# Implementation Gaps: Go NATS Server vs .NET Port

**Last updated:** 2026-02-25

## Overview

| Metric | Go Server | .NET Port | Ratio |
|--------|-----------|-----------|-------|
| Source lines | ~130K (109 files) | ~39.1K (215 files) | 3.3x |
| Test methods | 2,937 `func Test*` | 5,808 `[Fact]`/`[Theory]` (~6,409 with parameterized) | 2.0x |
| Go tests mapped | 2,646 / 2,937 (90.1%) | — | — |
| .NET tests linked to Go | — | 2,485 / 5,808 (42.8%) | — |
| Largest source file | filestore.go (12,593 lines) | NatsServer.cs (1,883 lines) | 6.7x |

The .NET port has grown significantly from the prior baseline (~27K→~39.1K lines). All 15 original gaps have seen substantial growth. However, many specific features within each subsystem remain unimplemented. This document catalogs the remaining gaps based on a function-by-function comparison.

## Gap Severity Legend

- **CRITICAL**: Core functionality missing, blocks production use
- **HIGH**: Important feature incomplete, limits capabilities significantly
- **MEDIUM**: Feature gap exists but workarounds are possible or feature is less commonly used
- **LOW**: Nice-to-have, minor optimization or edge-case handling

---

## Gap 1: FileStore Block Management (CRITICAL)

**Go reference**: `filestore.go` — 12,593 lines
**NET implementation**: `FileStore.cs` (1,633) + `MsgBlock.cs` (630) + supporting files
**Current .NET total**: ~5,196 lines in Storage/
**Gap factor**: 2.4x (down from 20.8x)

The .NET FileStore has grown substantially with block-based storage, but the block lifecycle, encryption/compression integration, crash recovery, and integrity checking remain incomplete.

### 1.1 Block Rotation & Lifecycle (CRITICAL)

**Missing Go functions:**
- `initMsgBlock()` (line 1046) — initializes new block with metadata
- `recoverMsgBlock()` (line 1148) — recovers block from disk with integrity checks
- `newMsgBlockForWrite()` (line 4485) — creates writable block with locking
- `spinUpFlushLoop()` + `flushLoop()` (lines 5783–5842) — background flusher goroutine
- `enableForWriting()` (line 6622) — opens FD for active block with gating semaphore (`dios`)
- `closeFDs()` / `closeFDsLocked()` (lines 6843–6849) — explicit FD management
- `shouldCompactInline()` (line 5553) — inline compaction heuristics
- `shouldCompactSync()` (line 5561) — sync-time compaction heuristics

**.NET status**: Basic block creation/recovery exists but no automatic rotation on size thresholds, no block sealing, no per-block metadata files, no background flusher.

### 1.2 Encryption Integration into Block I/O (CRITICAL)

Go encrypts block files on disk using per-block AEAD keys. The .NET `AeadEncryptor` exists as a standalone utility but is NOT wired into the block write/read path.

**Missing Go functions:**
- `genEncryptionKeys()` (line 816) — generates AEAD + stream cipher per block
- `recoverAEK()` (line 878) — recovers encryption key from metadata
- `setupAEK()` (line 907) — sets up encryption for the stream
- `loadEncryptionForMsgBlock()` (line 1078) — loads per-block encryption state
- `checkAndLoadEncryption()` (line 1068) — verifies encrypted block integrity
- `ensureLastChecksumLoaded()` (line 1139) — validates block checksum
- `convertCipher()` (line 1318) — re-encrypts block with new cipher
- `convertToEncrypted()` (line 1407) — converts plaintext block to encrypted

**Impact**: Go provides end-to-end encryption of block files on disk. .NET stores block files in plaintext.

### 1.3 S2 Compression in Block Path (CRITICAL)

Go compresses payloads at the message level during block write and decompresses on read. .NET's `S2Codec` is standalone only.

**Missing Go functions:**
- `setupWriteCache()` (line 4443) — initializes compression-aware write cache
- Block-level compression/decompression during loadMsgs/flushPendingMsgs

**Impact**: Go block files are compressed (smaller disk footprint). .NET block files are uncompressed.

### 1.4 Crash Recovery & Index Rebuilding (CRITICAL)

**Missing Go functions:**
- `recoverFullState()` (line 1754) — full recovery from blocks with lost-data tracking
- `recoverTTLState()` (line 2042) — recovers TTL wheel state post-crash
- `recoverMsgSchedulingState()` (line 2123) — recovers scheduled message delivery post-crash
- `recoverMsgs()` (line 2263) — scans all blocks and rebuilds message index
- `rebuildState()` (line 1446) — per-block state reconstruction
- `rebuildStateFromBufLocked()` (line 1493) — parses raw block buffer to rebuild state
- `expireMsgsOnRecover()` (line 2401) — enforces MaxAge on recovery
- `writeTTLState()` (line 10833) — persists TTL state to disk

**.NET status**: `FileStore.RecoverBlocks()` exists but is minimal — no TTL wheel recovery, no scheduling recovery, no lost-data tracking, no tombstone cleanup.

### 1.5 Checksum Validation (HIGH)

Go uses highway hash for per-message checksums and validates integrity on read.

