92 lines
2.9 KiB
TypeScript
92 lines
2.9 KiB
TypeScript
/**
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* Fetches link previews for the create form, and proxies the remote images
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* that the frontend's thumbnails can't load directly.
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*
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* - `GET /api/preview?url=` — signed in. Answers the preview of a link, and
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* whether its page could be reached.
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* - `GET /api/proxy-image?url=` — public. Serves a remote raster image through
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* this site; 400 when it isn't one, 502 when its host can't be reached.
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*
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* @module
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*/
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import { Router } from "@oak/oak";
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import { isValidHttpUrl } from "../remote/fetch.ts";
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import { fetchProxiedImage } from "../remote/image-proxy.ts";
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import { tryFetchRichContent } from "../services/rich-content-service.ts";
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import {
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APIErrorCode,
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type APIFailure,
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type APIResponse,
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} from "../../shared/api.ts";
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import type { LinkPreview } from "../../shared/dump.ts";
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import { authMiddleware } from "../middleware/auth.ts";
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/**
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* Mounted by `api/main.ts` behind the error, Open Graph and CORS middleware.
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* An `APIException` thrown by a handler becomes the JSON error response there.
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*/
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const previewRouter: Router = new Router();
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// Signed-in only: an open preview would let anyone make the server fetch pages.
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previewRouter.get("/api/preview", authMiddleware, async (ctx) => {
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const url = ctx.request.url.searchParams.get("url") ?? "";
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if (!isValidHttpUrl(url)) {
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const responseBody: APIFailure = {
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success: false,
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error: { code: APIErrorCode.VALIDATION_ERROR, message: "Invalid URL" },
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};
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ctx.response.status = 400;
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ctx.response.body = responseBody;
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return;
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}
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const { ok, content } = await tryFetchRichContent(url);
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const responseBody: APIResponse<LinkPreview> = {
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success: true,
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data: { reached: ok, richContent: content ?? null },
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};
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ctx.response.body = responseBody;
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});
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/**
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* Answers with a proxied image. It is sent from this site's origin, so it is
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* sandboxed in case a browser opens it as a document.
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*/
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function sendImage(
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ctx: { response: { headers: Headers; body?: unknown } },
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bytes: Uint8Array,
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contentType: string,
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): void {
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ctx.response.headers.set("Content-Type", contentType);
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ctx.response.headers.set("X-Content-Type-Options", "nosniff");
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ctx.response.headers.set(
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"Content-Security-Policy",
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"sandbox; default-src 'none'",
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);
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ctx.response.headers.set("Cache-Control", "public, max-age=86400");
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ctx.response.body = bytes;
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}
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// The frontend sends a thumbnail here when it is plain HTTP, which an HTTPS
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// page won't load, or when its host's hotlink protection refused the browser.
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previewRouter.get("/api/proxy-image", async (ctx) => {
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const url = ctx.request.url.searchParams.get("url") ?? "";
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if (!isValidHttpUrl(url)) {
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ctx.response.status = 400;
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return;
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}
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try {
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const image = await fetchProxiedImage(url);
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if (!image) {
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ctx.response.status = 400;
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return;
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}
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sendImage(ctx, image.bytes, image.contentType);
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} catch {
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ctx.response.status = 502;
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}
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});
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export default previewRouter;
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