## š Refactor: Modernize Legacy SSE Implementation
### Summary
Update the existing `src/sse.ts` legacy SSE server implementation to use modern patterns, improve error handling, and align with the new HTTP server architecture.
### Background
The current `src/sse.ts` file uses deprecated patterns and lacks proper session management. With the new HTTP server implementation as a reference, we should modernize the legacy SSE server while maintaining backwards compatibility.
### Current Issues
- [ ] Uses deprecated `SSEServerTransport` patterns
- [ ] Global transport variable prevents concurrent connections
- [ ] Missing proper error handling and logging
- [ ] No CORS support for web clients
- [ ] Lacks session management and cleanup
- [ ] No health monitoring or status endpoints
### Requirements
#### 1. Architecture Improvements
- [ ] Remove global transport variable
- [ ] Implement proper session management with unique IDs
- [ ] Add session tracking and cleanup
- [ ] Support concurrent SSE connections
- [ ] Align with HTTP server patterns
#### 2. Middleware and Features
- [ ] Add JSON parsing middleware
- [ ] Implement CORS headers
- [ ] Add request logging with session tracking
- [ ] Proper error handling with HTTP status codes
- [ ] Graceful shutdown handling
#### 3. Enhanced Endpoints
- [ ] `/sse` - SSE connection with session ID generation
- [ ] `/messages` - Message handling with session validation
- [ ] `/health` - Health check for SSE server
- [ ] Session ID tracking in headers
#### 4. Error Handling
- [ ] Connection error handling
- [ ] Session validation
- [ ] JSON-RPC 2.0 compliant error responses
- [ ] Proper HTTP status codes
- [ ] Logging for debugging
### Implementation Details
#### Session Management
```typescript
// Store transports by session ID
const transports: Record<string, SSEServerTransport> = {};
// Generate unique session IDs
const sessionId = randomUUID();
// Track sessions in headers
res.setHeader('X-Session-Id', sessionId);
```
#### Enhanced Error Handling
```typescript
try {
// Connection logic
} catch (error) {
console.error('SSE connection error:', error);
if (!res.headersSent) {
res.status(500).send('Failed to establish SSE connection');
}
}
```
#### CORS Support
```typescript
app.use((req, res, next) => {
res.header('Access-Control-Allow-Origin', '*');
res.header('Access-Control-Allow-Methods', 'GET, POST, OPTIONS');
res.header('Access-Control-Allow-Headers', 'Content-Type, X-Session-Id');
next();
});
```
### Acceptance Criteria
#### Functionality
- [ ] SSE server starts without errors
- [ ] Supports multiple concurrent SSE connections
- [ ] Session IDs are properly generated and tracked
- [ ] Messages are routed to correct sessions
- [ ] Cleanup occurs when connections close
#### Error Handling
- [ ] Connection errors are logged and handled gracefully
- [ ] Invalid session IDs return proper error responses
- [ ] JSON-RPC 2.0 compliant error format
- [ ] HTTP status codes match error conditions
#### Integration
- [ ] Works with existing MCP service
- [ ] Compatible with MCP Inspector
- [ ] Maintains backwards compatibility with existing SSE clients
- [ ] Can run alongside HTTP server
#### Code Quality
- [ ] Consistent with HTTP server patterns
- [ ] Proper TypeScript types
- [ ] Comprehensive error handling
- [ ] Clear logging and debugging output
### Migration Impact
ā **No breaking changes** - Existing SSE clients will continue to work without modification.
### Testing Requirements
- [ ] Unit tests for session management
- [ ] Integration tests with multiple concurrent connections
- [ ] Error handling validation
- [ ] Backwards compatibility verification
- [ ] Performance testing under load
### Benefits
1. **Reliability**: Better error handling and session management
2. **Scalability**: Support for concurrent connections
3. **Maintainability**: Consistent patterns with HTTP server
4. **Debugging**: Improved logging and error reporting
5. **Web Support**: CORS enabled for browser clients
### Files Modified
- `src/sse.ts` - Main SSE server implementation
- May need updates to imports and types
### Dependencies
- Should reference patterns from HTTP server implementation (#XX)
- Requires testing with existing SSE clients
- May need documentation updates
---
**Priority**: Medium
**Effort**: Small
**Impact**: Medium - Improves reliability and consistency of legacy transport