**Missing:**
- `msgBlock.lchk[8]byte` — last checksum buffer
- `msgBlock.hh *highwayhash.Digest64` — highway hasher
- `msgBlock.lastChecksum()` (line 2204) — returns last computed checksum
- Message checksum validation during `msgFromBufEx()` (line ~8180)

**.NET status**: `MessageRecord` has no checksum field. No integrity checks on read.

### 1.6 Atomic File Overwrites (HIGH)

Go uses temp file + rename for crash-safe state updates.

**Missing:**
- `_writeFullState()` (line 10599) — atomic state serialization with temp file + rename
- State file write protection with mutual exclusion (`wfsmu`/`wfsrun`)

**.NET status**: Writes directly without atomic guarantees.

### 1.7 Tombstone & Deletion Tracking (HIGH)

**Missing:**
- `removeMsg()` (line 5267) — removes message with optional secure erase
- `removeMsgFromBlock()` (line 5307) — removes from specific block
- `eraseMsg()` (line 5890) — overwrites deleted message with random data (secure erase)
- Sparse `avl.SequenceSet` for deletion tracking (Go uses AVL; .NET uses `HashSet<ulong>`)
- Tombstone record persistence (deleted messages lost on crash in .NET)

### 1.8 Multi-Block Write Cache (MEDIUM)

**Missing Go functions:**
- `setupWriteCache()` (line 4443) — sets up write cache
- `finishedWithCache()` (line 4477) — marks cache complete
- `expireCache()` / `expireCacheLocked()` (line 6148+) — expires idle cache
- `resetCacheExpireTimer()` / `startCacheExpireTimer()` — manages cache timeout
- Elastic reference machinery (line 6704, `ecache.Strengthen()` / `WeakenAfter()`)
- `flushPendingMsgs()` / `flushPendingMsgsLocked()` (line 7560+) — background flush

**.NET status**: Synchronous flush on rotation; no background flusher, no cache expiration.

### 1.9 Missing IStreamStore Interface Methods (CRITICAL)

| Method | Go Equivalent | .NET Status |
|--------|---------------|-------------|
| `StoreRawMsg` | filestore.go:4759 | Missing |
| `LoadNextMsgMulti` | filestore.go:8426 | Missing |
| `LoadPrevMsg` | filestore.go:8580 | Missing |
| `LoadPrevMsgMulti` | filestore.go:8634 | Missing |
| `NumPendingMulti` | filestore.go:4051 | Missing |
| `SyncDeleted` | — | Missing |
| `EncodedStreamState` | filestore.go:10599 | Missing |
| `Utilization` | filestore.go:8758 | Missing |
| `FlushAllPending` | — | Missing |
| `RegisterStorageUpdates` | filestore.go:4412 | Missing |
| `RegisterStorageRemoveMsg` | filestore.go:4424 | Missing |
| `RegisterProcessJetStreamMsg` | filestore.go:4431 | Missing |
| `ResetState` | filestore.go:8788 | Missing |
| `UpdateConfig` | filestore.go:655 | Stubbed |
| `Delete(bool)` | — | Incomplete |
| `Stop()` | — | Incomplete |

### 1.10 Query/Filter Operations (MEDIUM)

Go uses trie-based subject indexing (`SubjectTree[T]`) for O(log n) lookups. .NET uses linear LINQ scans.

**Missing:**
- `FilteredState()` (line 3191) — optimized filtered state with caching
- `checkSkipFirstBlock()` family (lines 3241–3287)
- `numFiltered*()` family (lines 3308–3413)
- `LoadMsg()` (line 8308) — block-aware message loading

---

## Gap 2: JetStream Cluster Coordination (CRITICAL)

**Go reference**: `jetstream_cluster.go` — 10,887 lines
**NET implementation**: `JetStreamMetaGroup.cs` (454) + `StreamReplicaGroup.cs` (300) + supporting files
**Current .NET total**: ~2,787 lines in Cluster/ + Raft/
**Gap factor**: ~3.9x
**Missing functions**: ~84

The .NET implementation provides a skeleton suitable for unit testing but lacks the real cluster coordination machinery. The Go implementation is deeply integrated with RAFT, NATS subscriptions for inter-node communication, and background monitoring goroutines.

### 2.1 Cluster Monitoring Loop (CRITICAL)

The main orchestration loop that drives cluster state transitions.

**Missing Go functions:**
- `monitorCluster()` (lines 1455–1825, 370 lines) — processes metadata changes from RAFT ApplyQ
- `checkForOrphans()` (lines 1378–1432) — identifies unmatched streams/consumers after recovery
- `getOrphans()` (lines 1433–1454) — scans all accounts for orphaned assets
- `checkClusterSize()` (lines 1828–1869) — detects mixed-mode clusters, adjusts bootstrap size
- `isStreamCurrent()`, `isStreamHealthy()`, `isConsumerHealthy()` (lines 582–679)
- `subjectsOverlap()` (lines 751–767) — prevents subject collisions
- Recovery state machine (`recoveryUpdates` struct, lines 1332–1366)

