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| 1 | +import type { VercelRequest, VercelResponse } from '@vercel/node'; |
| 2 | +import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js'; |
| 3 | +import { McpServerlessService } from '../src/mcp/mcp-serverless'; |
| 4 | + |
| 5 | +// Constants |
| 6 | +const MAX_BODY_SIZE = 1024 * 1024; // 1MB limit |
| 7 | +const ALLOWED_METHODS = ['GET', 'POST', 'DELETE', 'OPTIONS']; |
| 8 | + |
| 9 | +// Singleton service instance (reused across warm invocations) |
| 10 | +let mcpService: McpServerlessService | null = null; |
| 11 | + |
| 12 | +function getService(): McpServerlessService { |
| 13 | + if (!mcpService) { |
| 14 | + mcpService = new McpServerlessService(); |
| 15 | + } |
| 16 | + return mcpService; |
| 17 | +} |
| 18 | + |
| 19 | +function jsonRpcError( |
| 20 | + res: VercelResponse, |
| 21 | + code: number, |
| 22 | + message: string, |
| 23 | + status: number = 500, |
| 24 | +): void { |
| 25 | + res.status(status).json({ |
| 26 | + jsonrpc: '2.0', |
| 27 | + error: { code, message }, |
| 28 | + id: null, |
| 29 | + }); |
| 30 | +} |
| 31 | + |
| 32 | +async function parseBody(req: VercelRequest): Promise<unknown> { |
| 33 | + // Vercel may already parse body in some cases |
| 34 | + if (req.body && typeof req.body === 'object') { |
| 35 | + return req.body; |
| 36 | + } |
| 37 | + |
| 38 | + // Manual parsing for streaming body |
| 39 | + const chunks: Buffer[] = []; |
| 40 | + let totalSize = 0; |
| 41 | + |
| 42 | + for await (const chunk of req as unknown as AsyncIterable<Buffer>) { |
| 43 | + totalSize += chunk.length; |
| 44 | + if (totalSize > MAX_BODY_SIZE) { |
| 45 | + throw new Error('PAYLOAD_TOO_LARGE'); |
| 46 | + } |
| 47 | + chunks.push(chunk); |
| 48 | + } |
| 49 | + |
| 50 | + if (chunks.length === 0) { |
| 51 | + return undefined; |
| 52 | + } |
| 53 | + |
| 54 | + const bodyStr = Buffer.concat(chunks).toString('utf-8'); |
| 55 | + return JSON.parse(bodyStr); |
| 56 | +} |
| 57 | + |
| 58 | +export default async function handler( |
| 59 | + req: VercelRequest, |
| 60 | + res: VercelResponse, |
| 61 | +): Promise<void> { |
| 62 | + // CORS headers |
| 63 | + res.setHeader('Access-Control-Allow-Origin', '*'); |
| 64 | + res.setHeader('Access-Control-Allow-Methods', ALLOWED_METHODS.join(', ')); |
| 65 | + res.setHeader('Access-Control-Allow-Headers', 'Content-Type, mcp-session-id'); |
| 66 | + |
| 67 | + // Handle preflight |
| 68 | + if (req.method === 'OPTIONS') { |
| 69 | + res.status(200).end(); |
| 70 | + return; |
| 71 | + } |
| 72 | + |
| 73 | + // Validate method |
| 74 | + if (!req.method || !ALLOWED_METHODS.includes(req.method)) { |
| 75 | + return jsonRpcError(res, -32600, 'Method not allowed', 405); |
| 76 | + } |
| 77 | + |
| 78 | + // Check Content-Length header for early rejection |
| 79 | + const contentLength = req.headers['content-length']; |
| 80 | + if (contentLength && parseInt(contentLength, 10) > MAX_BODY_SIZE) { |
| 81 | + return jsonRpcError(res, -32700, 'Request entity too large', 413); |
| 82 | + } |
| 83 | + |
| 84 | + // Validate Content-Type for POST |
| 85 | + if (req.method === 'POST') { |
| 86 | + const contentType = req.headers['content-type'] || ''; |
| 87 | + if (!contentType.includes('application/json')) { |
| 88 | + return jsonRpcError( |
| 89 | + res, |
| 90 | + -32700, |
| 91 | + 'Unsupported Media Type: expected application/json', |
| 92 | + 415, |
| 93 | + ); |
| 94 | + } |
| 95 | + } |
| 96 | + |
| 97 | + try { |
| 98 | + // Parse request body |
| 99 | + let body: unknown; |
| 100 | + if (req.method === 'POST') { |
| 101 | + try { |
| 102 | + body = await parseBody(req); |
| 103 | + } catch (parseError) { |
| 104 | + if ( |
| 105 | + parseError instanceof Error && |
| 106 | + parseError.message === 'PAYLOAD_TOO_LARGE' |
| 107 | + ) { |
| 108 | + return jsonRpcError(res, -32700, 'Request entity too large', 413); |
| 109 | + } |
| 110 | + console.error('Body parse error:', parseError); |
| 111 | + return jsonRpcError(res, -32700, 'Parse error: invalid JSON', 400); |
| 112 | + } |
| 113 | + } |
| 114 | + |
| 115 | + const service = getService(); |
| 116 | + const server = service.getServer(); |
| 117 | + |
| 118 | + // Create stateless transport for this request |
| 119 | + const transport = new StreamableHTTPServerTransport({ |
| 120 | + sessionIdGenerator: undefined, // Stateless mode |
| 121 | + enableJsonResponse: true, |
| 122 | + }); |
| 123 | + |
| 124 | + // Connect server to transport |
| 125 | + await server.connect(transport); |
| 126 | + |
| 127 | + // Handle the request |
| 128 | + await transport.handleRequest( |
| 129 | + req as unknown as import('express').Request, |
| 130 | + res as unknown as import('express').Response, |
| 131 | + body, |
| 132 | + ); |
| 133 | + } catch (error) { |
| 134 | + console.error('MCP handler error:', error); |
| 135 | + const message = |
| 136 | + error instanceof Error ? error.message : 'Internal server error'; |
| 137 | + return jsonRpcError(res, -32603, message); |
| 138 | + } |
| 139 | +} |
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