joakimp
7eec49b9b8
Mirrors /ext UX (space=stage, enter=apply+reload, esc=cancel) but for MCP servers in the settings.json `mcp` block. Tracks per-server runtime state captured at extension load time so users can see at a glance which servers are running / failed / disabled / remote-skipped / invalid, with tool counts for the running ones. Toggling writes back to settings.json — disabling sets enabled:false, re-enabling removes the explicit key (default is true) to keep the file tidy. Then ctx.reload() picks up the change. Closes the visibility gap surfaced by 'searxng_search isn't in /ext': MCP-provided tools are runtime-spawned, not file-based extensions, so they need their own list view. /mcp fills that hole.
597 lines
20 KiB
TypeScript
597 lines
20 KiB
TypeScript
/**
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* MCP Loader Extension
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*
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* Reads an `mcp` block from pi's settings.json (same shape as opencode and
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* Claude Desktop) and connects to each declared server, exposing all of
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* their tools to pi as native tools.
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*
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* Settings.json shape:
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*
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* {
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* "mcp": {
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* "searxng": {
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* "type": "local",
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* "command": ["uvx", "mcp-searxng"],
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* "env": { "SEARXNG_URL": "https://searxng.your-host.lan" }
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* },
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* "gitea": {
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* "type": "local",
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* "command": ["gitea-mcp", "-t", "stdio"],
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* "enabled": false,
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* "env": { "GITEA_ACCESS_TOKEN": "...", "GITEA_HOST": "..." }
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* },
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* "context7": {
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* "type": "remote",
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* "url": "https://mcp.context7.com/mcp"
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* }
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* }
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* }
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*
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* Per-server keys:
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* type "local" (stdio subprocess) | "remote" (streamable-http)
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* command argv array — first element is the executable, rest are args.
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* For local servers only.
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* url remote MCP endpoint URL. For remote servers only.
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* enabled default true. Set false to disable a server without
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* removing it from settings.json.
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* env optional object of environment variables to inject into
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* the spawned subprocess. Inherits parent env first, then
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* overlays these keys.
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*
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* Tool naming
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*
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* Each MCP tool is registered with pi as `<server-name>_<tool-name>` to
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* avoid collisions across servers. If the tool name already begins with
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* `<server-name>_` (e.g. mempalace's tools are `mempalace_search` etc.)
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* the prefix is not duplicated.
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*
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* Lifecycle
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*
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* • Servers are spawned at extension load time (pi startup or /reload).
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* • Each server's `tools/list` is awaited before pi finishes registering.
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* • Subprocess stderr is silenced unless PI_MCP_LOADER_DEBUG=1.
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* • Subprocesses receive SIGTERM at session_shutdown.
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* • A server that fails to start (binary missing, init handshake error)
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* logs a single line to stderr and is skipped. Other servers continue.
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* Pi keeps working without that server's tools.
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*
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* Limitations (v1)
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*
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* • Only local/stdio transport is implemented. Remote (streamable-http,
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* SSE) servers are detected and skipped with a warning. v2 will add
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* remote support — context7 is the prime motivator.
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* • No reconnect: if a subprocess dies mid-session, its tools become
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* unavailable until pi is reloaded. The mempalace.ts extension has
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* the same limitation today.
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*
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* Coexistence with mempalace.ts
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*
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* The mempalace.ts extension already spawns mempalace-mcp directly with
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* bespoke handling (agent identity injection from $MEMPALACE_AGENT_NAME,
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* wake-up context). This loader does NOT touch mempalace — leave the
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* bespoke extension in place. If you also list mempalace under the `mcp`
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* block in settings.json the loader will register a parallel set of
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* tools, which is harmless but redundant. Don't.
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*
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* Slash command
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*
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* `/mcp` lists configured MCP servers with their runtime status
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* (running / failed / disabled / remote-skipped / invalid) and lets
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* you toggle the `enabled` flag in settings.json. Same UX as `/ext`:
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* space stages, enter applies + reloads, esc cancels.