### 2.2 Stream & Consumer Assignment Processing (CRITICAL)

**Missing Go functions:**
- `processStreamAssignment()` (lines 4541–4647, 107 lines)
- `processUpdateStreamAssignment()` (lines 4650–4768)
- `processStreamRemoval()` (lines 5216–5265)
- `processConsumerAssignment()` (lines 5363–5542, 180 lines)
- `processConsumerRemoval()` (lines 5543–5599)
- `processClusterCreateStream()` (lines 4944–5215, 272 lines)
- `processClusterDeleteStream()` (lines 5266–5362, 97 lines)
- `processClusterCreateConsumer()` (lines 5600–5855, 256 lines)
- `processClusterDeleteConsumer()` (lines 5856–5925)
- `processClusterUpdateStream()` (lines 4798–4943, 146 lines)

### 2.3 Inflight Request Deduplication (HIGH)

**Missing:**
- `trackInflightStreamProposal()` (lines 1193–1210)
- `removeInflightStreamProposal()` (lines 1214–1230)
- `trackInflightConsumerProposal()` (lines 1234–1257)
- `removeInflightConsumerProposal()` (lines 1260–1278)
- Full inflight tracking with ops count, deleted flag, and assignment capture

### 2.4 Peer Management & Stream Moves (HIGH)

**Missing:**
- `processAddPeer()` (lines 2290–2340)
- `processRemovePeer()` (lines 2342–2393)
- `removePeerFromStream()` / `removePeerFromStreamLocked()` (lines 2396–2439)
- `remapStreamAssignment()` (lines 7077–7111)
- Stream move operations in `jsClusteredStreamUpdateRequest()` (lines 7757+)

### 2.5 Leadership Transition (HIGH)

**Missing:**
- `processLeaderChange()` (lines 7001–7074) — meta-level leader change
- `processStreamLeaderChange()` (lines 4262–4458, 197 lines) — stream-level
- `processConsumerLeaderChange()` (lines 6622–6793, 172 lines) — consumer-level
- Step-down mechanisms: `JetStreamStepdownStream()`, `JetStreamStepdownConsumer()`

### 2.6 Snapshot & State Recovery (HIGH)

**Missing:**
- `metaSnapshot()` (line 1890) — triggers meta snapshot
- `encodeMetaSnapshot()` (lines 2075–2145) — binary+S2 compression
- `decodeMetaSnapshot()` (lines 2031–2074) — reverse of encode
- `applyMetaSnapshot()` (lines 1897–2030, 134 lines) — computes deltas and applies
- `collectStreamAndConsumerChanges()` (lines 2146–2240)
- Per-stream `monitorStream()` (lines 2895–3700, 800+ lines)
- Per-consumer `monitorConsumer()` (lines 6081–6350, 270+ lines)

### 2.7 Entry Application Pipeline (HIGH)

**Missing:**
- `applyMetaEntries()` (lines 2474–2609, 136 lines) — handles all entry types
- `applyStreamEntries()` (lines 3645–4067, 423 lines) — per-stream entries
- `applyStreamMsgOp()` (lines 4068–4261, 194 lines) — per-message ops
- `applyConsumerEntries()` (lines 6351–6621, 271 lines) — per-consumer entries

### 2.8 Topology-Aware Placement (MEDIUM)

**Missing from PlacementEngine (currently 80 lines vs Go's 312 lines for `selectPeerGroup()`):**
- Unique tag enforcement (`JetStreamUniqueTag`)
- HA asset limits per peer
- Dynamic available storage calculation
- Tag inclusion/exclusion with prefix handling
- Weighted node selection based on availability
- Mixed-mode detection
- `tieredStreamAndReservationCount()` (lines 7524–7546)
- `createGroupForConsumer()` (lines 8783–8923, 141 lines)
- `jsClusteredStreamLimitsCheck()` (lines 7599–7618)

### 2.9 RAFT Group Creation & Lifecycle (MEDIUM)

**Missing:**
- `createRaftGroup()` (lines 2659–2789, 131 lines)
- `raftGroup.isMember()` (lines 2611–2621)
- `raftGroup.setPreferred()` (lines 2623–2656)

### 2.10 Assignment Encoding/Decoding (MEDIUM)

**Missing (no serialization for RAFT persistence):**
- `encodeAddStreamAssignment()`, `encodeUpdateStreamAssignment()`, `encodeDeleteStreamAssignment()`
- `decodeStreamAssignment()`, `decodeStreamAssignmentConfig()`
- `encodeAddConsumerAssignment()`, `encodeDeleteConsumerAssignment()`
- `encodeAddConsumerAssignmentCompressed()`, `decodeConsumerAssignment()`
- `decodeConsumerAssignmentCompressed()`, `decodeConsumerAssignmentConfig()`

### 2.11 Unsupported Asset Handling (LOW)

**Missing:**
- `unsupportedStreamAssignment` type (lines 186–247) — graceful handling of version-incompatible streams
- `unsupportedConsumerAssignment` type (lines 268–330)

### 2.12 Clustered API Handlers (MEDIUM)

**Missing:**
- `jsClusteredStreamRequest()` (lines 7620–7701, 82 lines)
- `jsClusteredStreamUpdateRequest()` (lines 7757–8265, 509 lines)
- System-level subscriptions for result processing, peer removal, leadership step-down

---

## Gap 3: Consumer Delivery Engines (HIGH)

**Go reference**: `consumer.go` — 6,715 lines, 209 functions
**NET implementation**: `PushConsumerEngine.cs` (264) + `PullConsumerEngine.cs` (411) + `AckProcessor.cs` (225) + `PriorityGroupManager.cs` (102) + `RedeliveryTracker.cs` (92) + `ConsumerManager.cs` (198)
**Current .NET total**: ~1,292 lines
**Gap factor**: 5.2x

