# Subscriptions — Gap Analysis

> This file tracks what has and hasn't been ported from Go to .NET for the **Subscriptions** module.
> See [stillmissing.md](stillmissing.md) for the full LOC comparison across all modules.

## LLM Instructions: How to Analyze This Category

### Step 1: Read the Go Reference Files

Read each Go source file listed below. For every file:

1. Extract all **exported types** (structs, interfaces, type aliases)
2. Extract all **exported methods** on those types (receiver functions)
3. Extract all **exported standalone functions**
4. Note **key constants, enums, and protocol states**
5. Note **important unexported helpers** that implement core logic (functions >20 lines)
6. Pay attention to **concurrency patterns** (goroutines, mutexes, channels) — these map to different .NET patterns

### Step 2: Read the .NET Implementation Files

Read all `.cs` files in the .NET directories listed below. For each Go symbol found in Step 1:

1. Search for a matching type, method, or function in .NET
2. If found, compare the behavior: does it handle the same edge cases? Same error paths?
3. If partially implemented, note what's missing
4. If not found, note it as MISSING

### Step 3: Cross-Reference Tests

Compare Go test functions against .NET test methods:

1. For each Go `Test*` function, check if a corresponding .NET `[Fact]` or `[Theory]` exists
2. Note which test scenarios are covered and which are missing
3. Check the parity DB (`docs/test_parity.db`) for existing mappings:
   ```bash
   sqlite3 docs/test_parity.db "SELECT go_test, dotnet_test, confidence FROM test_mappings tm JOIN go_tests gt ON tm.go_test_id=gt.rowid JOIN dotnet_tests dt ON tm.dotnet_test_id=dt.rowid WHERE gt.go_file LIKE '%PATTERN%'"
   ```

### Step 4: Classify Each Item

Use these status values:

| Status | Meaning |
|--------|---------|
| **PORTED** | Equivalent exists in .NET with matching behavior |
| **PARTIAL** | .NET implementation exists but is incomplete (missing edge cases, error handling, or features) |
| **MISSING** | No .NET equivalent found — needs to be ported |
| **NOT_APPLICABLE** | Go-specific pattern that doesn't apply to .NET (build tags, platform-specific goroutine tricks, etc.) |
| **DEFERRED** | Intentionally skipped for now (document why) |

### Step 5: Fill In the Gap Inventory

Add rows to the Gap Inventory table below. Group by Go source file. Include the Go file and line number so a porting LLM can jump directly to the reference implementation.

### Key Porting Notes for Subscriptions

- The `Sublist` trie is **performance-critical** — every published message triggers a `Match()` call.
- Cache invalidation uses atomic generation counters (`Interlocked` in .NET).
- `subject_transform.go` handles subject mapping for imports/exports — check if the .NET `Imports/` directory covers this.

---

## Go Reference Files (Source)

- `golang/nats-server/server/sublist.go` — Trie-based subject matcher with wildcard support (`*` single, `>` multi). Nodes have `psubs` (plain), `qsubs` (queue groups). Results cached with atomic generation IDs.
- `golang/nats-server/server/subject_transform.go` — Subject transformation logic (mapping, filtering)

## Go Reference Files (Tests)

- `golang/nats-server/server/sublist_test.go`
- `golang/nats-server/server/subject_transform_test.go`

## .NET Implementation Files (Source)

- `src/NATS.Server/Subscriptions/SubjectMatch.cs`
- `src/NATS.Server/Subscriptions/SubList.cs`
- `src/NATS.Server/Subscriptions/SubListResult.cs`
- `src/NATS.Server/Subscriptions/Subscription.cs`
- All other files in `src/NATS.Server/Subscriptions/`

