111 lines
3.4 KiB
TypeScript
111 lines
3.4 KiB
TypeScript
/**
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* The canonical form of a URL, used *only* to recognise that two links point at the
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* same thing — the duplicate check the create form runs while it fetches a
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* preview. It is a lookup key, never something we display or fetch: `dumps.url`
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* keeps the exact string the poster submitted.
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*
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* Because it is only ever compared against other canonical forms, it may be
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* lossy in ways a real URL never could be — it forces `https`, drops `www.`,
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* and throws away share/tracking parameters and timestamps, so
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* `http://www.example.com/a/?utm_source=x` and `https://example.com/a` collapse
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* to one key.
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*
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* Stored in `dumps.url_canonical`. Migration 0013 carries a frozen copy of this
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* logic to backfill existing rows; changing the rules here therefore needs a
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* new backfill migration, or old rows keep keys computed under the old rules.
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*
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* @module
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*/
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const TRACKING_PARAMS = new Set([
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"fbclid",
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"gclid",
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"dclid",
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"msclkid",
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"twclid",
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"yclid",
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"mc_cid",
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"mc_eid",
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"igshid",
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"igsh",
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"si",
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"spm",
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"ref_src",
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"ref_url",
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"_ga",
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"_gl",
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"__twitter_impression",
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]);
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function isTrackingParam(key: string): boolean {
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const k = key.toLowerCase();
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return k.startsWith("utm_") || TRACKING_PARAMS.has(k);
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}
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/** YouTube's hosts, already stripped of a leading "www.". */
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const YOUTUBE_HOSTS = new Set([
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"youtube.com",
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"m.youtube.com",
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"music.youtube.com",
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"youtube-nocookie.com",
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]);
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/**
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* Returns the video a YouTube URL points at, in any of the shapes people paste
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* (`youtu.be/ID`, `/watch?v=ID`, `/embed/ID`, `/shorts/ID`, `/live/ID`).
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* Timestamps are deliberately ignored: the same video linked at 2:30 is still
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* the same video for duplicate purposes.
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*/
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function youtubeVideoId(
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host: string,
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pathname: string,
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params: URLSearchParams,
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): string | null {
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if (host === "youtu.be") return pathname.split("/")[1] || null;
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if (!YOUTUBE_HOSTS.has(host)) return null;
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if (pathname === "/watch") return params.get("v");
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if (/^\/(embed|shorts|live)\//.test(pathname)) {
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return pathname.split("/")[2] || null;
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}
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return null;
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}
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/**
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* Returns the canonical form of `raw` (see the module doc), or null when it
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* isn't an http(s) URL.
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*/
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export function canonicalizeUrl(raw: string): string | null {
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let u: URL;
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try {
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u = new URL(raw);
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} catch {
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return null;
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}
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if (u.protocol !== "http:" && u.protocol !== "https:") return null;
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const host = u.hostname.toLowerCase().replace(/^www\./, "");
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if (!host) return null;
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const videoId = youtubeVideoId(host, u.pathname, u.searchParams);
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if (videoId) return `https://youtube.com/watch?v=${videoId}`;
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const listId = YOUTUBE_HOSTS.has(host) && u.pathname === "/playlist"
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? u.searchParams.get("list")
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: null;
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if (listId) return `https://youtube.com/playlist?list=${listId}`;
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// A single trailing slash is never meaningful; "/" itself becomes "".
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const path = u.pathname.replace(/\/+$/, "");
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const params = [...u.searchParams.entries()]
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.filter(([key]) => !isTrackingParam(key))
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.sort(([a, av], [b, bv]) => a.localeCompare(b) || av.localeCompare(bv));
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const query = new URLSearchParams(params).toString();
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// A bare "#section" anchor points into the same page, so it is dropped —
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// but "#/route" and "#!/route" address distinct pages of a hash-routed app.
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const hash = /^#!?\//.test(u.hash) ? u.hash : "";
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return `https://${host}${path}${query ? `?${query}` : ""}${hash}`;
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}
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