### 3.1 Core Message Delivery Loop (CRITICAL)

**Missing**: `loopAndGatherMsgs()` (Go lines ~1400–1700) — the main consumer dispatch loop that:
- Polls stream store for new messages matching filter
- Applies redelivery logic
- Handles num_pending calculations
- Manages delivery interest tracking
- Responds to stream updates

### 3.2 Pull Request Pipeline (CRITICAL)

**Missing**: `processNextMsgRequest()` (Go lines ~4276–4450) — full pull request handler with:
- Waiting request queue management (`waiting` list with priority)
- Max bytes accumulation and flow control
- Request expiry handling
- Batch size enforcement
- Pin ID assignment from priority groups

### 3.3 Inbound Ack/NAK Processing Loop (HIGH)

**Missing**: `processInboundAcks()` (Go line ~4854) — background goroutine that:
- Reads from ack subject subscription
- Parses `+ACK`, `-NAK`, `+TERM`, `+WPI` frames
- Dispatches to appropriate handlers
- Manages ack deadlines and redelivery scheduling

### 3.4 Redelivery Scheduler (HIGH)

**Missing**: Redelivery queue (`rdq`) as a min-heap/priority queue. `RedeliveryTracker` only tracks deadlines, doesn't:
- Order redeliveries by deadline
- Batch redelivery dispatches efficiently
- Support per-sequence redelivery state
- Handle redelivery rate limiting

### 3.5 Idle Heartbeat & Flow Control (HIGH)

**Missing**:
- `sendIdleHeartbeat()` (Go line ~5222) — heartbeat with pending counts and stall headers
- `sendFlowControl()` (Go line ~5495) — dedicated flow control handler
- Flow control reply generation with pending counts

### 3.6 Priority Group Pinning (HIGH)

`PriorityGroupManager` exists (102 lines) but missing:
- Pin ID (NUID) generation and assignment (`setPinnedTimer`, `assignNewPinId`, `unassignPinId`)
- Pin timeout timers (`pinnedTtl`)
- `Nats-Pin-Id` header response
- Advisory messages on pin/unpin events
- Priority group state persistence

### 3.7 Pause/Resume State Management (HIGH)

**Missing**:
- `PauseUntil` deadline tracking
- Pause expiry timer
- Pause advisory generation (`$JS.EVENT.ADVISORY.CONSUMER.PAUSED`)
- Resume/unpause event generation
- Pause state in consumer info response

### 3.8 Delivery Interest Tracking (HIGH)

**Missing**: Dynamic delivery interest monitoring:
- Subject interest change tracking
- Gateway interest checks
- Subscribe/unsubscribe tracking for delivery subject
- Interest-driven consumer cleanup (`deleteNotActive`)

### 3.9 Max Deliveries Enforcement (MEDIUM)

`AckProcessor` checks basic threshold but missing:
- Advisory event generation on exceeding max delivers
- Per-delivery-count policy selection
- `NotifyDeliveryExceeded` advisory

### 3.10 Filter Subject Skip Tracking (MEDIUM)

**Missing**: Efficient filter matching with compiled regex, skip list tracking, `UpdateSkipped` state updates.

### 3.11 Sample/Observe Mode (MEDIUM)

**Missing**: Sample frequency parsing (`"1%"`), stochastic sampling, latency measurement, latency advisory generation.

### 3.12 Reset to Sequence (MEDIUM)

**Missing**: `processResetReq()` (Go line ~4241) — consumer state reset to specific sequence.

### 3.13 Rate Limiting (MEDIUM)

`PushConsumerEngine` has basic rate limiting but missing accurate token bucket, dynamic updates, per-message delay calculation.

### 3.14 Cluster-Aware Pending Requests (LOW)

**Missing**: Pull request proposals to RAFT, cluster-wide pending request tracking.

---

## Gap 4: Stream Mirrors, Sources & Lifecycle (HIGH)

**Go reference**: `stream.go` — 8,072 lines, 193 functions
**NET implementation**: `StreamManager.cs` (644) + `MirrorCoordinator.cs` (364) + `SourceCoordinator.cs` (470)
**Current .NET total**: ~1,478 lines
**Gap factor**: 5.5x

### 4.1 Mirror Consumer Setup & Retry (HIGH)

`MirrorCoordinator` (364 lines) exists but missing:
- Complete mirror consumer API request generation
- Consumer configuration with proper defaults
- Subject transforms for mirror
- Filter subject application
- OptStartSeq/OptStartTime handling
- Mirror error state tracking (`setMirrorErr`)
- Scheduled retry with exponential backoff
- Mirror health checking

### 4.2 Mirror Message Processing (HIGH)

**Missing from MirrorCoordinator:**
- Gap detection in mirror stream (deleted/expired messages)
- Sequence alignment (`sseq`/`dseq` tracking)
- Mirror-specific handling for out-of-order arrival
- Mirror error advisory generation

### 4.3 Source Consumer Setup (HIGH)

`SourceCoordinator` (470 lines) exists but missing:
- Complete source consumer API request generation
- Subject filter configuration
- Subject transform setup
- Account isolation verification
- Flow control configuration
- Starting sequence selection logic

