# Change feed

The change feed a sync client polls: a start token, then changes.list from the saved token, one entry per changed file as the caller can read it.

The change feed lists each file that changed since a token, as the caller sees it, so a sync client can keep a local copy current without listing the whole Drive.

A sync client takes a start token first, lists what is already there with `files.list`, then polls `changes.list` from the saved token and keeps the token each answer hands back. Taking the token first means no write between the list and the token goes unseen:

```bash
AUTH='Authorization: Bearer ya29.placeholder'
TOKEN=$(curl -s -H "$AUTH" "$RYSTIC_URL/drive/v3/changes/startPageToken" | jq -r .startPageToken)
curl -s -H "$AUTH" -H 'Content-Type: application/json' -X PATCH -d '{"name":"beach-sunrise-v2.jpg"}' "$RYSTIC_URL/drive/v3/files/1MVjpgBeachSunrise03?fields=id,name" | jq -c .
# -> {"id":"1MVjpgBeachSunrise03","name":"beach-sunrise-v2.jpg"}
curl -s -H "$AUTH" "$RYSTIC_URL/drive/v3/changes?pageToken=$TOKEN" | jq -c '{newStartPageToken, changes: [.changes[] | {fileId, removed, name: .file.name}]}'
# -> {"newStartPageToken":"24","changes":[{"fileId":"1MVjpgBeachSunrise03","removed":false,"name":"beach-sunrise-v2.jpg"}]}
```

### One entry per file

A file created, renamed, moved, uploaded to, trashed, shared or unshared is listed once, holding its state when the page is read, however many times it changed since the token. A file the caller can no longer read, because it was deleted or unshared, is listed as `removed: true` with no `file`. A grant on a folder lists every file below it. Each caller's feed holds only what that caller can read: `X-Rystic-Actor` picks the caller ([Auth](https://www.rystic.ai/docs/simulators/google-drive.md#auth)).

### Pages

`pageSize` takes 1 to 1000 and defaults to 100; a value outside that range answers 400 `invalidParameter` at `page_size`. A page with more results carries `nextPageToken`: poll it next. The last page carries `newStartPageToken` instead: keep it and poll from it next time. Pick the next token by which member is present, not by how many entries came back. A request with no `pageToken` answers 400 `required`, and a token that is not a positive number 400 `invalid`.

### Timing and tokens

The simulator lists a change as soon as its write answers, where Drive lists it 1 to 4 seconds later, so a client that polls once right after a write passes here and can miss the change on Drive. Retry for a few seconds when you test against Drive.

Tokens count the simulator's own changes and keep counting across a reset or a scenario load, so a token never repeats and an older one lists only the changes made since. Treat a token as opaque and take it from `startPageToken` or `newStartPageToken`. A scenario's seeded files are not in the feed: take a start token, list them with `files.list`, then poll from the token.

Push notifications are not served: `changes.watch`, `files.watch` and `channels.stop` send to an address you register, so poll instead.

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Source: https://www.rystic.ai/docs/simulators/google-drive/features/change-feed · Markdown: https://www.rystic.ai/docs/simulators/google-drive/features/change-feed.md