## .NET Implementation Files (Tests)

- `tests/NATS.Server.Tests/Subscriptions/`
- `tests/NATS.Server.Tests/SubList/`

---

## Gap Inventory

<!-- After analysis, fill in this table. Group rows by Go source file. -->

### golang/nats-server/server/sublist.go

| Go Symbol | Go File:Line | Status | .NET Equivalent | Notes |
|-----------|:-------------|--------|:----------------|-------|
| `SublistResult` (struct) | sublist.go:59 | PORTED | `src/NATS.Server/Subscriptions/SubListResult.cs:4` | Fields renamed: `psubs`→`PlainSubs`, `qsubs`→`QueueSubs`; .NET uses arrays instead of slices |
| `Sublist` (struct) | sublist.go:65 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:11` | Core trie struct ported; notification model differs (event vs channels) |
| `notifyMaps` (struct) | sublist.go:80 | NOT_APPLICABLE | — | Go uses buffered channels for interest notifications; .NET uses `InterestChanged` event (`InterestChange.cs`) |
| `node` (struct) | sublist.go:87 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:974` (private `TrieNode`) | Inner class; `psubs`+`plist` merged into `PlainSubs HashSet`, `qsubs`→`QueueSubs Dictionary` |
| `level` (struct) | sublist.go:96 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:967` (private `TrieLevel`) | Inner class; `nodes`, `pwc`, `fwc` all present |
| `newNode()` | sublist.go:102 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:974` | Inline `new TrieNode()` |
| `newLevel()` | sublist.go:107 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:967` | Inline `new TrieLevel()` |
| `NewSublist(bool)` | sublist.go:117 | PARTIAL | `src/NATS.Server/Subscriptions/SubList.cs:11` | .NET `SubList` always starts with cache; no `enableCache` constructor param |
| `NewSublistWithCache()` | sublist.go:125 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:11` | Default `new SubList()` has cache enabled |
| `NewSublistNoCache()` | sublist.go:130 | MISSING | — | No .NET equivalent; SubList always caches |
| `CacheEnabled()` | sublist.go:135 | MISSING | — | No public method to query whether cache is on; `CacheCount` exists but different semantics |
| `RegisterNotification()` | sublist.go:149 | MISSING | — | Go sends `true/false` on channel when first/last interest added/removed; .NET uses `InterestChanged` event which fires on every change but doesn't replicate channel-based deferred notify semantics |
| `RegisterQueueNotification()` | sublist.go:153 | MISSING | — | Queue-specific interest notification; no .NET equivalent |
| `ClearNotification()` | sublist.go:227 | MISSING | — | No .NET equivalent for removing a notification channel |
| `ClearQueueNotification()` | sublist.go:231 | MISSING | — | No .NET equivalent |
| `chkForInsertNotification()` | sublist.go:301 | NOT_APPLICABLE | — | Internal helper for channel notification; replaced by `InterestChanged` event emission in `Insert()` |
| `chkForRemoveNotification()` | sublist.go:317 | NOT_APPLICABLE | — | Internal helper; replaced by `InterestChanged` event emission in `Remove()` |
| `sendNotification()` | sublist.go:253 | NOT_APPLICABLE | — | Non-blocking channel send; Go-specific pattern, no .NET equivalent needed |
| `addInsertNotify()` | sublist.go:262 | NOT_APPLICABLE | — | Internal channel registration helper; replaced by event model |
| `addRemoveNotify()` | sublist.go:268 | NOT_APPLICABLE | — | Internal channel registration helper |
| `addNotify()` | sublist.go:274 | NOT_APPLICABLE | — | Internal channel map helper |
| `keyFromSubjectAndQueue()` | sublist.go:290 | NOT_APPLICABLE | — | Key generation for notification maps; not needed in .NET event model |
| `Insert()` | sublist.go:356 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:179` | Full trie insertion with queue support; fires `InterestChanged` event instead of channel notify |
| `copyResult()` | sublist.go:449 | NOT_APPLICABLE | — | Go uses copy-on-write for cache mutation; .NET creates new `SubListResult` directly |
| `SublistResult.addSubToResult()` | sublist.go:460 | NOT_APPLICABLE | — | Copy-on-write pattern for cache updates; not needed in .NET generation-based cache invalidation |