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*/
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import { type ChildProcessWithoutNullStreams, spawn } from "node:child_process";
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import * as fs from "node:fs";
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import * as os from "node:os";
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import * as path from "node:path";
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import {
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type ExtensionAPI,
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getSettingsListTheme,
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} from "@mariozechner/pi-coding-agent";
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import {
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Container,
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Key,
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matchesKey,
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type SettingItem,
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SettingsList,
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} from "@mariozechner/pi-tui";
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import { Type } from "typebox";
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// ── MCP types ────────────────────────────────────────────────────────────────
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type McpTool = {
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name: string;
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description?: string;
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inputSchema?: Record<string, unknown>;
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};
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type LocalServerConfig = {
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type?: "local";
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command: string[];
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env?: Record<string, string>;
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enabled?: boolean;
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};
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type RemoteServerConfig = {
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type: "remote";
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url: string;
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enabled?: boolean;
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};
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type ServerConfig = LocalServerConfig | RemoteServerConfig;
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const SETTINGS_PATH = path.join(os.homedir(), ".pi", "agent", "settings.json");
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const DEBUG = process.env.PI_MCP_LOADER_DEBUG === "1";
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function dlog(msg: string) {
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if (DEBUG) process.stderr.write(`[mcp-loader] ${msg}\n`);
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}
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function warn(msg: string) {
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process.stderr.write(`[mcp-loader] ${msg}\n`);
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}
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// ── Settings.json reader ─────────────────────────────────────────────────────
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function readMcpServers(): Record<string, ServerConfig> {
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if (!fs.existsSync(SETTINGS_PATH)) {
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dlog(`no settings.json at ${SETTINGS_PATH}`);
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return {};
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}
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let raw: string;
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try {
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raw = fs.readFileSync(SETTINGS_PATH, "utf8");
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} catch (err) {
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warn(`could not read ${SETTINGS_PATH}: ${(err as Error).message}`);
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return {};
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}
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let parsed: any;
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try {
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parsed = JSON.parse(raw);
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} catch (err) {
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warn(`settings.json parse error: ${(err as Error).message}`);
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return {};
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}
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const block = parsed?.mcp;
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if (!block || typeof block !== "object") {
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dlog("no `mcp` block in settings.json");
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return {};
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}
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return block as Record<string, ServerConfig>;
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}
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// ── Stdio MCP client ─────────────────────────────────────────────────────────
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class StdioMcpClient {
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private proc: ChildProcessWithoutNullStreams | null = null;
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private nextId = 1;
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private pending = new Map<number, { resolve: (v: any) => void; reject: (e: Error) => void }>();
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private stdoutBuf = "";
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private serverName: string;
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public tools: McpTool[] = [];
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constructor(serverName: string) {
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this.serverName = serverName;
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}
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async start(command: string, args: string[], env?: Record<string, string>): Promise<void> {
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const childEnv = { ...process.env, ...(env ?? {}) };
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this.proc = spawn(command, args, { stdio: ["pipe", "pipe", "pipe"], env: childEnv });
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this.proc.on("error", (err) => this.failAll(err));
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this.proc.on("exit", (code, signal) => {
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this.failAll(new Error(`${this.serverName}: subprocess exited (code=${code}, signal=${signal})`));
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});
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this.proc.stdout.setEncoding("utf8");
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this.proc.stdout.on("data", (chunk: string) => this.onStdout(chunk));
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this.proc.stderr.setEncoding("utf8");
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if (DEBUG) {
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this.proc.stderr.on("data", (chunk: string) => {
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process.stderr.write(`[${this.serverName} stderr] ${chunk}`);
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});
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} else {
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this.proc.stderr.resume(); // drain without logging
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}
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// MCP initialize handshake
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await this.request("initialize", {
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protocolVersion: "2024-11-05",
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capabilities: {},
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clientInfo: { name: "pi-mcp-loader", version: "0.1.0" },
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});
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this.notify("notifications/initialized", {});
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const listed = await this.request("tools/list", {});
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this.tools = (listed?.tools as McpTool[]) ?? [];
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}
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private onStdout(chunk: string) {
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this.stdoutBuf += chunk;
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let nl: number;
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while ((nl = this.stdoutBuf.indexOf("\n")) !== -1) {
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const line = this.stdoutBuf.slice(0, nl).trim();
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this.stdoutBuf = this.stdoutBuf.slice(nl + 1);
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if (!line) continue;
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let msg: any;
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try {
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msg = JSON.parse(line);
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} catch {
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continue;
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}
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if (typeof msg.id === "number" && this.pending.has(msg.id)) {
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const { resolve, reject } = this.pending.get(msg.id)!;
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this.pending.delete(msg.id);
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if (msg.error) reject(new Error(msg.error.message ?? "MCP error"));
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else resolve(msg.result);
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}
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// notifications (no id) ignored.
