forwarding) reflect committed consensus state

## 4. Error Handling, Testing Strategy, and Completion Gates

### Error handling
1. Preserve protocol-specific error surfaces across NATS, JetStream, and MQTT.  
2. Fail closed on account-scoping, authorization, and consensus-precondition violations.  
3. Prevent partial mutation on multi-step operations (publish+replicate, control+governance).

### Testing strategy
1. Test-first per capability batch (failing test first, then minimal implementation).  
2. Each capability requires positive + edge/failure coverage.  
3. Multi-node, transport, RAFT, and MQTT protocol semantics use integration tests; low-level state transitions use focused unit tests.  
4. No parity claim is accepted from docs-only or hook-only evidence.

### Completion gates
1. Capability closes only with Behavior + Tests + Docs complete.  
2. Full verification gate must pass:
- focused suites for each completed batch
- `dotnet test -v minimal`
3. `differences.md` may only claim closure where behavior is demonstrably ported.  
4. Deferred parity items are allowed only with explicit blocker rationale and observable evidence.