### 4.4 Deduplication Window Management (HIGH)

`SourceCoordinator` has `_dedupWindow` but missing:
- Time-based window pruning
- Memory-efficient cleanup
- Statistics reporting (`DeduplicatedCount`)
- `Nats-Msg-Id` header extraction integration

### 4.5 Purge with Subject Filtering (HIGH)

**Missing**:
- Subject-specific purge (`preq.Subject`)
- Sequence range purge (`preq.Sequence`)
- Keep-N functionality (`preq.Keep`)
- Consumer purge cascading based on filter overlap

### 4.6 Interest Retention Enforcement (HIGH)

**Missing**:
- Interest-based message cleanup (`checkInterestState`/`noInterest`)
- Per-consumer interest tracking
- `noInterestWithSubject` for filtered consumers
- Orphan message cleanup

### 4.7 Stream Snapshot & Restore (MEDIUM)

`StreamSnapshotService` is a 10-line stub. Missing:
- Snapshot deadline enforcement
- Consumer inclusion/exclusion
- TAR + S2 compression/decompression
- Snapshot validation
- Partial restore recovery

### 4.8 Stream Config Update Validation (MEDIUM)

**Missing**:
- Subjects overlap checking
- Mirror/source config validation
- Subjects modification handling
- Template update propagation
- Discard policy enforcement

### 4.9 Source Retry & Health (MEDIUM)

**Missing**:
- `retrySourceConsumerAtSeq()` — retry with exponential backoff
- `cancelSourceConsumer()` — source consumer cleanup
- `retryDisconnectedSyncConsumers()` — periodic health check
- `setupSourceConsumers()` — bulk initialization
- `stopSourceConsumers()` — coordinated shutdown

### 4.10 Source/Mirror Info Reporting (LOW)

**Missing**: Source/mirror lag, error state, consumer info for monitoring responses.

---

## Gap 5: Client Protocol Handling (HIGH)

**Go reference**: `client.go` — 6,716 lines, 162+ functions
**NET implementation**: `NatsClient.cs` (924 lines)
**Gap factor**: 7.3x

### 5.1 Flush Coalescing (HIGH)

**Missing**: Flush signal pending counter (`fsp`), `maxFlushPending=10`, `pcd` map of pending clients for broadcast-style flush signaling. Go allows multiple producers to queue data, then ONE flush signals the writeLoop. .NET uses independent channels per client.

### 5.2 Stall Gate Backpressure (HIGH)

**Missing**: `c.out.stc` channel that blocks producers when client is 75% full. No producer rate limiting in .NET.

### 5.3 Write Timeout with Partial Flush Recovery (HIGH)

**Missing**:
- Partial flush recovery logic (`written > 0` → retry vs close)
- `WriteTimeoutPolicy` enum (`Close`, `TcpFlush`)
- Different handling per client kind (routes can recover, clients cannot)
- .NET immediately closes on timeout; Go allows ROUTER/GATEWAY/LEAF to continue

### 5.4 Per-Account Subscription Result Cache (HIGH)

**Missing**: `readCache` struct with per-account results cache, route targets, statistical counters. Go caches Sublist match results per account on route/gateway inbound path (maxPerAccountCacheSize=8192).

### 5.5 Slow Consumer Stall Gate (MEDIUM)

**Missing**: Full stall gate mechanics — Go creates a channel blocking producers at 75% threshold, per-kind slow consumer statistics (route, gateway, leaf), account-level slow consumer tracking.

### 5.6 Dynamic Write Buffer Pooling (MEDIUM)

`OutboundBufferPool` exists but missing flush coalescing integration, `pcd` broadcast optimization.

### 5.7 Per-Client Trace Level (MEDIUM)

`SetTraceMode()` exists but missing message delivery tracing (`traceMsgDelivery`) for routed messages, per-client echo support.

### 5.8 Subscribe Permission Caching (MEDIUM)

`PermissionLruCache` caches PUB permissions but NOT SUB. Go caches per-account results with genid-based invalidation.

### 5.9 Internal Client Kinds (LOW)

`ClientKind` enum supports CLIENT, ROUTER, GATEWAY, LEAF but missing SYSTEM, JETSTREAM, ACCOUNT kinds and `isInternalClient()` predicate.

### 5.10 Adaptive Read Buffer Short-Read Counter (LOW)

`AdaptiveReadBuffer` implements 2x grow/shrink but missing Go's `srs` (short reads) counter for more precise shrink decisions.

---

## Gap 6: MQTT Protocol (HIGH)

**Go reference**: `mqtt.go` — 5,882 lines
**NET implementation**: `Mqtt/` — 1,238 lines (8 files)
**Gap factor**: 4.7x

### 6.1 JetStream-Backed Session Persistence (CRITICAL)

**Missing**: Go creates dedicated JetStream streams for:
- `$MQTT_msgs` — message persistence
- `$MQTT_rmsgs` — retained messages
- `$MQTT_sess` — session state
- `$MQTT_qos2in` — QoS 2 incoming tracking
- `$MQTT_out` — QoS 1/2 outgoing

.NET MQTT is entirely in-memory. Sessions are lost on restart.

### 6.2 Will Message Delivery (HIGH)

`MqttSessionStore` stores will metadata (`WillTopic`, `WillPayload`, `WillQoS`, `WillRetain`) but does NOT publish the will message on abnormal client disconnection.

