seaweedfs/weed/mq/kafka/IMPLEMENTATION_PHASES.md

Kafka Gateway Implementation Phases

Phase 1: Core SeaweedMQ Integration (COMPLETED ✅)

Goal: Enable real message retrieval from SeaweedMQ storage

Tasks:

• Implement integration.SeaweedMQHandler.GetStoredRecords() to return actual records
• Add proper SMQ record conversion from SeaweedMQ format to Kafka format
• Wire Fetch API to use real SMQ records instead of synthetic batches
• Add integration tests for end-to-end message storage and retrieval

Files modified:

• weed/mq/kafka/integration/seaweedmq_handler.go
• weed/mq/kafka/protocol/fetch.go (verification)
• Added test file: weed/mq/kafka/integration/record_retrieval_test.go

Verification: E2E tests show "Found X SMQ records" - real data retrieval working

Phase 2: CreateTopics Protocol Compliance (COMPLETED ✅)

Goal: Fix CreateTopics API parsing and partition handling

Tasks:

• Implement handleCreateTopicsV0V1 request parsing
• Add support for partition count and basic topic configurations
• Wire CreateTopics to actual SeaweedMQ topic creation
• Add CreateTopics integration tests

Files modified:

• weed/mq/kafka/protocol/handler.go
• Added test file: weed/mq/kafka/protocol/create_topics_test.go

Verification: All v0-v5 CreateTopics tests pass; proper partition handling

Phase 3: ApiVersions Matrix Accuracy (COMPLETED ✅)

Goal: Ensure advertised API versions match actual implementation

Tasks:

• Audit current handleApiVersions response against implemented features
• Correct max versions for APIs with higher implementations than advertised
• Update version validation in request handlers to match advertisements
• Document supported vs unsupported features per API version

Files modified:

• weed/mq/kafka/protocol/handler.go (handleApiVersions & validateAPIVersion)
• Added file: weed/mq/kafka/API_VERSION_MATRIX.md
• Added test file: weed/mq/kafka/protocol/api_versions_test.go

Verification: Critical fixes for OffsetFetch v0-v5 and CreateTopics v0-v5 accuracy

Phase 4: Consumer Group Protocol Metadata (COMPLETED ✅)

Goal: Proper JoinGroup protocol metadata parsing

Tasks:

• Implement consumer protocol metadata parsing in JoinGroup
• Extract subscription topics and user data from metadata
• Populate ClientHost from connection information
• Support multiple assignment strategies properly

Files modified:

• weed/mq/kafka/protocol/joingroup.go
• weed/mq/kafka/protocol/handler.go (connection context)
• Added file: weed/mq/kafka/protocol/consumer_group_metadata.go
• Added test file: weed/mq/kafka/protocol/consumer_group_metadata_test.go

Verification: ClientHost shows real IPs; enhanced protocol metadata parsing with 17 tests

Phase 5: Multi-Batch Fetch Support (COMPLETED ✅)

Goal: Support multiple record batch concatenation in Fetch responses

Tasks:

• Implement proper record batch concatenation
• Handle batch size limits and chunking
• Add support for compressed record batches
• Performance optimization for large batch responses

Files modified:

• weed/mq/kafka/protocol/fetch.go (integrated multi-batch fetcher)
• Added file: weed/mq/kafka/protocol/fetch_multibatch.go
• Added test file: weed/mq/kafka/protocol/fetch_multibatch_test.go

Verification: MaxBytes compliance, multi-batch concatenation, 17 comprehensive tests, E2E compatibility

Phase 6: Basic Flexible Versions Support (COMPLETED ✅)

Goal: Basic support for flexible versions and tagged fields

Tasks:

• Add flexible version detection in request headers
• Implement tagged field parsing/skipping (with backward compatibility)
• Update response encoders for flexible versions (ApiVersions v3+)
• Add flexible version tests

Files modified:

• weed/mq/kafka/protocol/handler.go (added header parsing with fallback)
• Added file: weed/mq/kafka/protocol/flexible_versions.go
• Added test file: weed/mq/kafka/protocol/flexible_versions_test.go
• Added test file: weed/mq/kafka/protocol/flexible_versions_integration_test.go

Verification: 27 flexible version tests pass; robust fallback for older clients; E2E compatibility maintained

Phase 7: Comprehensive Error Handling and Edge Cases (COMPLETED ✅)

Goal: Comprehensive error handling and Kafka spec compliance

Tasks:

• Audit all error codes against Kafka specification
• Add missing error codes for network/timeout scenarios
• Implement proper connection timeout handling
• Add comprehensive error handling tests

Files modified:

• Added file: weed/mq/kafka/protocol/errors.go (centralized error codes)
• Added test file: weed/mq/kafka/protocol/error_handling_test.go
• weed/mq/kafka/protocol/handler.go (enhanced timeout handling)
• Updated all protocol handlers to use centralized error codes

Verification: 21 error handling tests pass; unified error code usage; robust timeout detection; E2E compatibility maintained

Current Status: All Phases 1-7 completed! ✅

Implementation Summary:

• Complete Kafka protocol gateway with SeaweedMQ integration
• All major APIs implemented (Produce, Fetch, CreateTopics, Consumer Groups, Metadata, etc.)
• Multi-batch fetch support with MaxBytes compliance
• Flexible version support for modern Kafka clients
• Comprehensive error handling and timeout management
• Extensive test coverage with 100+ tests across all components
• Full E2E compatibility with Sarama and kafka-go clients

Implementation Notes:

• Each phase should include comprehensive tests
• Commit after each phase completion
• Backward compatibility must be maintained
• Integration tests should verify end-to-end functionality