162 lines
8.3 KiB
Markdown
162 lines
8.3 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. A to-date sets the starting cursor; a from-date trims each page and ends the walk when the
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boundary is crossed (`afterId`/`beforeId` in the meta).
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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`, `source`, `author_id`, `author_name`, `posted_at`, `url`, `provider`, `file_hash`, `preview_hash`, `content_type`, `size`, `width`, `height`, `aspect_ratio`, `duration_secs`, `downloaded`, `file_path`, `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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`scrape.json` also records `fromDate`/`toDate`, and `estimatedMessages` from Discord search when the
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slopbot backend could ask for it (one request; null otherwise). Indexes: `kind`, `posted_at`, and
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`media_sources(message_id)`. The database is an index; the media
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folder holds bytes. Every item carries its poster (`author_id`, `author_name`), the post time
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(`posted_at`), and its dimensions (`width`, `height`, `aspect_ratio`). Filter presets live in
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`media-scrape/src/filter-presets.ts`: aspect buckets (vertical, square, 4:3, 16:9, 21:9, other) and
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resolution buckets by the shortest side (SD, HD, FHD, QHD, 4K+, unknown). A missing resolution is
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filled with `ffprobe` after a download when `VESKSLOP_FFPROBE` is available.
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## Downloads and previews
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Downloads run after a finished walk when the scrape used `mode: "download"`:
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- A serial queue, one file at a time, 1-3 s apart, with a size cap
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(`VESKSLOP_MEDIA_MAX_FILE_BYTES`, default 50 MiB) and 2 retries on network or 5xx errors.
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- `4xx` from the skip set (400, 401, 403, 404, 410) marks the URL expired; the row is not retried.
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- The file name is the SHA-256 of the bytes under `media/`. `file_path`, `file_hash`, and
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`file_bytes` are written to the row, so the run resumes and dedupes by content.
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- Only attachment and sticker rows are targets. Embed rows are excluded in SQL
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(`source != 'embed'`).
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- With a custom destination, files go to `<destination>/<scrape-id>/media/` and the row stores the
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absolute path; without one they stay in `<scrape>/media/`. Embed previews are copied to
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`<destination>/<scrape-id>/thumbnails/` while the local copy stays for the Media tab.
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- Downloaded videos get a poster frame (`ffmpeg -ss 0.5`, 480px WebP) cached in `thumbs/`, because
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Discord serves no thumbnails for uploaded video files.
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- The ffprobe pass fills missing dimensions and `duration_secs` after a download. Attachment
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durations come from Discord; the 0 that Discord sends for non-audio files is treated as unknown.
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- Progress counters: `downloaded`, `downloadErrors`.
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Previews run after every walk:
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- In both modes, Discord-hosted image, GIF, and **video** URLs (`cdn.discordapp.com`,
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`media.discordapp.net`) are transformed to the CDN resizer
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(`media.discordapp.net?...width=320&height=320&format=webp`). The proxy renders a frame for
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video files, so attachment mp4/webm get a cached poster in links mode without downloading the
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file. Download mode additionally keeps an ffmpeg poster.
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- In both modes, embed rows also get their stored `preview_url` (YouTube, X, TikTok thumbnails,
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and so on) cached. The embed's full media URL is never fetched; embed rows are excluded from
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`pendingDownloads`.
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- Embeds without a thumbnail in Discord's data (fxtwitter, vxReddit, ...) are resolved first:
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provider oEmbed/fxtwitter API, then the page's `og:image`/`twitter:image` (512 KiB read cap,
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10 s timeout, one attempt).
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- Animated GIF previews are stored as a static first frame (`ffmpeg`, 480px WebP); the original
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animated GIF URL stays in `preview_url` for hover playback. Tenor embeds without a thumbnail are
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resolved through Tenor's oEmbed.
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- One attempt per row, no retries; a failure marks `preview_error` and never fails the scrape.
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- Stored by hash in `thumbs/<sha256>.<ext>`, where the extension follows the response type
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(`preview_ext`, default webp); `preview_hash` and `preview_bytes` land on the row, and the
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counter is `previewed`. Previews count toward the storage limit.
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- The job stays `running` through the download and preview passes, so a client never sees `done`
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on a half-archived scrape. A paused walk still gets these passes for the pages it collected.
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- At daemon start, `backfillPreviews` runs the same pass over scrapes that paused before their
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previews were cached, so a stopped scrape does not leave blank tiles.
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- Preview gaps default to 200-600 ms (`VESKSLOP_MEDIA_PREVIEW_MIN_MS`/`_MAX_MS`), much faster than
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file downloads.
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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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