feat: support MCP bridge (#140)

mcp/bridge/README.md

@@ -0,0 +1,42 @@
+# MCP-Bridge
+
+Let MCP tools be used by LLM functions.
+
+## Get Started
+
+1. Create a `mpc.json` at `<llm-functions-dir>`.
+
+```json
+{
+  "mcpServers": {
+    "sqlite": {
+      "command": "uvx",
+      "args": [
+        "mcp-server-sqlite",
+        "--db-path",
+        "/tmp/foo.db"
+      ]
+    },
+    "github": {
+      "command": "npx",
+      "args": [
+        "-y",
+        "@modelcontextprotocol/server-github"
+      ],
+      "env": {
+        "GITHUB_PERSONAL_ACCESS_TOKEN": "<YOUR_TOKEN>"
+      }
+    }
+  }
+}
+```
+
+> MCP-Bridge will launch the server and register all the tools listed by the server. The tool identifier will be `server_toolname` to avoid clashes.
+
+2. Run the bridge server, build mcp tool binaries, update functions.json, all with:
+
+```
+argc mcp start
+```
+
+> Run `argc mcp stop` to stop the bridge server, recover functions.json

mcp/bridge/index.js

@@ -0,0 +1,195 @@
+#!/usr/bin/env node
+
+import * as path from "node:path";
+import * as fs from "node:fs";
+import { Client } from "@modelcontextprotocol/sdk/client/index.js";
+import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";
+import express from "express";
+
+const app = express();
+const PORT = process.env.MCP_BRIDGE_PORT || 8808;
+
+let [rootDir] = process.argv.slice(2);
+
+if (!rootDir) {
+  console.error("Usage: mcp-bridge <llm-functions-dir>");
+  process.exit(1);
+}
+
+let mcpServers = {};
+const mcpJsonPath = path.join(rootDir, "mcp.json");
+try {
+  const data = await fs.promises.readFile(mcpJsonPath, "utf8");
+  mcpServers = JSON.parse(data)?.mcpServers;
+} catch {
+  console.error(`Failed to read json at '${mcpJsonPath}'`);
+  process.exit(1);
+}
+
+async function startMcpServer(id, serverConfig) {
+  console.log(`Starting ${id} server...`);
+  const capabilities = { tools: {} };
+  const transport = new StdioClientTransport({
+    ...serverConfig,
+  });
+  const client = new Client(
+    { name: id, version: "1.0.0" },
+    { capabilities }
+  );
+  await client.connect(transport);
+  const { tools: toolDefinitions } = await client.listTools()
+  const tools = toolDefinitions.map(
+    ({ name, description, inputSchema }) =>
+    ({
+      spec: {
+        name: `${normalizeToolName(`${id}_${name}`)}`,
+        description,
+        parameters: inputSchema,
+      },
+      impl: async args => {
+        const res = await client.callTool({
+          name: name,
+          arguments: args,
+        });
+        const content = res.content;
+        let text = arrayify(content)?.map(c => {
+          switch (c.type) {
+            case "text":
+              return c.text || ""
+            case "image":
+              return c.data
+            case "resource":
+              return c.resource?.uri || ""
+            default:
+              return c
+          }
+        }).join("\n");
+        if (res.isError) {
+          text = `Tool Error\n${text}`;
+        }
+        return text;
+      },
+    })
+  );
+  return {
+    tools,
+    [Symbol.asyncDispose]: async () => {
+      try {
+        console.log(`Closing ${id} server...`);
+        await client.close();
+        await transport.close();
+      } catch { }
+    },
+  }
+}
+
+async function runBridge() {
+  let hasError = false;
+  let runningMcpServers = await Promise.all(
+    Object.entries(mcpServers).map(
+      async ([name, serverConfig]) => {
+        try {
+          return await startMcpServer(name, serverConfig)
+        } catch (err) {
+          hasError = true;
+          console.error(`Failed to start ${name} server; ${err.message}`)
+        }
+      }
+    )
+  );
+  runningMcpServers = runningMcpServers.filter(s => !!s);
+  const stopMcpServers = () => Promise.all(runningMcpServers.map(s => s[Symbol.asyncDispose]()));
+  if (hasError) {
+    await stopMcpServers();
+    return;
+  }
+
+  const definitions = runningMcpServers.flatMap(s => s.tools.map(t => t.spec));
+  const runTool = async (name, args) => {
+    for (const server of runningMcpServers) {
+      const tool = server.tools.find(t => t.spec.name === name);
+      if (tool) {
+        return tool.impl(args);
+      }
+    }
+    return `Not found tool '${name}'`;
+  };
+
+  app.use((err, _req, res, _next) => {
+    res.status(500).send(err?.message || err);
+  });
+
+  app.use(express.json());
+
+  app.get("/", (_req, res) => {
+    res.send(`# MCP Bridge API
+  
+- POST /tools/:name 
+  \`\`\`
+  curl -X POST http://localhost:8808/tools/filesystem_write_file  \\
+    -H 'content-type: application/json' \\
+    -d '{"path": "/tmp/file1", "content": "hello world"}'
+  \`\`\`
+- GET /tools
+  \`\`\`
+  curl http://localhost:8808/tools
+  \`\`\`
+  `);
+  });
+
+  app.get("/tools", (_req, res) => {
+    res.json(definitions);
+  });
+
+  app.post("/tools/:name", async (req, res) => {
+    try {
+      const output = await runTool(req.params.name, req.body);
+      res.send(output);
+    } catch (err) {
+      res.status(500).send(err);
+    }
+  });
+
+  app.get("/pid", (_req, res) => {
+    res.send(process.pid.toString());
+  });
+
+  app.get("/health", (_req, res) => {
+    res.send("OK");
+  });
+
+  app.use((_req, res, _next) => {
+    res.status(404).send("Not found");
+  });
+
+  const server = app.listen(PORT, () => {
+    console.log(`Server is running on port ${PORT}`);
+  });
+
+  return async () => {
+    server.close(() => console.log("Http server closed"));
+    await stopMcpServers();
+  };
+}
+
+function arrayify(a) {
+  let r;
+  if (a === undefined) r = [];
+  else if (Array.isArray(a)) r = a.slice(0);
+  else r = [a];
+
+  return r
+}
+
+function normalizeToolName(name) {
+  return name.toLowerCase().replace(/-/g, "_");
+}
+
+runBridge()
+  .then(stop => {
+    if (stop) {
+      process.on('SIGINT', stop);
+      process.on('SIGTERM', stop);
+    }
+  })
+  .catch(console.error);

mcp/bridge/package.json

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+{
+  "name": "mcp-bridge",
+  "version": "1.0.0",
+  "description": "Let MCP tools be used by LLM functions",
+  "license": "MIT",
+  "author": "sigoden <sigoden@gmail.com>",
+  "homepage": "https://github.com/sigoden/llm-functions/tree/main/mcp/bridge",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/sigoden/llm-functions.git",
+    "directory": "mcp/bridge"
+  },
+  "private": true,
+  "type": "module",
+  "bin": {
+    "mcp-bridge": "index.js"
+  },
+  "dependencies": {
+    "@modelcontextprotocol/sdk": "^1.0.3",
+    "express": "^4.21.2"
+  }
+}