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Architecture Overview

System Architecture

┌─────────────┐    MCP Protocol    ┌──────────────────┐   MCP Protocol   ┌────────────┐    XPC    ┌─────────┐
│   Cursor    │ ◄────────────────► │  xcodemcpwrapper │ ◄──────────────► │ mcpbridge  │ ◄───────► │  Xcode  │
│ (MCP Client)│                    │  (This Project)  │                  │  (Bridge)  │           │  (IDE)  │
└─────────────┘                    └──────────────────┘                  └────────────┘           └─────────┘

Data Flow

  1. stdin → Wrapper receives MCP requests from client
  2. Wrapper forwards requests unchanged to mcpbridge
  3. mcpbridge → Communicates with Xcode via XPC
  4. stdout → mcpbridge returns responses
  5. Wrapper detects non-compliant responses (missing structuredContent)
  6. Wrapper extracts text from content array, parses as JSON
  7. Wrapper injects structuredContent field into response
  8. stdout → Client receives compliant MCP response

Key Components

bridge.py

  • create_bridge() - Spawns mcpbridge subprocess
  • forward_stdin() - Forwards stdin to bridge
  • read_stdout() - Reads stdout line-by-line
  • cleanup_bridge() - Handles process termination

transform.py

  • process_response_line() - Main transformation entry point
  • needs_transformation() - Detects non-compliant responses
  • extract_text_content() - Extracts text from content array
  • inject_structured_content() - Adds structuredContent field

__main__.py

  • Sets up stdin/stdout threads
  • Runs the main event loop
  • Handles cleanup on exit

Response Transformation

# Input from mcpbridge (non-compliant)
{
  "result": {
    "content": [{"type": "text", "text": '{"status": "ok"}'}]
  }
}

# Output from wrapper (MCP compliant)
{
  "result": {
    "content": [{"type": "text", "text": '{"status": "ok"}'}],
    "structuredContent": {"status": "ok"}
  }
}

Performance

  • Line-buffered I/O for minimal latency
  • Average overhead: <0.01ms per transformation
  • Memory usage: <10MB

Data Storage

For a full reference on the SQLite metrics database, in-memory collector, and audit log files, see Data Storage Reference.