bun.sh/STATUS.md

HTTP/2 Client Implementation Status

This document provides an honest assessment of the current HTTP/2 client implementation in Bun's fetch API.

Current Implementation Status: EXPERIMENTAL / INCOMPLETE

✅ What Has Been Implemented

Core HTTP/2 Infrastructure

• HTTP/2 Frame Handling: Complete implementation of essential frame types (HEADERS, DATA, SETTINGS, PING, GOAWAY, WINDOW_UPDATE, RST_STREAM)
• HPACK Integration: Uses existing lshpack library for header compression/decompression
• Stream Management: Client-side stream allocation with odd-numbered stream IDs (1, 3, 5, ...)
• Connection Lifecycle: HTTP/2 connection preface, settings exchange, and proper teardown
• Flow Control: Basic implementation of connection and stream-level flow control

Integration Points

• HTTP2Client.zig: Core HTTP/2 client implementation (~1,054 lines)
• HTTP2Integration.zig: Integration layer with existing HTTP client infrastructure
• Build System: Proper CMake integration with lshpack dependency
• Test Infrastructure: Comprehensive test suites for various scenarios

❌ Known Issues and Limitations

Critical Issues

1. ALPN Integration Missing: The implementation does not properly integrate with TLS ALPN negotiation

   • HTTP/2 protocol detection is not working automatically
   • Manual protocol selection is required for testing
   • Real-world HTTPS servers won't negotiate HTTP/2 properly

2. Connection Management:

   • No proper connection pooling for HTTP/2 connections
   • Connection reuse logic may not work correctly
   • Multiplexing benefits are limited without proper connection management

3. Error Handling:

   • Error recovery mechanisms are incomplete
   • Stream reset handling may not work in all scenarios
   • Connection-level errors might not propagate correctly

Integration Issues

1. AsyncHTTP Integration: The integration with existing AsyncHTTP is incomplete

   • Fallback mechanisms are not thoroughly tested
   • Some code paths may not handle HTTP/2 responses correctly
   • Response streaming integration needs work

2. Memory Management:

   • Potential memory leaks in error conditions
   • HPACK encoder/decoder cleanup may be incomplete
   • Stream cleanup on connection termination needs verification

3. Threading:

   • HTTP/2 client integration with Bun's HTTP thread pool is untested
   • Concurrency issues may exist in high-load scenarios

🚧 Testing Status

What Has Been Tested

• Basic HTTP/2 frame parsing and generation
• HPACK compression/decompression functionality
• Simple request/response cycles in controlled environments
• Build system integration and compilation

What Has NOT Been Tested

• Real-world HTTPS server compatibility
• High-concurrency scenarios with multiplexing
• Error conditions and recovery
• Memory usage under load
• Performance compared to HTTP/1.1
• Integration with existing Bun applications

⚠️ Production Readiness: NOT READY

This implementation should be considered experimental and is NOT suitable for production use due to:

1. Incomplete ALPN Integration: Won't work with real HTTPS servers
2. Untested Error Handling: May crash or hang under error conditions
3. Memory Safety: Potential leaks and cleanup issues
4. Performance: May be slower than HTTP/1.1 due to incomplete optimizations
5. Compatibility: May break existing fetch functionality in edge cases

📋 Required Work for Production

High Priority

1. Fix ALPN Integration: Implement proper TLS ALPN negotiation in HTTPContext
2. Connection Pooling: Add proper HTTP/2 connection reuse and management
3. Error Handling: Complete error recovery and stream reset mechanisms
4. Memory Audit: Fix all potential memory leaks and cleanup issues
5. Integration Testing: Extensive testing with real servers and applications

Medium Priority

1. Performance Optimization: Optimize frame processing and memory usage
2. Stream Prioritization: Implement HTTP/2 stream priority handling
3. Server Push: Add support for HTTP/2 server push (if desired)
4. Configuration: Add user-configurable HTTP/2 settings

Low Priority

1. HTTP/2 Specific APIs: Consider exposing HTTP/2-specific features to users
2. Monitoring: Add HTTP/2-specific metrics and debugging
3. Documentation: User-facing documentation for HTTP/2 features

🔧 Development Recommendations

1. Disable by Default: HTTP/2 should be disabled by default until ALPN integration is complete
2. Feature Flag: Add a feature flag or environment variable to enable HTTP/2 for testing
3. Incremental Testing: Start with controlled environments before enabling for general use
4. Memory Testing: Run extensive memory leak detection before production
5. Benchmark: Compare performance with HTTP/1.1 to ensure improvements

📊 Estimated Completion Timeline

• Minimal Viable HTTP/2: 2-3 weeks (ALPN + basic error handling)
• Production Ready: 1-2 months (full testing, optimization, edge cases)
• Feature Complete: 3-4 months (server push, priorities, advanced features)

🎯 Current Recommendation

DO NOT ENABLE this HTTP/2 implementation in production or release builds until:

1. ALPN integration is complete and tested
2. Memory safety has been verified
3. Real-world server compatibility has been validated
4. Performance benefits have been demonstrated

The implementation provides a solid foundation but requires significant additional work before being suitable for end users.

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This status was last updated on 2025-01-04 and reflects the current state of the HTTP/2 client implementation in the claude/add-http2-client-support branch.