132 lines
3.7 KiB
TypeScript
132 lines
3.7 KiB
TypeScript
/**
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* Shows the thumbnails a browser can't load from their own site: those on plain
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* http, which an https page would block, and those behind hotlink protection.
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* It fetches and caches the images `GET /api/proxy-image` serves, which the
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* frontend routes a thumbnail through when it is on http or when loading it
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* directly failed.
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*
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* @module
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*/
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import { fetchWithTimeout, readBytesCapped } from "./fetch.ts";
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/**
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* Returned to `GET /api/proxy-image` by {@link fetchProxiedImage}, which sends
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* it back under `contentType`.
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*/
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export interface ProxiedImage {
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bytes: Uint8Array;
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/** One of the raster types, without parameters. */
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contentType: string;
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}
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const PROXYABLE_IMAGE_TYPES = new Set([
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"image/jpeg",
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"image/png",
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"image/gif",
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"image/webp",
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"image/avif",
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"image/bmp",
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"image/x-icon",
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"image/vnd.microsoft.icon",
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]);
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const IMAGE_CACHE_TTL_MS = 24 * 60 * 60 * 1000;
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const IMAGE_CACHE_MAX_BYTES = 32 * 1024 * 1024;
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/**
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* Proxied images, by URL, since every viewer of a feed asks for the same
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* thumbnails. The least recently used go first, and the Map's order is that
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* of use.
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*/
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const imageCache = new Map<
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string,
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{ bytes: Uint8Array; contentType: string; at: number }
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>();
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let imageCacheBytes = 0;
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function readImageCache(
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url: string,
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): { bytes: Uint8Array; contentType: string } | undefined {
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const hit = imageCache.get(url);
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if (!hit) return undefined;
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imageCache.delete(url);
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if (Date.now() - hit.at > IMAGE_CACHE_TTL_MS) {
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imageCacheBytes -= hit.bytes.byteLength;
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return undefined;
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}
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imageCache.set(url, hit); // Moves it to the end: most recently used.
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return hit;
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}
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function writeImageCache(
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url: string,
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bytes: Uint8Array,
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contentType: string,
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): void {
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const old = imageCache.get(url);
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if (old) {
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imageCache.delete(url);
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imageCacheBytes -= old.bytes.byteLength;
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}
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while (
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imageCacheBytes + bytes.byteLength > IMAGE_CACHE_MAX_BYTES &&
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imageCache.size > 0
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) {
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const [oldestUrl, oldest] = imageCache.entries().next().value!;
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imageCache.delete(oldestUrl);
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imageCacheBytes -= oldest.bytes.byteLength;
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}
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imageCache.set(url, { bytes, contentType, at: Date.now() });
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imageCacheBytes += bytes.byteLength;
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}
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/** Empties the cache, for the tests' reset between cases. */
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export function clearImageCache(): void {
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imageCache.clear();
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imageCacheBytes = 0;
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}
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/**
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* Returns the image at `url`, from the cache or else from its host; null when
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* the host answers with an error, or with anything but a raster image of 5 MB
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* at most. The route
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* checks `url` with `isValidHttpUrl` first.
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*
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* @throws {Error} When the host can't be reached, as
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* {@link fetchWithTimeout} reports it.
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*/
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export async function fetchProxiedImage(
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url: string,
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): Promise<ProxiedImage | null> {
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const cached = readImageCache(url);
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if (cached) return cached;
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const res = await fetchWithTimeout(url, 8000);
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if (!res.ok) {
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await res.body?.cancel();
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return null;
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}
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// Raster formats only: the bytes go out under this site's origin, where an
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// SVG, which can carry script, would run if opened directly.
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const contentType = (res.headers.get("content-type") ?? "")
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.split(";")[0].trim().toLowerCase();
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if (!PROXYABLE_IMAGE_TYPES.has(contentType)) {
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await res.body?.cancel();
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return null;
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}
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const MAX_SIZE = 5 * 1024 * 1024;
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const contentLength = Number(res.headers.get("content-length") ?? "0");
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if (contentLength > MAX_SIZE) {
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await res.body?.cancel();
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return null;
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}
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// Without a Content-Length, the cap is found by reading one byte past it.
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const bytes = await readBytesCapped(res, MAX_SIZE + 1);
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if (bytes.length > MAX_SIZE) return null;
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writeImageCache(url, bytes, contentType);
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return { bytes, contentType };
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}
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