Senior LevelAI, LLMs, Embeddings & MCP
How do you build custom Transport Layers for Model Context Protocol (MCP) using gRPC or WebSockets?
❓ Interview Prompt: Explain implementing the MCP SDK Transport interface, message serialization, and connection lifecycle handlers.
While Stdio and SSE are the default transports, production enterprise clusters often require custom low-latency WebSocket or gRPC Transport Layers for MCP.
Implementation Requirements:
A custom transport must implement the MCP SDK Transport interface:
1
`start()`: Opens network socket / stream.
2
`send(message: JSONRPCMessage)`: Serializes and transmits JSON-RPC protocol frames.
3
`close()`: Performs clean socket teardown.
4
`onmessage` / `onclose` / `onerror` callbacks: Emits incoming messages back to the server/client protocol layer.
Code Implementation Example
typescript
import { Transport } from '@modelcontextprotocol/sdk/shared/transport.js';
import { JSONRPCMessage } from '@modelcontextprotocol/sdk/types.js';
import WebSocket from 'ws';
export class WebSocketClientTransport implements Transport {
private ws: WebSocket | null = null;
onmessage?: (message: JSONRPCMessage) => void;
onclose?: () => void;
onerror?: (error: Error) => void;
constructor(private url: string) {}
async start(): Promise<void> {
this.ws = new WebSocket(this.url);
this.ws.on('message', (data) => {
const msg = JSON.parse(data.toString());
this.onmessage?.(msg);
});
this.ws.on('close', () => this.onclose?.());
}
async send(message: JSONRPCMessage): Promise<void> {
this.ws?.send(JSON.stringify(message));
}
async close(): Promise<void> { this.ws?.close(); }
}💡Custom WebSocket Transport class implementing MCP SDK Transport interface.
🎯 Interview Key Takeaway
Custom MCP transports implement the SDK Transport interface, mapping JSON-RPC protocol frames over WebSockets or gRPC streams.
#MCP#Transport#WebSockets#gRPC#Senior
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