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}
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}
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private failAll(err: Error) {
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for (const { reject } of this.pending.values()) reject(err);
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this.pending.clear();
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}
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private write(obj: unknown) {
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if (!this.proc) throw new Error(`${this.serverName}: not started`);
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this.proc.stdin.write(`${JSON.stringify(obj)}\n`);
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}
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private notify(method: string, params: unknown) {
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this.write({ jsonrpc: "2.0", method, params });
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}
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request(method: string, params: unknown): Promise<any> {
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const id = this.nextId++;
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return new Promise((resolve, reject) => {
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this.pending.set(id, { resolve, reject });
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this.write({ jsonrpc: "2.0", id, method, params });
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});
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}
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async callTool(name: string, args: Record<string, unknown>): Promise<any> {
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return this.request("tools/call", { name, arguments: args });
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}
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stop() {
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if (this.proc) {
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try {
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this.proc.kill("SIGTERM");
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} catch {}
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this.proc = null;
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}
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}
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}
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// ── MCP result → pi tool result helpers ──────────────────────────────────────
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function extractText(mcpResult: any): string {
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if (!mcpResult) return "";
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const content = mcpResult.content;
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if (!Array.isArray(content)) return JSON.stringify(mcpResult);
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return content
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.map((c: any) => {
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if (c?.type === "text" && typeof c.text === "string") return c.text;
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return JSON.stringify(c);
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})
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.join("\n");
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}
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function namespacedToolName(serverName: string, toolName: string): string {
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// Avoid double-prefix: if the MCP server already names its tools
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// `<serverName>_<...>`, leave them alone.
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const prefix = `${serverName}_`;
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if (toolName.startsWith(prefix)) return toolName;
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return `${prefix}${toolName}`;
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}
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// ── Settings.json writer ─────────────────────────────────────────────────────
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/**
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* Flip the `enabled` flag for a server in settings.json and write back.
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* Preserves all other keys verbatim by round-tripping through JSON with
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* 2-space indent (matches the file's existing style).
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*/
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function setServerEnabled(serverName: string, enabled: boolean): void {
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const raw = fs.readFileSync(SETTINGS_PATH, "utf8");
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const parsed = JSON.parse(raw);
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if (!parsed.mcp || !parsed.mcp[serverName]) {
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throw new Error(`server '${serverName}' not in settings.json`);
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}
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if (enabled) {
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// Default is true — clear the explicit flag if present, keep the file tidy.
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delete parsed.mcp[serverName].enabled;
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} else {
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parsed.mcp[serverName].enabled = false;
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}
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fs.writeFileSync(SETTINGS_PATH, `${JSON.stringify(parsed, null, 2)}\n`, "utf8");
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}
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// ── Per-server runtime state (for /mcp display) ──────────────────────────────
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type ServerRuntimeState =
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| { kind: "running"; toolCount: number }
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| { kind: "failed"; message: string }
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| { kind: "disabled" }
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| { kind: "remote-skipped" }
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| { kind: "invalid"; message: string };
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// ── Extension entry ──────────────────────────────────────────────────────────
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export default async function mcpLoaderExtension(pi: ExtensionAPI) {
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const servers = readMcpServers();
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const runtime = new Map<string, ServerRuntimeState>();
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const clients: StdioMcpClient[] = [];
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// Always register /mcp — even when no servers are configured, so users
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// discover the surface. Handler reads settings.json fresh on each invoke.