### 6.3 QoS 1/2 Tracking (HIGH)

`MqttQoS2StateMachine` exists for QoS 2 state transitions but missing:
- JetStream-backed QoS 1 acknowledgment tracking
- Durable redelivery of unacked QoS 1/2 messages
- PUBREL delivery stream for QoS 2 phase 2

### 6.4 MaxAckPending Enforcement (HIGH)

**Missing**: No backpressure mechanism for QoS 1 accumulation, no per-subscription limits, no config reload hook.

### 6.5 Retained Message Delivery on Subscribe (MEDIUM)

`MqttRetainedStore` exists but not JetStream-backed and not integrated with subscription handling — retained messages aren't delivered on SUBSCRIBE.

### 6.6 Session Flapper Detection (LOW)

Partially implemented in `MqttSessionStore` (basic structure present) but integration unclear.

---

## Gap 7: JetStream API Layer (MEDIUM)

**Go reference**: `jetstream_api.go` (5,165) + `jetstream.go` (2,866) = 8,031 lines
**NET implementation**: ~1,374 lines across 11 handler files
**Gap factor**: 5.8x

### 7.1 Leader Forwarding (HIGH)

API requests arriving at non-leader nodes must be forwarded to the current leader. Not implemented.

### 7.2 Clustered API Handlers (HIGH)

**Missing**:
- `jsClusteredStreamRequest()` — stream create in clustered mode
- `jsClusteredStreamUpdateRequest()` — update/delete/move/scale (509 lines in Go)
- Cluster-aware consumer create/delete handlers

### 7.3 API Rate Limiting & Deduplication (MEDIUM)

No request deduplication or rate limiting.

### 7.4 Snapshot & Restore API (MEDIUM)

No snapshot/restore API endpoints.

### 7.5 Consumer Pause/Resume API (MEDIUM)

No consumer pause/resume API endpoint.

### 7.6 Advisory Event Publication (LOW)

No advisory events for API operations.

---

## Gap 8: RAFT Consensus (CRITICAL for clustering)

**Go reference**: `raft.go` — 5,037 lines
**NET implementation**: `Raft/` — 1,838 lines (17 files)
**Gap factor**: 2.7x

### 8.1 Persistent Log Storage (CRITICAL)

.NET RAFT uses in-memory log only. RAFT state is not persisted across restarts.

### 8.2 Joint Consensus for Membership Changes (CRITICAL)

Current single-membership-change approach is unsafe for multi-node clusters. Go implements safe addition/removal per Section 4 of the RAFT paper.

### 8.3 InstallSnapshot Streaming (HIGH)

`RaftSnapshot` is fully loaded into memory. Go streams snapshots in chunks with progress tracking.

### 8.4 Leadership Transfer (MEDIUM)

No graceful leader step-down mechanism for maintenance operations.

### 8.5 Log Compaction (MEDIUM)

Basic compaction exists but no configurable retention policies.

### 8.6 Quorum Check Before Proposing (MEDIUM)

May propose entries when quorum is unreachable.

### 8.7 Read-Only Query Optimization (LOW)

All queries append log entries; no ReadIndex optimization for read-only commands.

### 8.8 Election Timeout Jitter (LOW)

May not have sufficient randomized jitter to prevent split votes.

---

## Gap 9: Account Management & Multi-Tenancy (MEDIUM)

**Go reference**: `accounts.go` — 4,774 lines, 172+ functions
**NET implementation**: `Account.cs` (280) + auth files
**Current .NET total**: ~1,266 lines
**Gap factor**: 3.8x

### 9.1 Service Export Latency Tracking (MEDIUM)

**Missing**: `TrackServiceExport()`, `UnTrackServiceExport()`, latency sampling, p50/p90/p99 tracking, `sendLatencyResult()`, `sendBadRequestTrackingLatency()`, `sendReplyInterestLostTrackLatency()`.

### 9.2 Service Export Response Threshold (MEDIUM)

**Missing**: `ServiceExportResponseThreshold()`, `SetServiceExportResponseThreshold()` for SLA limits.

### 9.3 Stream Import Cycle Detection (MEDIUM)

Only service import cycles detected. **Missing**: `streamImportFormsCycle()`, `checkStreamImportsForCycles()`.

### 9.4 Wildcard Service Exports (MEDIUM)

**Missing**: `getWildcardServiceExport()` — cannot define wildcard exports like `svc.*`.

### 9.5 Account Expiration & TTL (MEDIUM)

**Missing**: `IsExpired()`, `expiredTimeout()`, `setExpirationTimer()` — expired accounts won't auto-cleanup.

### 9.6 Account Claim Hot-Reload (MEDIUM)

**Missing**: `UpdateAccountClaims()`, `updateAccountClaimsWithRefresh()` — account changes may require restart.

### 9.7 Service/Stream Activation Expiration (LOW)

**Missing**: JWT activation claim expiry enforcement.

### 9.8 User NKey Revocation (LOW)

**Missing**: `checkUserRevoked()` — cannot revoke individual users without re-deploying.

### 9.9 Response Service Import (LOW)

**Missing**: Reverse response mapping for cross-account request-reply (`addReverseRespMapEntry`, `checkForReverseEntries`).

