jormun-db/TODO.md

# JormunDB (Odin rewrite) — TODO

This tracks the rewrite from Zig (ZynamoDB) → Odin (JormunDB), and what's left to stabilize + extend.

## Status Snapshot

### ✅ Ported / Working (core)
- [x] Project layout + Makefile targets (build/run/test/fmt)
- [x] RocksDB bindings / integration
- [x] Core DynamoDB types (AttributeValue / Item / Key / TableDescription, etc.)
- [x] Binary key codec (varint length-prefixed segments)
- [x] Binary item codec (TLV encoding / decoding)
- [x] Storage engine: tables + CRUD + scan/query plumbing
- [x] Table-level RW locks (read ops shared / write ops exclusive)
- [x] HTTP server + request routing via `X-Amz-Target`
- [x] DynamoDB JSON (parse + serialize)
- [x] Expression parsing for Query key conditions (basic support)

---

## Now (MVP correctness + polish)
Goal: "aws cli works reliably for CreateTable/ListTables/PutItem/GetItem/DeleteItem/Scan/Query" with correct DynamoDB-ish responses.

### 1) HTTP + routing hardening
- [ ] Audit request parsing boundaries:
  - Max body size enforcement (config exists, need to verify enforcement path)
  - Missing/invalid headers → correct DynamoDB error types
  - Content-Type handling (be permissive but consistent)
- [x] Ensure **all request-scoped allocations** come from the request arena (no accidental long-lived allocs)
  - Verified: `handle_connection` in http.odin sets `context.allocator = request_alloc`
  - Long-lived data (table metadata, locks) explicitly uses `engine.allocator`
- [x] Standardize error responses:
  - `__type` formatting — done, uses `com.amazonaws.dynamodb.v20120810#ErrorType`
  - `message` field consistency — done
  - Status code mapping per error type — **DONE**: centralized `handle_storage_error` + `make_error_response` now maps InternalServerError→500, everything else→400
  - Missing X-Amz-Target now returns `SerializationException` (matches real DynamoDB)

### 2) Storage correctness edge cases
- [x] Table metadata durability + validation:
  - [x] Reject duplicate tables — done in `create_table` (checks existing meta key)
  - [x] Reject invalid key schema — done in `parse_key_schema` (no HASH, multiple HASH, etc.)
- [x] Item validation against key schema:
  - [x] Missing PK/SK errors — done in `key_from_item`
  - [x] Type mismatch errors (S/N/B) — **DONE**: new `validate_item_key_types` proc checks item key attr types against AttributeDefinitions
- [ ] Deterministic encoding tests:
  - [ ] Key codec round-trip
  - [ ] TLV item encode/decode round-trip (nested maps/lists/sets)

### 3) Query/Scan pagination parity
- [x] Make pagination behavior match AWS CLI expectations:
  - [x] `Limit` — done
  - [x] `ExclusiveStartKey` — done (parsed via JSON object lookup with key schema type reconstruction)
  - [x] `LastEvaluatedKey` generation — **FIXED**: now saves key of *last returned item* (not next unread item); only emits when more results exist
- [ ] Add "golden" pagination tests:
  - [ ] Query w/ sort key ranges
  - [ ] Scan limit + resume loop

### 4) Expression parsing reliability
- [x] Remove brittle string-scanning for `KeyConditionExpression` extraction:
  - **DONE**: `parse_key_condition_expression_string` uses JSON object lookup (handles whitespace/ordering safely)
- [ ] Add validation + better errors for malformed expressions
- [x] Expand operator coverage: BETWEEN and begins_with are implemented in parser
- [x] **Sort key condition filtering in query** — **DONE**: `query()` now accepts optional `Sort_Key_Condition` and applies it (=, <, <=, >, >=, BETWEEN, begins_with)

---

## Next (feature parity with Zig + API completeness)
### 5) UpdateItem / conditional logic groundwork
- [x] `UpdateItem` handler registered in router (currently returns clear "not yet supported" error)
- [x] Implement `UpdateItem` (initially minimal: SET for scalar attrs)
- [ ] Add `ConditionExpression` support for Put/Delete/Update (start with simple comparisons)
- [x] Define internal "update plan" representation (parsed ops → applied mutations)