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registerMcpCommand(pi, runtime);
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if (Object.keys(servers).length === 0) {
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dlog("no MCP servers configured — nothing to load");
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return;
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}
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for (const [name, cfg] of Object.entries(servers)) {
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if (cfg.enabled === false) {
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dlog(`${name}: disabled in settings.json, skipping`);
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runtime.set(name, { kind: "disabled" });
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continue;
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}
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if (cfg.type === "remote") {
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warn(
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`${name}: remote MCP transport not yet supported by mcp-loader (v1 is stdio-only); skipping`,
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);
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runtime.set(name, { kind: "remote-skipped" });
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continue;
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}
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const local = cfg as LocalServerConfig;
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if (!Array.isArray(local.command) || local.command.length === 0) {
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warn(`${name}: invalid \`command\` (must be non-empty array), skipping`);
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runtime.set(name, { kind: "invalid", message: "command must be non-empty array" });
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continue;
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}
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const [bin, ...args] = local.command;
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const client = new StdioMcpClient(name);
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try {
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await client.start(bin, args, local.env);
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} catch (err) {
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const message = (err as Error).message;
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warn(`${name}: failed to start — ${message}`);
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runtime.set(name, { kind: "failed", message });
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client.stop();
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continue;
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}
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dlog(`${name}: connected, ${client.tools.length} tools`);
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runtime.set(name, { kind: "running", toolCount: client.tools.length });
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clients.push(client);
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// Register each MCP tool as a pi tool.
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for (const tool of client.tools) {
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const piName = namespacedToolName(name, tool.name);
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const schema =
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tool.inputSchema && typeof tool.inputSchema === "object"
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? (Type.Unsafe<Record<string, unknown>>(
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tool.inputSchema as object,
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) as unknown as ReturnType<typeof Type.Object>)
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: Type.Object({}, { additionalProperties: true });
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pi.registerTool({
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name: piName,
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label: piName,
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description: tool.description ?? `MCP tool from ${name}`,
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parameters: schema,
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async execute(_toolCallId, params) {
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try {
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const result = await client.callTool(tool.name, params as Record<string, unknown>);
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const text = extractText(result);
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return {
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content: [{ type: "text", text }],
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details: { server: name, tool: tool.name, raw: result },
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};
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} catch (err) {
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return {
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content: [
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{
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type: "text",
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text: `MCP call failed (${name}/${tool.name}): ${(err as Error).message}`,
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},
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],
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details: { server: name, tool: tool.name, error: (err as Error).message },
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isError: true,
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};
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}
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},
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});
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}
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}
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// Tear down subprocesses on session shutdown so reloads don't leak procs.
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pi.on("session_shutdown", async () => {
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for (const c of clients) c.stop();
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});
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}
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// ── /mcp slash command ──────────────────────────────────────────────────────
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const VAL_ON = "● enabled";
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const VAL_OFF = "○ disabled";
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const VAL_RO = "[read-only]";
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function statusLabel(state: ServerRuntimeState | undefined, configEnabled: boolean): string {
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if (!state) return configEnabled ? "unknown" : "disabled";
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switch (state.kind) {
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case "running":
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return `running · ${state.toolCount} tool${state.toolCount === 1 ? "" : "s"}`;
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case "failed":
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return `failed: ${state.message}`;
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case "disabled":
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return "disabled in settings";
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case "remote-skipped":
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return "remote (skipped — v1 stdio only)";
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case "invalid":
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return `invalid: ${state.message}`;
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}
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}
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function registerMcpCommand(pi: ExtensionAPI, runtime: Map<string, ServerRuntimeState>) {
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pi.registerCommand("mcp", {
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description: "List and toggle MCP servers configured in ~/.pi/agent/settings.json",
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handler: async (_args, ctx) => {
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const servers = readMcpServers();
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const names = Object.keys(servers);
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if (names.length === 0) {
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ctx.ui.notify(
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`No MCP servers configured. Add an \`mcp\` block to ${SETTINGS_PATH}.`,
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"info",
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);
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return;
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}
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// Snapshot config-level enabled state (default true if unset).
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const configEnabled = new Map<string, boolean>();
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for (const [n, cfg] of Object.entries(servers)) {
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configEnabled.set(n, cfg.enabled !== false);
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}
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// Staged state: name → enabled (initialised from configEnabled).
