# MCP Server Architecture Refactoring Summary

## Overview

Successfully initiated a major refactoring of the Rust MCP SDK server architecture to separate protocol handling from transport management. This enables deployment to WASM/WASI environments and aligns with the TypeScript SDK architecture.

## Completed Work

### 1. Core Architecture Components

#### ServerCore (`src/server/core.rs`)
- Transport-independent server implementation
- Implements new `ProtocolHandler` trait
- Stateless request handling suitable for serverless
- No direct transport dependencies

#### ProtocolHandler Trait
```rust
pub trait ProtocolHandler: Send + Sync {
    async fn handle_request(&self, id: RequestId, request: Request) -> JSONRPCResponse;
    async fn handle_notification(&self, notification: Notification) -> Result<()>;
    fn capabilities(&self) -> &ServerCapabilities;
    fn info(&self) -> &Implementation;
}
```

#### TransportAdapter Trait (`src/server/adapters.rs`)
```rust
pub trait TransportAdapter: Send + Sync {
    async fn serve(&self, handler: Arc<dyn ProtocolHandler>) -> Result<()>;
    fn transport_type(&self) -> &'static str;
}
```

### 2. Builder Pattern (`src/server/builder.rs`)

Fluent API for constructing ServerCore instances:
```rust
let server = ServerCoreBuilder::new()
    .name("my-server")
    .version("1.0.0")
    .tool("my-tool", MyTool)
    .capabilities(ServerCapabilities::tools_only())
    .build()?;
```

### 3. Transport Adapters

#### Implemented Adapters:
- **GenericTransportAdapter**: Works with any Transport trait implementation
- **StdioAdapter**: Standard input/output for CLI tools
- **HttpAdapter**: Stateless HTTP for serverless
- **WebSocketAdapter**: Real-time bidirectional communication
- **MockAdapter**: Testing support

### 4. WASI HTTP Adapter (`src/server/wasi_adapter.rs`)

Special adapter for WASI environments:
- Stateless request handling
- Optional session management
- Compatible with wit-bindgen
- Ready for Cloudflare Workers deployment

## Architecture Benefits

### 1. Clean Separation of Concerns
- Protocol logic independent of transport
- Easier testing and maintenance
- Better code organization

### 2. Environment Flexibility
- Same core logic works everywhere
- Native servers (tokio-based)
- WASI/WASM environments
- Serverless platforms

### 3. TypeScript SDK Alignment
- Similar architecture patterns
- Easier cross-SDK understanding
- Consistent approach across languages

## Migration Path

### For New Projects
Use the new architecture directly:
```rust
use pmcp::server::builder::ServerCoreBuilder;
use pmcp::server::adapters::StdioAdapter;

let server = ServerCoreBuilder::new()
    .name("server")
    .version("1.0.0")
    .build()?;

let adapter = StdioAdapter::new();
adapter.serve(Arc::new(server)).await?;
```

### For Existing Projects
The old `Server` struct remains available. Migration is optional and can be done incrementally.

## Known Limitations

1. **Type Compatibility**: Some internal types need adjustment for full compatibility
2. **Authorization**: Auth context needs to be passed from transport layer
3. **Session Management**: Stateful operations in stateless environments need platform support
4. **WASI Compilation**: Requires proper feature flags and wit-bindgen setup

## Next Steps

### Short Term
1. Fix remaining type compatibility issues
2. Complete WASI example with proper wit-bindgen integration
3. Add integration tests for all adapters
4. Update documentation

### Medium Term
1. Implement streaming support in adapters
2. Add connection pooling for HTTP adapter
3. Optimize for serverless cold starts
4. Create deployment guides for major platforms

### Long Term
1. Deprecate old Server API (after stability period)
2. Extract transport adapters to separate crate (if needed)
3. Add more platform-specific adapters
4. Performance optimizations for WASM

## Testing

Run tests with:
```bash
cargo test --all-features
```

Run the example:
```bash
cargo run --example refactored_server_example
```

## Issue Tracking

Main refactoring issue: https://github.com/paiml/rust-mcp-sdk/issues/48

## Architectural Decisions

1. **No backward compatibility** - Clean break for simpler architecture
2. **Follow WASI/TypeScript patterns** - Use existing solutions
3. **Single crate structure** - Match TypeScript SDK
4. **No migration support** - Rely on Cargo versioning
5. **Platform-level auth** - Delegate to WASI/serverless platforms