stack/packages/discord/tests/fake-pi.mjs

// A stand-in for `pi --mode rpc`. Reads JSONL commands on stdin, writes
// events on stdout. Behaviour is scripted per prompt text:
//   "slow <ms>"   answer "slow reply" after <ms>
//   "garbage"     emit one malformed line
//   "error"       end the turn with stopReason error
//   "tools <n>"   a first turn that calls <n> tools (read_file, with a
//                 tool_execution_start/end pair each, the last one refused),
//                 then a second turn that answers "read <n> file(s)"
//   "toolonly"    a run whose only turn calls a tool and never answers
//   "retry"       an agent_end with willRetry, then the real answer
//   "mute"        accept the prompt and emit nothing, staying idle
//   "late <ms>"   ignore abort; after <ms> emit a tool pair and a tool turn,
//                 then answer "late reply", like a run that outlives its
//                 client-side timeout
//   "stall <ms>"  accept the prompt, then read nothing for <ms> (pi stuck
//                 before agent_start); then run it, answering "echo:
//                 stalled", and only then read what came in meanwhile
//   anything else answer "echo: <text>" immediately
// A prompt received while busy without streamingBehavior is refused, as pi
// does. A prompt with streamingBehavior followUp is folded into the running
// loop as real pi does: answered inside the same run, one agent_end for
// both, no agent_start of its own. The engine must therefore never send
// one; this fake makes that visible. Every command is mirrored to
// FAKE_PI_LOG when set.
import { appendFileSync } from "node:fs";

const logPath = process.env.FAKE_PI_LOG;
const out = (o) => process.stdout.write(JSON.stringify(o) + "\n");
let busy = false;
const queue = [];

function assistant(text, stopReason = "stop") {
  return { role: "assistant", content: text === null ? [] : [{ type: "text", text }], stopReason, usage: { input: 3, output: 2 }, model: "fake", provider: "fake" };
}

function run(text) {
  if (text === "mute") return;
  busy = true;
  out({ type: "agent_start" });
  out({ type: "turn_start" });
  const finish = (message) => {
    out({ type: "turn_end", message, toolResults: [] });
    out({ type: "agent_end", messages: [message] });
    if (queue.length > 0) {
      // Real pi: the follow-up continues this run; both answers are inside
      // it and agent_end above already covered them. Just settle.
      queue.length = 0;
    }
    busy = false;
    out({ type: "agent_settled" });
  };
  const tm = /^tools (\d+)$/.exec(text);
  if (tm || text === "toolonly") {
    const n = tm ? Number(tm[1]) : 1;
    const calls = [];
    for (let i = 1; i <= n; i += 1) {
      const id = `call_${i}`;
      const last = i === n && n > 1;
      calls.push({ type: "toolCall", id, name: "read_file", arguments: { root: "docs", path: `f${i}.md` } });
      out({ type: "tool_execution_start", toolCallId: id, toolName: "read_file", args: { root: "docs", path: `f${i}.md` } });
      out({ type: "tool_execution_end", toolCallId: id, toolName: "read_file", isError: false, result: { content: [{ type: "text", text: last ? "refused: budget" : "1: hello" }], details: last ? { tool: "read_file", root: "docs", path: `f${i}.md`, ok: false, reason: "tool budget for this message is used up", ms: 1 } : { tool: "read_file", root: "docs", path: `f${i}.md`, ok: true, bytes: 9, ms: 2 } } });
    }
    const toolTurn = { role: "assistant", content: calls, stopReason: "toolUse", usage: { input: 3, output: 2 }, model: "fake", provider: "fake" };
    out({ type: "turn_end", message: toolTurn, toolResults: [] });
    if (text === "toolonly") {
      out({ type: "agent_end", messages: [toolTurn] });
      busy = false;
      out({ type: "agent_settled" });
      return;
    }
    out({ type: "turn_start" });
    const answer = assistant(`read ${n} file(s)`);
    out({ type: "turn_end", message: answer, toolResults: [] });
    out({ type: "agent_end", messages: [toolTurn, answer] });
    queue.length = 0;
    busy = false;
    out({ type: "agent_settled" });
    return;
  }
  const lm = /^late (\d+)$/.exec(text);
  if (lm) {
    setTimeout(() => {
      const args = { root: "docs", path: "late.md" };
      out({ type: "tool_execution_start", toolCallId: "call_late", toolName: "read_file", args });
      out({ type: "tool_execution_end", toolCallId: "call_late", toolName: "read_file", isError: false, result: { content: [{ type: "text", text: "1: late" }], details: { tool: "read_file", ...args, ok: true, bytes: 5, ms: 1 } } });
      out({ type: "turn_end", message: { role: "assistant", content: [{ type: "toolCall", id: "call_late", name: "read_file", arguments: args }], stopReason: "toolUse", usage: { input: 3, output: 2 }, model: "fake", provider: "fake" }, toolResults: [] });
      out({ type: "turn_start" });
      finish(assistant("late reply"));
    }, Number(lm[1]));
    return;
  }
  if (text === "retry") {
    out({ type: "agent_end", messages: [], willRetry: true });
    finish(assistant("after retry"));
    return;
  }
  const m = /^slow (\d+)$/.exec(text);
  if (m) {
    const timer = setTimeout(() => finish(assistant("slow reply")), Number(m[1]));
    current = { timer, finish };
    return;
  }
  if (text === "garbage") {
    process.stdout.write("this is not json\n");
    finish(assistant("after garbage"));
    return;
  }
  if (text === "error") {
    finish({ ...assistant(null, "error"), errorMessage: "fake provider error" });
    return;
  }
  finish(assistant(`echo: ${text}`));
}
let current = null;

let buffer = "";
let stalled = false;
process.stdin.setEncoding("utf8");
process.stdin.on("data", (chunk) => {
  buffer += chunk;
  drain();
});

function drain() {
  let idx;
  while (!stalled && (idx = buffer.indexOf("\n")) !== -1) {
    const line = buffer.slice(0, idx);
    buffer = buffer.slice(idx + 1);
    if (!line) continue;
    const cmd = JSON.parse(line);
    if (logPath) appendFileSync(logPath, line + "\n");
    if (cmd.type === "prompt") {
      if (busy && !cmd.streamingBehavior) {
        out({ id: cmd.id, type: "response", command: "prompt", success: false, error: "agent is streaming; specify streamingBehavior" });
        continue;
      }
      out({ id: cmd.id, type: "response", command: "prompt", success: true });
      const sm = /^stall (\d+)$/.exec(cmd.message);
      if (sm) {
        stalled = true;
        setTimeout(() => {
          run("stalled");
          stalled = false;
          drain();
        }, Number(sm[1]));
      } else if (busy) queue.push(cmd.message);
      else run(cmd.message);
    } else if (cmd.type === "abort") {
      out({ id: cmd.id, type: "response", command: "abort", success: true });
      if (current) {
        clearTimeout(current.timer);
        const f = current.finish;
        current = null;
        f(assistant("", "aborted"));
      }
    } else {
      out({ id: cmd.id, type: "response", command: cmd.type, success: true, data: {} });
    }
  }
}
process.stdin.on("end", () => process.exit(0));