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const staged = new Map(configEnabled);
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await ctx.ui.custom<void>((tui, theme, _kb, done) => {
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let statusText = "";
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const items: SettingItem[] = names.map((n) => {
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const cfg = servers[n];
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const cfgEn = configEnabled.get(n) ?? true;
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const state = runtime.get(n);
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const isRemote = cfg.type === "remote";
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const isInvalid = state?.kind === "invalid";
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const transport = isRemote ? "remote" : "local";
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const desc = `${transport} · ${statusLabel(state, cfgEn)}`;
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if (isInvalid) {
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return {
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id: n,
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label: n,
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currentValue: VAL_RO,
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description: desc,
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};
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}
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return {
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id: n,
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label: n,
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currentValue: cfgEn ? VAL_ON : VAL_OFF,
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values: [VAL_ON, VAL_OFF],
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description: desc,
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};
|
|
});
|
|
|
|
const container = new Container();
|
|
|
|
container.addChild({
|
|
render(_w: number) {
|
|
return [
|
|
theme.fg("accent", theme.bold("MCP servers — settings.json `mcp` block")),
|
|
theme.fg(
|
|
"muted",
|
|
" space: toggle (stage) · enter: apply + reload · esc: cancel",
|
|
),
|
|
"",
|
|
];
|
|
},
|
|
invalidate() {},
|
|
});
|
|
|
|
const settingsList = new SettingsList(
|
|
items,
|
|
Math.min(items.length + 2, 20),
|
|
getSettingsListTheme(),
|
|
(id, newValue) => {
|
|
const isInvalid = runtime.get(id)?.kind === "invalid";
|
|
if (isInvalid) {
|
|
settingsList.updateValue(id, VAL_RO);
|
|
statusText = `⊘ ${id}: invalid config — fix in settings.json`;
|
|
tui.requestRender();
|
|
return;
|
|
}
|
|
const stagingEnabled = newValue === VAL_ON;
|
|
staged.set(id, stagingEnabled);
|
|
|
|
const drift: string[] = [];
|
|
for (const n of names) {
|
|
const s = staged.get(n);
|
|
const c = configEnabled.get(n);
|
|
if (s !== undefined && s !== c) drift.push(`${n}→${s ? "on" : "off"}`);
|
|
}
|
|
statusText = drift.length ? `pending: ${drift.join(", ")}` : "";
|
|
tui.requestRender();
|
|
},
|
|
() => {
|
|
done(undefined);
|
|
},
|
|
);
|
|
|
|
container.addChild(settingsList);
|
|
|
|
container.addChild({
|
|
render(_w: number) {
|
|
if (!statusText) return [""];
|
|
const colored = statusText.startsWith("⊘")
|
|
? theme.fg("warning", statusText)
|
|
: theme.fg("muted", statusText);
|
|
return ["", colored];
|
|
},
|
|
invalidate() {},
|
|
});
|
|
|
|
return {
|
|
render(width: number) {
|
|
return container.render(width);
|
|
},
|
|
invalidate() {
|
|
container.invalidate();
|
|
},
|
|
handleInput(data: string) {
|
|
if (matchesKey(data, Key.enter)) {
|
|
const errors: string[] = [];
|
|
let applied = 0;
|
|
for (const n of names) {
|
|
const s = staged.get(n);
|
|
const c = configEnabled.get(n);
|
|
if (s === undefined || s === c) continue;
|
|
try {
|
|
setServerEnabled(n, s);
|
|
applied++;
|
|
} catch (err) {
|
|
const msg = err instanceof Error ? err.message : String(err);
|
|
errors.push(`${n}: ${msg}`);
|
|
}
|
|
}
|
|
done(undefined);
|
|
if (errors.length) {
|
|
ctx.ui.notify(`mcp: ${errors.join(" | ")}`, "error");
|
|
} else if (applied > 0) {
|
|
ctx.ui.notify(`mcp: applied ${applied} change(s); reloading…`, "info");
|
|
ctx.reload().catch((err) => {
|
|
const msg = err instanceof Error ? err.message : String(err);
|
|
ctx.ui.notify(`reload failed: ${msg}`, "error");
|
|
});
|
|
}
|
|
return;
|
|
}
|
|
settingsList.handleInput?.(data);
|
|
tui.requestRender();
|
|
},
|
|
};
|
|
});
|
|
},
|
|
});
|
|
}
|