### 9.10 Service Import Shadowing Detection (LOW)

**Missing**: `serviceImportShadowed()`.

---

## Gap 10: Monitoring & Events (MEDIUM)

**Go reference**: `monitor.go` (4,240) + `events.go` (3,334) + `msgtrace.go` (799) = 8,373 lines
**NET implementation**: `Monitoring/` (1,698) + `Events/` (960) + `MessageTraceContext.cs` = ~2,658 lines
**Gap factor**: 3.1x

### 10.1 Closed Connections Ring Buffer (HIGH)

**Missing**: Ring buffer for recently closed connections with disconnect reasons. `/connz?state=closed` returns empty.

### 10.2 Account-Scoped Filtering (MEDIUM)

**Missing**: `/connz?acc=ACCOUNT` filtering.

### 10.3 Sort Options (MEDIUM)

**Missing**: `ConnzOptions.SortBy` (by bytes, msgs, uptime, etc.).

### 10.4 Message Trace Propagation (MEDIUM)

`MessageTraceContext` exists but trace data not propagated across servers in events.

### 10.5 Auth Error Events (MEDIUM)

**Missing**: `sendAuthErrorEvent()`, `sendAccountAuthErrorEvent()` — cannot monitor auth failures.

### 10.6 Full System Event Payloads (MEDIUM)

Event types defined but payloads may be incomplete (server info, client info fields).

### 10.7 Closed Connection Reason Tracking (MEDIUM)

`ClosedClient.Reason` exists but not populated consistently.

### 10.8 Remote Server Events (LOW)

**Missing**: `remoteServerShutdown()`, `remoteServerUpdate()`, `leafNodeConnected()` — limited cluster member visibility.

### 10.9 Event Compression (LOW)

**Missing**: `getAcceptEncoding()` — system events consume more bandwidth.

### 10.10 OCSP Peer Events (LOW)

**Missing**: `sendOCSPPeerRejectEvent()`, `sendOCSPPeerChainlinkInvalidEvent()`.

---

## Gap 11: Gateway Bridging (MEDIUM)

**Go reference**: `gateway.go` — 3,426 lines
**NET implementation**: `GatewayManager.cs` (225) + `GatewayConnection.cs` (259) + `GatewayInterestTracker.cs` (190) + `ReplyMapper.cs` (174)
**Current .NET total**: ~848 lines
**Gap factor**: 4.0x

### 11.1 Implicit Gateway Discovery (HIGH)

**Missing**: `processImplicitGateway()`, `gossipGatewaysToInboundGateway()`, `forwardNewGatewayToLocalCluster()`. All gateways must be explicitly configured.

### 11.2 Gateway Reconnection with Backoff (MEDIUM)

**Missing**: `solicitGateways()`, `reconnectGateway()`, `solicitGateway()` with structured delay/jitter.

### 11.3 Account-Specific Gateway Routes (MEDIUM)

**Missing**: `sendAccountSubsToGateway()` — routes all subscriptions without per-account isolation.

### 11.4 Queue Group Propagation (MEDIUM)

**Missing**: `sendQueueSubsToGateway()` — queue-based load balancing may not work across gateways.

### 11.5 Reply Subject Mapping Cache (MEDIUM)

**Missing**: `trackGWReply()`, `startGWReplyMapExpiration()` — dynamic reply tracking with TTL. Basic `_GR_` prefix exists but no caching.

### 11.6 Gateway Command Protocol (LOW)

**Missing**: `gatewayCmdGossip`, `gatewayCmdAllSubsStart`, `gatewayCmdAllSubsComplete` — no bulk subscription synchronization.

### 11.7 Connection Registration (LOW)

**Missing**: `registerInboundGatewayConnection()`, `registerOutboundGatewayConnection()`, `getRemoteGateway()` — minimal gateway registry.

---

## Gap 12: Leaf Node Connections (MEDIUM)

**Go reference**: `leafnode.go` — 3,470 lines
**NET implementation**: `LeafNodeManager.cs` (328) + `LeafConnection.cs` (284) + `LeafHubSpokeMapper.cs` (121) + `LeafLoopDetector.cs` (35)
**Current .NET total**: ~768 lines
**Gap factor**: 4.5x

### 12.1 TLS Certificate Hot-Reload (MEDIUM)

**Missing**: `updateRemoteLeafNodesTLSConfig()` — TLS cert changes require server restart.

### 12.2 Permission & Account Syncing (MEDIUM)

**Missing**: `sendPermsAndAccountInfo()`, `initLeafNodeSmapAndSendSubs()` — permission changes on hub may not propagate.

### 12.3 Leaf Connection State Validation (MEDIUM)

**Missing**: `remoteLeafNodeStillValid()` — no validation of remote config on reconnect.

### 12.4 JetStream Migration Checks (LOW)

**Missing**: `checkJetStreamMigrate()` — cannot safely migrate leaf JetStream domains.

### 12.5 Leaf Node WebSocket Support (LOW)

**Missing**: Go accepts WebSocket connections for leaf nodes.

### 12.6 Leaf Cluster Registration (LOW)

**Missing**: `registerLeafNodeCluster()`, `hasLeafNodeCluster()` — cannot query leaf topology.

### 12.7 Connection Disable Flag (LOW)

**Missing**: `isLeafConnectDisabled()` — cannot selectively disable leaf solicitation.

---

## Gap 13: Route Clustering (MEDIUM)

**Go reference**: `route.go` — 3,314 lines
**NET implementation**: `RouteManager.cs` (324) + `RouteConnection.cs` (296) + `RouteCompressionCodec.cs` (135)
**Current .NET total**: ~755 lines
**Gap factor**: 4.4x