| `addToCache()` | sublist.go:478 | NOT_APPLICABLE | — | Go updates individual cache entries on insert; .NET uses generation-based invalidation (simpler) |
| `removeFromCache()` | sublist.go:498 | NOT_APPLICABLE | — | Same as above; .NET bumps generation counter instead |
| `Match()` | sublist.go:520 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:360` | Generation-based cache; same algorithm |
| `MatchBytes()` | sublist.go:526 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:425` | Takes `ReadOnlySpan<byte>` vs `[]byte` |
| `HasInterest()` | sublist.go:532 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:638` | Cache-aware fast path |
| `NumInterest()` | sublist.go:537 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:669` | Returns `(plainCount, queueCount)` tuple |
| `matchNoLock()` | sublist.go:543 | NOT_APPLICABLE | — | Internal; .NET lock model differs (no equivalent needed) |
| `match()` | sublist.go:547 | NOT_APPLICABLE | — | Internal implementation; split into `Match()` + private helpers in .NET |
| `hasInterest()` | sublist.go:624 | NOT_APPLICABLE | — | Internal; maps to `HasInterestLevel()` private helper |
| `reduceCacheCount()` | sublist.go:675 | PORTED | `src/NATS.Server/Subscriptions/SubListCacheSweeper.cs:7` + `SubList.cs:458` | Background goroutine mapped to `SubListCacheSweeper` + `SweepCache()` |
| `isRemoteQSub()` | sublist.go:689 | NOT_APPLICABLE | — | Go has client.kind == ROUTER/LEAF; .NET uses `RemoteSubscription` model instead |
| `UpdateRemoteQSub()` | sublist.go:695 | MISSING | — | Go updates weight of remote qsub; .NET uses `ApplyRemoteSub()` for a different model (full add/remove) |
| `addNodeToResults()` | sublist.go:706 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:549` (private `AddNodeToResults()`) | Remote qsub weight expansion present in Go missing in .NET |
| `findQSlot()` | sublist.go:745 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:562` (inline in `AddNodeToResults`) | Inlined in .NET |
| `matchLevel()` | sublist.go:757 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:506` (private `MatchLevel()`) | Core trie descent algorithm |
| `matchLevelForAny()` | sublist.go:785 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:754` (private `HasInterestLevel()`) + `CountInterestLevel()` | Split into two .NET helpers |
| `remove()` (internal) | sublist.go:843 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:282` (private `RemoveInternal()`) | Internal removal logic |
| `Remove()` | sublist.go:915 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:255` | Fires `InterestChanged` event |
| `RemoveBatch()` | sublist.go:920 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:687` | Cache disable/re-enable pattern ported |
| `level.pruneNode()` | sublist.go:953 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:345` (inline in `RemoveInternal`) | Inlined in removal path |
| `node.isEmpty()` | sublist.go:968 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:981` (`TrieNode.IsEmpty` property) | Property instead of method |
| `level.numNodes()` | sublist.go:978 | NOT_APPLICABLE | — | Used internally in `visitLevel()`; no .NET equivalent needed |
| `removeFromNode()` | sublist.go:993 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:324` (inline in `RemoveInternal`) | Inlined |
| `Count()` | sublist.go:1023 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:41` (`Count` property) | |
| `CacheCount()` | sublist.go:1030 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:97` (`CacheCount` property) | |
| `SublistStats` (struct) | sublist.go:1038 | PORTED | `src/NATS.Server/Subscriptions/SubListStats.cs:3` | All public fields present; unexported fields `totFanout`, `cacheCnt`, `cacheHits` dropped (computed inline in `Stats()`) |
| `SublistStats.add()` | sublist.go:1052 | MISSING | — | Aggregates multiple SublistStats into one; used for cluster monitoring; no .NET equivalent |
| `Stats()` | sublist.go:1076 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:580` | Full fanout stats computed |
| `numLevels()` | sublist.go:1120 | MISSING | — | Debug/test utility counting trie depth; not ported |
