| # CROSS3: Protocol Bridge — JSON to Message Translation |
|
|
| ## Goal |
| Fix 4 translation bugs and 2 error mapping bugs in the bridge service that translates |
| Service A's JSON REST API responses into structured messages for Service B's consumer. |
|
|
| ## Requirements |
| 1. int64 fields must be translated as Python int (no truncation to 32-bit) |
| 2. bytes fields must be base64-decoded from JSON strings |
| 3. oneof fields must have exactly one variant set (not multiple) |
| 4. enum fields must be mapped from string names to integer values |
| 5. HTTP 404 from Service A must map to NOT_FOUND error code (5) for Service B |
| 6. HTTP 429 from Service A must map to RESOURCE_EXHAUSTED error code (8) for Service B |
| 7. All tests must pass: `pytest tests/` |
|
|
| ## Supporting Documents |
| - `service_a/models.py` — JSON data models from Service A |
| - `service_b/schema.py` — Message schema for Service B (proto3-style) |
| - `bridge/translator.py` — JSON→Message translation (4 bugs) |
| - `bridge/error_mapper.py` — HTTP status → error code (2 bugs) |
|
|
| ## Background |
|
|
| The bridge service sits between Service A (a REST API returning JSON) and Service B |
| (a queue consumer expecting structured proto3-style messages). Because JSON and proto3 |
| have different type semantics, every field crossing this boundary needs a careful |
| type conversion. |
|
|
| ### Type Semantic Differences |
|
|
| | JSON Type | Proto3 Type | Issue | |
| |-----------|-------------|-------| |
| | number | int64 | JSON numbers lose precision for values > 2^53; must not be masked to 32-bit | |
| | string | bytes | Binary data is base64-encoded in JSON; must be decoded to bytes | |
| | object | oneof | JSON may include multiple keys; proto3 oneof allows exactly one | |
| | string | enum | Enum names in JSON must be converted to integer codes | |
|
|
| ### Error Code Mapping |
|
|
| Service A returns HTTP status codes. Service B uses gRPC-style integer error codes: |
|
|
| | HTTP Status | Expected Error Code | Code Number | |
| |-------------|---------------------|-------------| |
| | 200 | OK | 0 | |
| | 400 | INVALID_ARGUMENT | 3 | |
| | 401/403 | INVALID_ARGUMENT | 3 | |
| | 404 | NOT_FOUND | 5 | |
| | 429 | RESOURCE_EXHAUSTED | 8 | |
| | 5xx | INTERNAL | 13 | |
|
|
| ## Real-World Context |
| JSON-to-gRPC transcoding bridges are a common integration layer in microservice |
| architectures, and the 6 bugs in this task reflect bugs documented in real transcoding |
| implementations: |
| - **int64 truncation (Bug 1)**: JavaScript's `JSON.parse()` silently truncates 64-bit |
| integers beyond `Number.MAX_SAFE_INTEGER` (2^53-1). This caused data loss in the |
| Twitter Snowflake ID migration (2010) and is documented in the gRPC-Gateway project |
| FAQ. Fix: serialize int64 as strings in JSON. |
| - **bytes base64 handling (Bug 2)**: Proto3 `bytes` fields must be base64-encoded in |
| JSON (RFC 4648). The gRPC-Gateway library had exactly this bug in v1.x — binary |
| fields were passed through raw, corrupting payloads. CVE-class issue in several |
| open-source gRPC-JSON bridges. |
| - **oneof variant mapping (Bug 3)**: Proto3 `oneof` fields in JSON use the field name |
| as the key, not the oneof name. Incorrect mapping silently drops the value. |
| - **enum integer vs string (Bug 4)**: Proto3 JSON canonical form uses enum names |
| (strings), not integers. Several gRPC web clients (grpc-web, grpc-gateway) have |
| shipped this mismatch causing 0-value enums for all inputs. |
| - **Error code mapping (Bugs 5–6)**: gRPC status codes (google.rpc.Code) are a |
| strict mapping from HTTP status; 404→NOT_FOUND(5) and 429→RESOURCE_EXHAUSTED(8) |
| are specified in google.rpc.Code and commonly misimplemented. |
|
|
