Watch

What It Does

Files on a mounted backend change outside your workspace all the time: a teammate uploads to Nextcloud, a pipeline rewrites an S3 object, a cron job deletes a report. watch turns those external changes into an async event stream, so an agent reacts instead of rescanning and diffing directories.

from mirage import Workspace
from mirage.resource.nextcloud import NextcloudConfig, NextcloudResource

ws = Workspace({"/nc": NextcloudResource(NextcloudConfig(...))})

async for event in ws.watch("/nc/Documents"):
    print(event.kind, event.path.virtual)   # e.g. "update /nc/Documents/report.txt"
    result = await ws.execute(f"cat {event.path.virtual}")  # guaranteed fresh

No setup call is needed: the watch runtime attaches lazily on first use, and an idle workspace carries no watch state at all. Mirage runs no server and no background loop. Detection is yours (a webhook receiver or a small poll loop); Mirage’s job is everything after the signal: cache invalidation, scope matching, and delivery.

Scopes

The root’s shape defines the depth, GNU shell glob style. * never crosses /, and matching happens at delivery time, so files created after the watch started still match.

root	scope
`/nc/data`	the whole subtree
`/nc/data/*`	the entries at that level only (shallow, no descent)
`/nc/data/*/`	everything inside child directories (GNU `*/` matches directories)
`/nc/data/*.txt`	the `.txt` entries at that level
`/nc/data/*/reports/`	everything inside each child’s `reports` directory
`["/nc/docs", "/nc/cfg/app.yaml"]`	any of several roots, one event stream

async for event in ws.watch("/nc/data/*.pdf"):   # pattern
    ...

async for event in ws.watch(["/nc/inbox/*", "/nc/config"]):  # list
    ...

The Event

@dataclass(frozen=True, slots=True)
class FileEvent:
    kind: FileChangeKind                   # create / update / delete / move / unknown
    path: PathSpec                         # virtual path of the changed entry
    timestamp: datetime                    # UTC time the change was observed
    previous_path: PathSpec | None = None  # prior path for MOVE events
    metadata: FileMetadata | None = None   # post-change metadata, when the source has it

FileMetadata carries fingerprint (the backend’s ETag/rev, or an mtime|size composite), size, and modified. Producers fill only what their signal honestly knows: a listing walk fills all three, a webhook payload none. unknown is the overflow signal: if a burst exceeds the queue cap, pending events collapse into one unknown event per watch root, meaning “re-inventory this subtree”. Precision degrades; dirtiness is never lost. Events are level-triggered: an event says what is dirty, not every intermediate edit. Read current content through the workspace after receiving one. That read is guaranteed fresh, because Mirage invalidates the changed path’s cache entries, and every cached ancestor listing up to the mount root, before the event reaches any subscriber.

Push Mode

Host a small endpoint in your own service, map the provider payload to a FileEvent, and inject it with ws.notify. For Nextcloud, the webhook_listeners app (Nextcloud 30+) POSTs on every file event:

async def handle(request):                     # your aiohttp/FastAPI route
    payload = await request.json()
    kind = KIND_BY_CLASS.get(payload["event"]["class"])   # NodeCreatedEvent -> create ...
    node = payload["event"]["node"]["path"]               # /admin/files/data/report.txt
    virtual = "/nc/" + node.removeprefix("/admin/files/") # -> /nc/data/report.txt
    await ws.notify(FileEvent(kind=kind,
                              path=PathSpec.from_str_path(virtual),
                              timestamp=datetime.now(timezone.utc)))
    return web.json_response({"ok": True})

The full runnable version, including the one-time occ registration commands, is examples/python/nextcloud/watch.py.

Pull Mode

Backends that implement delta_hook() (Nextcloud today) answer one question: what changed under this root since the last checkpoint? A baseline pull (checkpoint=None) emits nothing; every later pull diffs against the checkpoint you hand back. The whole consumer poller is:

hook = ws.registry.mount_for("/nc").resource.delta_hook()
checkpoint = None
while True:
    delta = await hook.pull(root, checkpoint)
    checkpoint = delta.checkpoint
    for event in delta.changes:
        await ws.notify(event)
    await asyncio.sleep(30)

Pull is self-healing: it diffs current backend state against your checkpoint, so events missed while your service was down surface on the next pull. A common production shape is push-first with a pull at startup as recovery, or webhook-as-doorbell: on any webhook, pump the pull once and trust its diff rather than the payload.

Queues

Each watch() owns its own delivery queue: notify fans one event out into every queue whose scope matches, so two watches on overlapping scopes each consume at their own pace and a slow consumer only overflows its own queue. The default RAMWatchQueue coalesces per path with level-triggered semantics (create then update stays create; create then delete cancels; delete then create becomes update), so pending size is bounded by distinct dirty paths, not event volume. Overflow policy is collapse (default, the unknown rescan event), drop_oldest, or error. To customize, attach the runtime explicitly before the first watch:

from functools import partial
from mirage.watch import RAMWatchQueue, Watcher

ws.attach_watch_runtime(
    Watcher(ws.registry,
            queue_factory=partial(RAMWatchQueue, max_pending=64)))

Any object satisfying the async WatchQueue protocol (push / pop / pending / clear / close) drops in, so a Redis- or SQS-backed queue needs no interface changes. See examples/python/nextcloud/watch_custom_queue.py for a runnable custom-queue setup. To tear down without closing the workspace, await ws.detach_watch_runtime(): every subscriber queue closes (active watch loops end cleanly) and the workspace returns to its idle state; the next watch lazily attaches a fresh default runtime.

Scope Notes

Watch roots are fixed at subscription time: there is no API to add or remove roots on a live watch. To change scope, start a new watch() with the updated list and stop iterating the old one (its pending events are dropped when it closes). A mutable subscription handle is future work.
A watch may span mounts, including a mount nested inside another mount’s subtree: scope matching is on virtual paths, and each event is invalidated on the mount that owns its path (longest prefix). Detection stays per backend, so each mount needs its own signal feeding ws.notify.
Python only for now; the TypeScript mirror is planned.
Nextcloud is the first backend with a delta_hook; push mode works with any backend today since ws.notify accepts events from any detection you run. See the Watch Matrix for per-resource support.
Events are in-memory and at-most-once per subscriber; durable queues and acknowledgement are future work.

Getting Started

Agents

Resources

Runtimes

Watch

What It Does

Scopes

The Event

Push Mode

Pull Mode

Queues

Scope Notes

​What It Does

​Scopes

​The Event

​Push Mode

​Pull Mode

​Queues

​Scope Notes

What It Does

Scopes

The Event

Push Mode

Pull Mode

Queues

Scope Notes