# CLAUDE.md - Project Context

This file provides context for Claude when working on this project.

## Project Overview

**LabMCP** is a collection of Model Context Protocol (MCP) servers written in Go, designed to extend Claude's capabilities with custom tools. The repository is structured to be generic and extensible, allowing multiple MCP servers to be added over time.

## Current Focus: NixOS Options MCP Server

The first MCP server provides search and query capabilities for NixOS configuration options. This addresses the challenge of incomplete or hard-to-find documentation in the Nix ecosystem.

## Technology Stack

- **Language**: Go 1.24+
- **Build System**: Nix flakes
- **Databases**: PostgreSQL and SQLite (both fully supported)
- **Protocol**: MCP (Model Context Protocol) - JSON-RPC over STDIO or HTTP/SSE
- **Module Path**: `git.t-juice.club/torjus/labmcp`

## Project Status

**Complete and maintained** - All core features implemented:
- Full MCP server with 6 tools
- PostgreSQL and SQLite backends with FTS
- NixOS module for deployment
- CLI for manual operations
- Comprehensive test suite

## Repository Structure

```
labmcp/
├── cmd/
│   └── nixos-options/
│       └── main.go             # CLI entry point
├── internal/
│   ├── database/
│   │   ├── interface.go        # Store interface
│   │   ├── schema.go           # Schema versioning
│   │   ├── postgres.go         # PostgreSQL implementation
│   │   ├── sqlite.go           # SQLite implementation
│   │   └── *_test.go           # Database tests
│   ├── mcp/
│   │   ├── server.go           # MCP server core
│   │   ├── handlers.go         # Tool implementations
│   │   ├── types.go            # Protocol types
│   │   ├── transport.go        # Transport interface
│   │   ├── transport_stdio.go  # STDIO transport
│   │   ├── transport_http.go   # HTTP/SSE transport
│   │   ├── session.go          # HTTP session management
│   │   └── *_test.go           # MCP tests
│   └── nixos/
│       ├── indexer.go          # Nixpkgs indexing
│       ├── parser.go           # options.json parsing
│       ├── types.go            # Channel aliases, extensions
│       └── *_test.go           # Indexer tests
├── nix/
│   ├── module.nix              # NixOS module
│   └── package.nix             # Nix package definition
├── testdata/
│   └── options-sample.json     # Test fixture
├── flake.nix
├── go.mod
├── .mcp.json                   # MCP client configuration
├── CLAUDE.md                   # This file
├── README.md
└── TODO.md                     # Future improvements
```

## MCP Tools

All tools are implemented and functional:

| Tool | Description |
|------|-------------|
| `search_options` | Full-text search across option names and descriptions |
| `get_option` | Get full details for a specific option with children |
| `get_file` | Fetch source file contents from indexed nixpkgs |
| `index_revision` | Index a nixpkgs revision (by hash or channel name) |
| `list_revisions` | List all indexed revisions |
| `delete_revision` | Delete an indexed revision |

## Key Implementation Details

### Database
- Schema versioning with automatic recreation on version mismatch
- Full-text search: SQLite FTS5, PostgreSQL tsvector/GIN
- Path-based queries use LIKE for exact prefix matching
- Batch operations for efficient indexing

### Indexing
- Uses `nix-build` to evaluate NixOS options from any nixpkgs revision
- File indexing downloads tarball and stores allowed extensions (.nix, .json, .md, etc.)
- File indexing enabled by default (use `--no-files` to skip)
- Skips already-indexed revisions (use `--force` to re-index)

### Transports
- **STDIO**: Default transport, line-delimited JSON-RPC (for CLI/desktop MCP clients)
- **HTTP**: Streamable HTTP transport with SSE (for web-based MCP clients)
  - Session management with cryptographically secure IDs
  - Configurable CORS (localhost-only by default)
  - Optional TLS support
  - SSE keepalive messages (15s default)

### Security
- Revision parameter validated against strict regex to prevent Nix injection
- Path traversal protection using `filepath.Clean()` and `filepath.IsAbs()`
- NixOS module supports `connectionStringFile` for PostgreSQL secrets
- Systemd service runs with extensive hardening options
- HTTP transport hardening:
  - Request body size limit (1MB default)
  - Server timeouts (read: 30s, write: 30s, idle: 120s, header: 10s)
  - Maximum session limit (10,000 default)
  - Origin validation for CORS

## CLI Commands

```bash
nixos-options serve                    # Run MCP server on STDIO (default)
nixos-options serve --transport http   # Run MCP server on HTTP
nixos-options serve --transport http \
  --http-address 0.0.0.0:8080 \
  --allowed-origins https://example.com  # HTTP with custom config
nixos-options index <revision>         # Index a nixpkgs revision
nixos-options index --force <r>        # Force re-index existing revision
nixos-options index --no-files         # Skip file content indexing
nixos-options list                     # List indexed revisions
nixos-options search <query>           # Search options
nixos-options get <option>             # Get option details
nixos-options delete <revision>        # Delete indexed revision
nixos-options --version                # Show version
```

## Notes for Claude

### Development Workflow
- **Always run `go fmt ./...` before committing Go code**
- **Run Go commands using `nix develop -c`** (e.g., `nix develop -c go test ./...`)
- **Use `nix run` to run binaries** (e.g., `nix run .#nixos-options -- serve`)
- File paths in responses should use format `path/to/file.go:123`

### User Preferences
- User prefers PostgreSQL over SQLite (has homelab infrastructure)
- User values good test coverage and benchmarking
- Project should remain generic to support future MCP servers

### Testing
```bash
# Run all tests
nix develop -c go test ./... -short

# Run with verbose output
nix develop -c go test ./... -v

# Run benchmarks (requires nix-build)
nix develop -c go test -bench=. -benchtime=1x -timeout=30m ./internal/nixos/...
```

### Building
```bash
# Build with nix
nix build

# Run directly
nix run . -- serve
nix run . -- index nixos-unstable
```