feat: image variants engine

docs/configuration.md

@@ -34,6 +34,9 @@ Copy [`.env.example`](../.env.example) to `.env` to get started. When a required
 | `AUTH_RATE_LIMIT_WINDOW_SECONDS` | `60`        | Length, in seconds, of the fixed rate-limit window for the routes above.                                                                                                                                                    |
 | `TRUSTED_PROXIES`      | *(empty)*            | Semicolon-separated list of exact IP addresses (no CIDR) of reverse proxies allowed to supply the client IP via `X-Real-IP` for the rate limiting of the routes above. When a request's connection address is not in this list, any `X-Real-IP` or `X-Forwarded-For` header it sends is ignored and the connection address is used instead. See [deployment.md](deployment.md).      |
 | `RENEWCMS_CONTAINER` | `false` | Set to `true` (case-insensitive; any other value means `false`) when the app runs in a container. Settings then tells the owner to update by pulling a new image instead of offering browser updates, and `can_apply` is always `false`. The Dockerfile and `docker-compose.yml` set it to `true`. Update checks still work. |
+| `IMAGE_VARIANT_MAX_SOURCE_BYTES` | `10485760` | Largest stored image, in bytes, that an [image variant](image-variants.md) may be generated from. A request for a bigger source answers 413 with a plain-text body. The original is never affected, and SVG and animated GIF are always served as they are. A value that is not a whole number greater than zero stops the server at boot with an error naming the variable. |
+| `IMAGE_VARIANT_MAX_SOURCE_PIXELS` | `50000000` | Largest declared width x height, in pixels, that an [image variant](image-variants.md) may be generated from. It is read from the image header before any pixel buffer is allocated; a bigger source answers 413 with the same plain-text body as the byte cap. The original is never affected, and SVG and animated GIF are always served as they are. A value that is not a whole number greater than zero stops the server at boot with an error naming the variable. |
+| `IMAGE_VARIANT_MAX_CONCURRENT_RENDERS` | `4` | Number of [image variant](image-variants.md) renders that may run at once. Other requests wait for a free slot until their client goes away; cached files never wait. A value that is not a whole number greater than zero stops the server at boot with an error naming the variable. |
 | `UPDATE_FEED_URL`      | `https://git.floriansylvain.fr` | Base URL of the Gitea server that publishes RenewCMS releases. The Settings page asks `{UPDATE_FEED_URL}/api/v1/repos/fsylvain/RenewCMS/releases` when the owner checks for updates. The last result is kept in `update-status.json`, in the data directory. |
 
 Automatic media purge has no environment variable. Its schedule (on or off, interval, `enabled_at`, `last_purge_at`) lives in the purge settings row of the database, is changed from the Settings page or `PATCH /v1/media/purge-settings`, and is read again at every hourly tick.