app/backend/fluksio/api/routes/workers.py

"""Remote workers: how one attaches, and what is attached right now.

A worker dials in rather than being dialled: the GPU box and the engine are
usually on different networks, and only one of them can be reached. It presents
a token minted here, says what it can do, and then answers calls on the socket
it opened.
"""

from __future__ import annotations

import asyncio
import logging
from datetime import timedelta
from typing import Any

from fastapi import APIRouter, Depends, HTTPException, Request, WebSocket
from fastapi.responses import PlainTextResponse
from fluksio_worker import worker_main
from jwt.exceptions import InvalidTokenError
from pydantic import BaseModel, Field

from fluksio.api.deps import get_current_active_superuser, get_current_user
from fluksio.core import security
from fluksio.flow.remote import PROTOCOL, RemoteWorker, RemoteWorkerHub

logger = logging.getLogger(__name__)

router = APIRouter(prefix="/workers", tags=["workers"])

#: Long, because a worker is a machine somebody set up once and left running.
TOKEN_DAYS = 365


class WorkerInfo(BaseModel):
    name: str
    labels: list[str] = Field(default_factory=list)
    max_parallel: int = 1
    in_flight: int = 0
    attached_at: float = 0.0
    last_seen: float = 0.0
    python: str = ""
    venv_digest: str = ""


class TokenRequest(BaseModel):
    name: str


class TokenIssued(BaseModel):
    name: str
    token: str
    expires_days: int = TOKEN_DAYS


def _hub(app: Any) -> RemoteWorkerHub:
    hub: RemoteWorkerHub | None = getattr(app.state, "worker_hub", None)
    if hub is None:
        raise HTTPException(status_code=503, detail="Remote workers are not available")
    return hub


@router.get(
    "", response_model=list[WorkerInfo], dependencies=[Depends(get_current_user)]
)
def read_workers(request: Request) -> Any:
    """What is attached, and how busy it is."""
    return [
        WorkerInfo(
            name=worker.name,
            labels=sorted(worker.labels),
            max_parallel=worker.max_parallel,
            in_flight=worker.in_flight,
            attached_at=worker.attached_at,
            last_seen=worker.last_seen,
            python=str(worker.info.get("python") or ""),
            venv_digest=str(worker.info.get("venv_digest") or ""),
        )
        for worker in _hub(request.app).workers()
    ]


@router.post(
    "/tokens",
    response_model=TokenIssued,
    dependencies=[Depends(get_current_active_superuser)],
)
def issue_token(body: TokenRequest) -> Any:
    """Mint the credential a worker presents when it dials in.

    Shown once. It is signed with the same keypair the agent tokens use, so
    rotating that key revokes every worker along with them.
    """
    token = security.create_worker_token(body.name, timedelta(days=TOKEN_DAYS))
    return TokenIssued(name=body.name, token=token)


@router.get(
    "/runtime",
    response_class=PlainTextResponse,
    dependencies=[Depends(get_current_user)],
)
def read_runtime() -> str:
    """The worker's own code, so a fresh host installs by fetching one file.

    It is the same module the engine's local workers run — deliberately
    standard library only, and with nothing of the engine importable in it.
    """
    return worker_main.__file__ and open(worker_main.__file__).read()


@router.websocket("/attach")
async def attach(websocket: WebSocket, token: str = "") -> None:
    """A worker's connection, for as long as it holds.

    The token goes in the query string for the same reason the dashboard's
    does: a websocket handshake carries no headers of its own.
    """
    try:
        claims = security.decode_worker_token(token)
    except InvalidTokenError:
        await websocket.close(code=1008)
        return

    await websocket.accept()
    try:
        hello = await asyncio.wait_for(websocket.receive_json(), timeout=30)
    except (TimeoutError, ValueError):
        await websocket.close(code=1002)
        return

    if hello.get("op") != "hello" or int(hello.get("protocol", 0)) != PROTOCOL:
        await websocket.send_json(
            {"op": "refused", "reason": f"this engine speaks protocol {PROTOCOL}"}
        )
        await websocket.close(code=1002)
        return

    # The token names the worker; what it calls itself is a suggestion, so two
    # hosts cannot fight over one identity by claiming the same name.
    name = str(claims.get("sub") or hello.get("name") or "worker")
    hub = _hub(websocket.app)
    worker = RemoteWorker(
        name=name,
        labels=[str(label) for label in (hello.get("labels") or [])],
        send=websocket.send_json,
        loop=asyncio.get_running_loop(),
        max_parallel=max(1, int(hello.get("max_parallel") or 1)),
        info={
            "python": hello.get("python"),
            "venv_digest": hello.get("venv_digest"),
        },
    )
    hub.attach(worker)
    await websocket.send_json({"op": "welcome", "protocol": PROTOCOL, "name": name})

    try:
        while True:
            message = await websocket.receive_json()
            worker.deliver(message)
    except Exception:
        # Any way this ends is the same thing: the socket is gone, and whatever
        # was waiting on it has to be told rather than left hanging.
        logger.info("Worker '%s' disconnected", name)
    finally:
        hub.detach(name)