116 lines
4.8 KiB
Markdown
116 lines
4.8 KiB
Markdown
# Media scraper
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The scrape engine walks a channel's history and fills a per-scrape database. It is backend
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agnostic: slopbot for guild channels, the puppet's core bridge for everything including group DMs.
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See [slopbot.md](slopbot.md) and [core-bridge.md](core-bridge.md).
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## Backends
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Both backends implement one interface:
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```ts
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interface ScrapeBackend {
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fetchPage(channelId: string, before: string | null, limit: number):
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Promise<{ messages: RawMessage[]; rateLimited?: { retryAfterMs: number } }>;
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}
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```
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| Backend | Implementation |
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| --- | --- |
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| `slopbot` | discord.js REST (`channels.messages.fetch`), bucket-aware client |
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| `puppet` | The core action `message.fetch` over the bridge |
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The daemon picks `slopbot` when the channel is a guild channel and slopbot is configured and in the
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guild; otherwise `puppet`. A scrape records the backend it used. The walk can resume on the same
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backend only.
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## Walk
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1. The command resolves the channel and creates a scrape directory.
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2. Newest to oldest: fetch `limit` messages before the cursor. The cursor is the oldest message ID
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seen.
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3. Extract media from each message and write the page to the database in one transaction.
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4. Persist `scrape.json` (cursor, counters, state) after every page.
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5. Stop when a page returns fewer than `limit` messages or the oldest message is reached.
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6. Resume after a daemon restart from the stored cursor.
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Rules:
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- One running scrape at a time. Further requests queue.
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- `stop` marks the job and lets the current page finish.
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- Every page is an outbound read. Sends from commands keep their own pacing.
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## Pacing and backoff
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The engine is deliberately slower than normal reads. All values are configurable; defaults are
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starting points, not Discord facts.
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| Setting | Default |
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| --- | --- |
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| `media.pageMinMs` / `media.pageMaxMs` | 1200 / 3500 |
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| `media.pagesPerHour` | 300 |
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| `media.pagesPerDay` | 3000 |
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| `media.maxRetries` | 8 |
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- A random gap in the page window between pages.
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- A rolling budget per hour and per day. At the cap the job pauses and resumes when the window
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resets.
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- On failure: use the backend's `retryAfterMs` when present, else exponential `2^attempt + 1`
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seconds, matching DiscordChatExporter. After `maxRetries` the job pauses instead of looping.
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- DiscordChatExporter treats user-token limits more carefully than bot limits. The puppet backend
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uses the slower schedule and the tighter budgets; slopbot can run faster and lets discord.js
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handle buckets.
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## Classification
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The extractor maps one message to zero or more media items and returns their kind, source URL,
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provider, dimensions, duration when known, and size when known.
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- Attachments from `attachments[]`: extension and `contentType` decide image, gif, video, audio.
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- Embeds from `embeds[]`: `type` and `provider` decide. `video` embeds become kind `video` with
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`downloaded = false`. Image and gif embeds become cached previews only.
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- Forwarded message snapshots are treated as messages with their own media.
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- Stickers become images or gifs.
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- Voice messages (`voiceMessage` flag) become audio.
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- Third-party embeds are never downloaded, by rule.
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## Database schema
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One SQLite file per scrape (`index.db`, `node:sqlite`).
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| Table | Columns |
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| --- | --- |
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| `messages` | `id`, `author_id`, `author_name`, `timestamp`, `content` |
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| `media` | `id`, `kind`, `url`, `provider`, `file_hash`, `preview_hash`, `content_type`, `size`, `width`, `height`, `duration_ms`, `downloaded`, `created_at` |
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| `media_sources` | `media_id`, `message_id` |
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| `downloads` | `media_id`, `state`, `attempts`, `error` |
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Indexes: `(kind, timestamp)` via `media_sources`, `channel` metadata in `scrape.json`, and
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`file_hash` for dedupe. The database is an index; the media folder holds bytes.
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## Downloads and previews
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- `downloads` is a serial queue, one file at a time, 1-3 s apart, with a size cap
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(`media.maxFileBytes`, default 50 MiB) and 2 retries on network or 5xx errors.
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- `4xx` marks the URL expired. The item is re-fetched with its message later.
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- Previews use the Discord CDN resizer (`?width=320&height=320&format=webp`) and are stored by hash
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in `thumbs/`. A preview failure never fails the scrape.
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## Job states
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`queued`, `running`, `paused`, `stopping`, `done`, `failed`, `pending-delete`, `deleting`, `deleted`.
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Counters: pages, messages, media by kind, downloaded bytes, preview bytes, errors. The Media tab
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and the MCP `get_media_scrape` tool read the same fields.
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## Tests
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- Unit tests run against the mock core and a fake slopbot REST. No live Discord.
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- Fixtures cover each media kind, forwards, voice messages, expired URLs, and 429 backoff.
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- The live run is a private test guild first, then a real channel.
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## Checkpoints
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Implementation goals live in [CURRENT.md](../CURRENT.md). The engine is C3; slopbot is C4; daemon
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wiring (command, service, routes) is C5.
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