### 6) Response completeness / options
- [x] `ReturnValues` handling where relevant (NONE/ALL_OLD/UPDATED_NEW etc. — even partial support is useful)
- [x] `ProjectionExpression` (return subset of attributes)
- [x] `FilterExpression` (post-query filter for Scan/Query)

### 7) Test coverage / tooling
- [ ] Add integration tests mirroring AWS CLI script flows:
  - create table → put → get → scan → query → delete
- [ ] Add fuzz-ish tests for:
  - JSON parsing robustness
  - expression parsing robustness
  - TLV decode failure cases (corrupt bytes)

---

## Bug Fixes Applied This Session

### Pagination (scan + query)
**Bug**: `last_evaluated_key` was set to the key of the *next unread* item (the item at `count == limit`). When the client resumed with that key as `ExclusiveStartKey`, it would seek-then-skip, **dropping one item** from the result set.

**Fix**: Now tracks the key of the *last successfully returned* item. Only emits `LastEvaluatedKey` when we confirm there are more items beyond the returned set (via `has_more` flag).

### Sort key condition filtering
**Bug**: `query()` performed a partition-prefix scan but never applied the sort key condition (=, <, BETWEEN, begins_with, etc.) from `KeyConditionExpression`. All items in the partition were returned regardless of sort key predicates.

**Fix**: `query()` now accepts an optional `Sort_Key_Condition` parameter. The handler extracts it from the parsed `Key_Condition` and passes it through. `evaluate_sort_key_condition()` compares the item's SK attribute against the condition using string comparison (matching DynamoDB's lexicographic semantics for S/N/B keys).

### Write locking
**Bug**: `put_item` and `delete_item` acquired *shared* (read) locks. Multiple concurrent writes to the same table could interleave without mutual exclusion.

**Fix**: Both now acquire *exclusive* (write) locks via `sync.rw_mutex_lock`. Read operations (`get_item`, `scan`, `query`) continue to use shared locks.

### delete_table item cleanup
**Bug**: `delete_table` only deleted the metadata key, leaving all data items orphaned in RocksDB.

**Fix**: Before deleting metadata, `delete_table` now iterates over all keys with the table's data prefix and deletes them individually.

### Item key type validation
**New**: `put_item` now validates that the item's key attribute types match the table's `AttributeDefinitions`. E.g., if PK is declared as `S`, putting an item with a numeric PK is rejected with `Invalid_Key`.

### Error response standardization
**Fix**: Centralized all storage-error-to-HTTP-error mapping in `handle_storage_error`. InternalServerError maps to HTTP 500; all client errors (validation, not-found, etc.) map to HTTP 400. Missing `X-Amz-Target` now returns `SerializationException` to match real DynamoDB behavior.

---

## Later (big features)
These align with the "Future Enhancements" list in ARCHITECTURE.md.

### 8) Secondary indexes
- [ ] Global Secondary Indexes (GSI)
- [ ] Local Secondary Indexes (LSI)
- [ ] Index backfill + write-path maintenance

### 9) Batch + transactions
- [ ] BatchWriteItem
- [ ] BatchGetItem
- [ ] Transactions (TransactWriteItems / TransactGetItems)

### 10) Performance / ops
- [ ] Connection reuse / keep-alive tuning
- [ ] Bloom filters / RocksDB options tuning for common patterns
- [ ] Optional compression policy (LZ4/Zstd knobs)
- [ ] Parallel scan (segment scanning)

---

## Replication / WAL
(There is a C++ shim stubbed out for WAL iteration and applying write batches.)
- [ ] Implement WAL iterator: `latest_sequence`, `wal_iter_next` returning writebatch blob
- [ ] Implement apply-writebatch on follower
- [ ] Add a minimal replication test harness (leader generates N ops → follower applies → compare)

---

## Housekeeping
- [x] Fix TODO hygiene: keep this file short and "actionable"
  - Added "Bug Fixes Applied" section documenting what changed and why
- [ ] Add a CONTRIBUTING quick checklist (allocator rules, formatting, tests)
- [ ] Add "known limitations" section in README (unsupported DynamoDB features)