| `visitLevel()` | sublist.go:1126 | MISSING | — | Internal helper for `numLevels()`; not ported |
| `subjectHasWildcard()` | sublist.go:1159 | PARTIAL | `src/NATS.Server/Subscriptions/SubjectMatch.cs:50` (`IsLiteral()` — inverse) | .NET `!IsLiteral()` is equivalent but not a dedicated function |
| `subjectIsLiteral()` | sublist.go:1174 | PORTED | `src/NATS.Server/Subscriptions/SubjectMatch.cs:50` (`IsLiteral()`) | Exact equivalent |
| `IsValidPublishSubject()` | sublist.go:1187 | PORTED | `src/NATS.Server/Subscriptions/SubjectMatch.cs:67` | |
| `IsValidSubject()` | sublist.go:1192 | PORTED | `src/NATS.Server/Subscriptions/SubjectMatch.cs:9` | |
| `isValidSubject()` (internal, checkRunes) | sublist.go:1196 | PORTED | `src/NATS.Server/Subscriptions/SubjectMatch.cs:211` (`IsValidSubject(string, bool)`) | |
| `IsValidLiteralSubject()` | sublist.go:1236 | PARTIAL | `src/NATS.Server/Subscriptions/SubjectMatch.cs:50` (`IsLiteral()`) | `IsLiteral()` does not validate the subject first; `IsValidPublishSubject()` combines both |
| `isValidLiteralSubject()` (tokens iter) | sublist.go:1241 | NOT_APPLICABLE | — | Takes `iter.Seq[string]` (Go 1.23 iterator); C# uses different iteration model |
| `ValidateMapping()` | sublist.go:1258 | MISSING | — | Validates a mapping destination subject string including `{{function()}}` syntax; no public .NET equivalent |
| `analyzeTokens()` | sublist.go:1298 | NOT_APPLICABLE | — | Internal helper used only in `SubjectsCollide()`; logic inlined in .NET `SubjectsCollide()` |
| `tokensCanMatch()` | sublist.go:1314 | PORTED | `src/NATS.Server/Subscriptions/SubjectMatch.cs:199` (private `TokensCanMatch()`) | |
| `SubjectsCollide()` | sublist.go:1326 | PORTED | `src/NATS.Server/Subscriptions/SubjectMatch.cs:159` | |
| `numTokens()` | sublist.go:1374 | PORTED | `src/NATS.Server/Subscriptions/SubjectMatch.cs:118` (`NumTokens()`) | |
| `tokenAt()` | sublist.go:1389 | PORTED | `src/NATS.Server/Subscriptions/SubjectMatch.cs:132` (`TokenAt()`) | Go is 1-based index; .NET is 0-based |
| `tokenizeSubjectIntoSlice()` | sublist.go:1407 | NOT_APPLICABLE | — | Internal slice-reuse helper; .NET uses `Tokenize()` private method in SubList |
| `SubjectMatchesFilter()` | sublist.go:1421 | PARTIAL | `src/NATS.Server/JetStream/Storage/MemStore.cs:1175` (private), `FileStore.cs:773` (private) | Duplicated as private methods in MemStore and FileStore; not a public standalone function |
| `subjectIsSubsetMatch()` | sublist.go:1426 | MISSING | — | No public .NET equivalent; logic exists privately in MemStore/FileStore |
| `isSubsetMatch()` | sublist.go:1434 | MISSING | — | Internal; no public .NET equivalent |
| `isSubsetMatchTokenized()` | sublist.go:1444 | MISSING | — | Internal; no public .NET equivalent |
| `matchLiteral()` | sublist.go:1483 | PORTED | `src/NATS.Server/Subscriptions/SubjectMatch.cs:75` (`MatchLiteral()`) | |
| `addLocalSub()` | sublist.go:1552 | NOT_APPLICABLE | — | Filters by client kind (CLIENT/SYSTEM/JETSTREAM/ACCOUNT/LEAF); no .NET equivalent needed (client kind routing done elsewhere) |
| `Sublist.addNodeToSubs()` | sublist.go:1562 | NOT_APPLICABLE | — | Internal helper for `localSubs()`; not ported |
| `Sublist.collectLocalSubs()` | sublist.go:1581 | NOT_APPLICABLE | — | Internal helper for `localSubs()`; not ported |
| `Sublist.localSubs()` | sublist.go:1597 | MISSING | — | Returns only local-client subscriptions (excludes routes/gateways); no .NET equivalent |
| `Sublist.All()` | sublist.go:1604 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:712` | |
| `Sublist.addAllNodeToSubs()` | sublist.go:1610 | NOT_APPLICABLE | — | Internal helper for `All()`; inlined in .NET |
| `Sublist.collectAllSubs()` | sublist.go:1627 | NOT_APPLICABLE | — | Internal; inlined in `CollectAllSubs()` private method in .NET |
| `ReverseMatch()` | sublist.go:1649 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:727` | |
| `reverseMatchLevel()` | sublist.go:1674 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:860` (private `ReverseMatchLevel()`) | |
| `getAllNodes()` | sublist.go:1714 | PORTED | `src/NATS.Server/Subscriptions/SubList.cs:909` (private `CollectAllNodes()`) | |