### 13.1 Implicit Route Discovery (HIGH)

**Missing**: `processImplicitRoute()`, `forwardNewRouteInfoToKnownServers()`. Routes must be explicitly configured.

### 13.2 Account-Specific Dedicated Routes (MEDIUM)

**Missing**: Per-account route pinning for traffic isolation.

### 13.3 Route Pool Size Negotiation (MEDIUM)

**Missing**: Handling heterogeneous clusters with different pool sizes.

### 13.4 Route Hash Storage (LOW)

**Missing**: `storeRouteByHash()`, `getRouteByHash()` for efficient route lookup.

### 13.5 Cluster Split Handling (LOW)

**Missing**: `removeAllRoutesExcept()`, `removeRoute()` — no partition handling.

### 13.6 No-Pool Route Fallback (LOW)

**Missing**: Interoperability with older servers without pool support.

---

## Gap 14: Configuration & Hot Reload (MEDIUM)

**Go reference**: `opts.go` (6,435) + `reload.go` (2,653) = 9,088 lines
**NET implementation**: `ConfigProcessor.cs` (1,438) + `NatsConfLexer.cs` (1,503) + `NatsConfParser.cs` (421) + `ConfigReloader.cs` (526)
**Current .NET total**: ~3,888 lines
**Gap factor**: 2.3x

### 14.1 SIGHUP Signal Handling (HIGH)

**Missing**: Unix signal handler for config reload without restart.

### 14.2 Auth Change Propagation (MEDIUM)

**Missing**: When users/nkeys change, propagate to existing connections.

### 14.3 TLS Certificate Reload (MEDIUM)

**Missing**: Reload certificates for new connections without restart.

### 14.4 Cluster Config Hot Reload (MEDIUM)

**Missing**: Add/remove route URLs, gateway URLs, leaf node URLs at runtime.

### 14.5 Logging Level Changes (LOW)

**Missing**: Debug/trace/logtime changes at runtime.

### 14.6 JetStream Config Changes (LOW)

**Missing**: JetStream option reload.

---

## Gap 15: WebSocket Support (LOW)

**Go reference**: `websocket.go` — 1,550 lines
**NET implementation**: `WebSocket/` — 1,453 lines (7 files)
**Gap factor**: 1.1x

WebSocket support is the most complete subsystem. Compression negotiation (permessage-deflate), JWT auth through WebSocket, and origin checking are all implemented.

### 15.1 WebSocket-Specific TLS (LOW)

Minor TLS configuration differences.

---

## Priority Summary

### Tier 1: Production Blockers (CRITICAL)

1. **FileStore encryption/compression/recovery** (Gap 1) — blocks data security and durability
2. **FileStore missing interface methods** (Gap 1.9) — blocks API completeness
3. **RAFT persistent log** (Gap 8.1) — blocks cluster persistence
4. **RAFT joint consensus** (Gap 8.2) — blocks safe membership changes
5. **JetStream cluster monitoring loop** (Gap 2.1) — blocks distributed JetStream

### Tier 2: Capability Limiters (HIGH)

6. **Consumer delivery loop** (Gap 3.1) — core consumer functionality
7. **Consumer pull request pipeline** (Gap 3.2) — pull consumer correctness
8. **Consumer ack/redelivery** (Gaps 3.3–3.4) — consumer reliability
9. **Stream mirror/source retry** (Gaps 4.1–4.3) — replication reliability
10. **Stream purge with filtering** (Gap 4.5) — operational requirement
11. **Client flush coalescing** (Gap 5.1) — performance
12. **Client stall gate** (Gap 5.2) — backpressure
13. **MQTT JetStream persistence** (Gap 6.1) — MQTT durability
14. **SIGHUP config reload** (Gap 14.1) — operational requirement
15. **Implicit route/gateway discovery** (Gaps 11.1, 13.1) — cluster usability

### Tier 3: Important Features (MEDIUM)

16–40: Account management, monitoring, gateway details, leaf node features, consumer advanced features, etc.

### Tier 4: Nice-to-Have (LOW)

41+: Internal client kinds, election jitter, event compression, etc.

---

## Test Coverage Gap Summary

All 2,937 Go tests have been categorized:
- **2,646 mapped** (90.1%) — have corresponding .NET tests
- **272 not_applicable** (9.3%) — platform-specific or irrelevant
- **19 skipped** (0.6%) — intentionally deferred
- **0 unmapped** — none remaining

The .NET test suite has **5,808 test methods** (expanding to ~6,409 with parameterized `[Theory]` test cases). Of these, **2,485** (42.8%) are linked back to Go test counterparts via the `test_mappings` table (57,289 mapping rows). The remaining 3,323 .NET tests are original — covering areas like unit tests for .NET-specific implementations, additional edge cases, and subsystems that don't have 1:1 Go equivalents.

Many tests validate API contracts against stubs/mocks rather than testing actual distributed behavior. The gap is in test *depth*, not test *count*.