Second Opinion MCP Server
An MCP server that provides AI-powered assistance for coding problems by combining insights from:
- Google's Gemini AI
- Stack Overflow accepted answers
- Perplexity AI analysis
Features
- Get detailed solutions for coding problems with context from multiple sources
- Automatic language detection from file extensions
- Code snippet extraction and formatting
- Markdown report generation for solutions
- Git-aware file context gathering
Setup
- Install dependencies:
npm install
- Build the server:
npm run build
- Configure environment variables in MCP settings:
{
"mcpServers": {
"second-opinion": {
"command": "node",
"args": ["/path/to/second-opinion-server/build/index.js"],
"env": {
"GEMINI_API_KEY": "your-gemini-api-key",
"PERPLEXITY_API_KEY": "your-perplexity-api-key",
"STACK_EXCHANGE_KEY": "your-stack-exchange-key"
}
}
}
}
Required environment variables:
GEMINI_API_KEY: Google's Gemini AI API keyPERPLEXITY_API_KEY: Perplexity AI API keySTACK_EXCHANGE_KEY: Stack Exchange API key (optional, uses anonymous access if not provided)
Usage
The server provides a single tool:
get_second_opinion
Get AI-powered insights and solutions for coding problems.
Input Schema:
{
"goal": "string (required) - What you're trying to accomplish",
"error": "string (optional) - Any error messages you're seeing",
"code": "string (optional) - Relevant code context",
"solutionsTried": "string (optional) - What solutions you've already tried",
"filePath": "string (optional) - Path to the file with the issue"
}
Example Input:
{
"goal": "Fix React useEffect cleanup error",
"error": "React Hook useEffect has a missing dependency: 'socket'. Either include it in the dependency array, or remove the dependency array react-hooks/exhaustive-deps",
"code": "useEffect(() => {\n socket.on('message', handleMessage);\n return () => socket.off('message');\n}, []);",
"solutionsTried": "I tried adding socket to the dependency array but then it causes infinite re-renders"
}
Example Response:
Understanding the Problem
The core issue lies in how React's useEffect hook manages side effects and their dependencies. When you provide an empty dependency array ([]), you're telling React that the effect should only run once when the component mounts and that the cleanup function should run when the component unmounts.
However, in your code, the socket object is used within the effect. This creates a closure where the handleMessage function and the cleanup function (socket.off('message')) implicitly depend on the current value of socket. If socket ever changes (e.g., due to a reconnection or reinitialization), your effect will be using an outdated socket instance.
Common Issues
- Stale Closures: The event handler (
handleMessage) might be working with an old socket object
- Incorrect Cleanup: The
socket.off('message') might not remove the intended event listener
- Memory Leaks: Failed cleanup can lead to memory leaks and unexpected behavior
Solutions
1. Using useRef for Stable References
import React, { useEffect, useRef } from 'react';
function MyComponent({ socket }) {
const socketRef = useRef(socket);
useEffect(() => {
const currentSocket = socketRef.current;
currentSocket.on('message', handleMessage);
return () => {
currentSocket.off('message');
};
}, []); // Empty dependency array is now safe
}
Why This Works:
useRef creates a mutable object that persists across renders- The ref object itself doesn't change, preventing effect re-runs
- You can access the latest socket value via the ref
2. Using useCallback for Handlers
import React, { useEffect, useRef, useCallback } from 'react';
function MyComponent({ socket, someProp }) {
const socketRef = useRef(socket);
const handleMessage = useCallback((message) => {
// Do something with the message and potentially someProp
console.log(message, someProp);
}, [someProp]); // Include dependencies of handleMessage
useEffect(() => {
const currentSocket = socketRef.current;
currentSocket.on('message', handleMessage);
return () => {
currentSocket.off('message', handleMessage);
};
}, [handleMessage]); // Depend on the memoized handler
}
3. Managing Socket Lifecycle Inside useEffect
import React, { useEffect, useState } from 'react';
function MyComponent() {
const [messages, setMessages] = useState([]);
useEffect(() => {
const socket = new WebSocket('your_websocket_url');
const handleMessage = (message) => {
setMessages((prevMessages) => [...prevMessages, message]);
};
socket.on('message', handleMessage);
return () => {
socket.off('message', handleMessage);
socket.close();
};
}, []); // Empty array is correct - socket lifecycle managed within
}
4. Custom Hook Solution
function useSocket(url) {
const [messages, setMessages] = useState([]);
const socketRef = useRef(null);
useEffect(() => {
const socket = new WebSocket(url);
socketRef.current = socket;
const handleMessage = (message) => {
setMessages((prevMessages) => [...prevMessages, message]);
};
socket.on('message', handleMessage);
return () => {
socket.off('message', handleMessage);
socket.close();
};
}, [url]);
const sendMessage = useCallback((message) => {
if (socketRef.current?.readyState === WebSocket.OPEN) {
socketRef.current.send(message);
}
}, []);
return { messages, sendMessage };
}
Best Practices
- Dependency Management
* Use `useRef` for stable references
* Memoize handlers with `useCallback`
* Consider socket lifecycle management
- Performance Optimization
* Minimize unnecessary re-renders
* Handle high-volume messages efficiently
* Use appropriate cleanup patterns
- Error Handling
* Handle connection errors gracefully
* Implement reconnection logic if needed
* Clean up resources properly
- Testing Considerations
* Mock WebSocket connections in tests
* Verify event listener cleanup
* Test error scenarios
Project Structure
src/
├── config.ts # Configuration and API settings
├── fileUtils.ts # File operations and language detection
├── index.ts # Entry point
├── perplexity.ts # Perplexity AI integration
├── server.ts # MCP server implementation
├── stackOverflow.ts # Stack Overflow API integration
└── types.ts # TypeScript interfaces
Known Issues
See errors.md for current issues and workarounds.