### golang/nats-server/server/subject_transform.go

| Go Symbol | Go File:Line | Status | .NET Equivalent | Notes |
|-----------|:-------------|--------|:----------------|-------|
| Transform type constants (`NoTransform`…`Random`) | subject_transform.go:43 | PARTIAL | `src/NATS.Server/Subscriptions/SubjectTransform.cs:682` (private `TransformType` enum) | `Random` (value 11 in Go) is absent from the .NET enum and switch statement; all others ported |
| `subjectTransform` (struct) | subject_transform.go:61 | PORTED | `src/NATS.Server/Subscriptions/SubjectTransform.cs:11` | Internal fields mapped to `_source`, `_dest`, `_sourceTokens`, `_destTokens`, `_ops` |
| `SubjectTransformer` (interface) | subject_transform.go:73 | NOT_APPLICABLE | — | Go exports interface for polymorphism; C# uses concrete `SubjectTransform` class directly |
| `NewSubjectTransformWithStrict()` | subject_transform.go:81 | MISSING | — | Strict mode validates that all source wildcards are used in dest; no .NET equivalent |
| `NewSubjectTransform()` | subject_transform.go:198 | PORTED | `src/NATS.Server/Subscriptions/SubjectTransform.cs:31` (`Create()`) | Non-strict creation |
| `NewSubjectTransformStrict()` | subject_transform.go:202 | MISSING | — | Strict version for import mappings; no .NET equivalent |
| `getMappingFunctionArgs()` | subject_transform.go:206 | PORTED | `src/NATS.Server/Subscriptions/SubjectTransform.cs:639` (private `GetFunctionArgs()`) | |
| `transformIndexIntArgsHelper()` | subject_transform.go:215 | PORTED | `src/NATS.Server/Subscriptions/SubjectTransform.cs:610` (private `ParseIndexIntArgs()`) | |
| `indexPlaceHolders()` | subject_transform.go:237 | PORTED | `src/NATS.Server/Subscriptions/SubjectTransform.cs:486` (`ParseDestToken()` + `ParseMustacheToken()`) | Split into two methods; `Random` branch missing |
| `transformTokenize()` | subject_transform.go:378 | MISSING | — | Converts `foo.*.*` to `foo.$1.$2`; used for import subject mapping reversal; no .NET equivalent |
| `transformUntokenize()` | subject_transform.go:399 | MISSING | — | Inverse of above; used in `reverse()`; no .NET equivalent |
| `tokenizeSubject()` | subject_transform.go:414 | NOT_APPLICABLE | — | Internal tokenizer; .NET uses `string.Split('.')` or `Tokenize()` private method |
| `subjectTransform.Match()` | subject_transform.go:433 | PORTED | `src/NATS.Server/Subscriptions/SubjectTransform.cs:126` (`Apply()`) | Renamed; returns `null` instead of error on no-match |
| `subjectTransform.TransformSubject()` | subject_transform.go:456 | PARTIAL | `src/NATS.Server/Subscriptions/SubjectTransform.cs:126` (via `Apply()`) | `TransformSubject` (apply without match check) not separately exposed; `Apply()` always checks match |
| `subjectTransform.getRandomPartition()` | subject_transform.go:460 | MISSING | — | `Random` transform type not implemented in .NET |
| `subjectTransform.getHashPartition()` | subject_transform.go:469 | PORTED | `src/NATS.Server/Subscriptions/SubjectTransform.cs:226` (`ComputePartition()` + `Fnv1A32()`) | FNV-1a 32-bit hash ported |
| `subjectTransform.TransformTokenizedSubject()` | subject_transform.go:482 | PORTED | `src/NATS.Server/Subscriptions/SubjectTransform.cs:144` (private `TransformTokenized()`) | All transform types except `Random` ported |
| `subjectTransform.reverse()` | subject_transform.go:638 | MISSING | — | Produces the inverse transform; used for import subject mapping; no .NET equivalent |
| `subjectInfo()` | subject_transform.go:666 | PORTED | `src/NATS.Server/Subscriptions/SubjectTransform.cs:451` (private `SubjectInfo()`) | |
| `ValidateMapping()` (in subject_transform.go context) | sublist.go:1258 | MISSING | — | Also defined via `NewSubjectTransform`; validates mapping destination with function syntax; no .NET public equivalent |

---

## Keeping This File Updated

After porting work is completed:

1. **Update status**: Change `MISSING → PORTED` or `PARTIAL → PORTED` for each item completed
2. **Add .NET path**: Fill in the ".NET Equivalent" column with the actual file:line
3. **Re-count LOC**: Update the LOC numbers in `stillmissing.md`:
   ```bash
   # Re-count .NET source LOC for this module
   find src/NATS.Server/Subscriptions/ -name '*.cs' -type f -exec cat {} + | wc -l
   # Re-count .NET test LOC for this module
   find tests/NATS.Server.Tests/Subscriptions/ tests/NATS.Server.Tests/SubList/ -name '*.cs' -type f -exec cat {} + | wc -l
   ```
4. **Add a changelog entry** below with date and summary of what was ported
5. **Update the parity DB** if new test mappings were created:
   ```bash
   sqlite3 docs/test_parity.db "INSERT INTO test_mappings (go_test_id, dotnet_test_id, confidence, notes) VALUES (?, ?, 'manual', 'ported in YYYY-MM-DD session')"
   ```

## Change Log

| Date | Change | By |
|------|--------|----|
| 2026-02-25 | File created with LLM analysis instructions | auto |
| 2026-02-25 | Full gap inventory populated: analyzed sublist.go (~1,729 lines) and subject_transform.go (~689 lines) against all .NET Subscriptions/*.cs files. Counted 49 PORTED, 6 PARTIAL, 22 MISSING, 27 NOT_APPLICABLE, 0 DEFERRED. | claude-sonnet-4-6 |