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81 lines
3.5 KiB
81 lines
3.5 KiB
class GifHelper {
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/// Parse a known GIF format, which can be any of:
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/// g:GIFID
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/// https://media.giphy.com/media/GIFID/giphy.gif
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/// https://giphy.com/gifs/Optional-title-with-dashes-GIFID
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///
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/// GIFID is a Giphy GIF ID. The https:// is optional (and
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/// can also be http://). The giphy.com/gifs form can also
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/// include a trailing slash.
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///
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/// Returns null if text is not a valid GIF format
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static String? parseGif(String text) {
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// A reply prepends a leading `@[Name] ` mention; ignore it so a reply-gif
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// still resolves to the gif rather than plain text. Only a reply mention is
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// stripped — arbitrary text before a gif is left as text. (#232)
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final trimmed = text.trim().replaceFirst(RegExp(r'^@\[[^\]]+\]\s+'), '');
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final match = RegExp(r'^g:([A-Za-z0-9_-]+)$').firstMatch(trimmed);
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if (match != null) {
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return match.group(1);
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}
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final directUrlMatch = RegExp(
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r'^(?:https?:\/\/)?media\.giphy\.com\/media\/([A-Za-z0-9_-]+)\/giphy\.gif$',
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).firstMatch(trimmed);
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if (directUrlMatch != null) {
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return directUrlMatch.group(1);
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}
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// Giphy understands page URLs with just the ID, or any string and a
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// dash before the ID, and redirects to a page with a dash-separated
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// title, a dash, and the ID. IDs in this form *probably* can't
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// contain dashes.
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final pageMatch = RegExp(
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r'^(?:https?:\/\/)?giphy\.com\/gifs\/(?:[^/?]*-)?([A-Za-z0-9_]+)\/?$',
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).firstMatch(trimmed);
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if (pageMatch != null) {
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return pageMatch.group(1);
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}
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// The CDN form people actually paste out of a browser. (#283)
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final cdnMatch = RegExp(
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r'^(?:https?:\/\/)?i\.giphy\.com\/([A-Za-z0-9_-]+)\.(?:gif|webp)$',
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).firstMatch(trimmed);
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return cdnMatch?.group(1);
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}
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/// Encode a GIF as a Giphy page URL, a format parseGif() also parses.
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///
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/// A real URL rather than the lineage-only `g:<id>` token: recipients on
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/// stock (or any non-lineage) MeshCore client can open it, where `g:<id>`
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/// is opaque text to them. parseGif already matches this form, so Offband
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/// keeps rendering inline and legacy `g:<id>` payloads still decode. (#282)
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static String encodeGif(String gifId) {
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return 'https://giphy.com/gifs/$gifId';
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}
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/// Tenor's own CDN, the only Tenor form that is directly renderable.
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///
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/// A `tenor.com/view/<slug>-<id>` page URL is deliberately NOT matched: the
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/// modern CDN path uses an opaque hash that cannot be derived from the page
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/// id, so resolving one needs the Tenor API. Such a link stays plain text
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/// rather than silently rendering the wrong image. (#283)
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static final RegExp _tenorMedia = RegExp(
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r'^(?:https?:\/\/)?(?:media|c)\.tenor\.com\/[A-Za-z0-9_\-\/]+\.(?:gif|webp)$',
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);
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/// The URL that renders [text], or null if it is not a GIF we will display.
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///
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/// Rendering is restricted to an allowlist of curated GIF platforms (Giphy
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/// and Tenor). Anything off-list returns null and stays a plain tap-to-open
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/// link: auto-fetching an arbitrary URL leaks the viewer's IP and enables
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/// tracking-pixel abuse, and inline-rendering unmoderated hosts is a malware
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/// and inappropriate-content vector. Widening the allowlist is a deliberate
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/// decision, not a convenience. (#283)
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static String? resolveGifUrl(String text) {
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final gifId = parseGif(text);
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if (gifId != null) {
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return 'https://media.giphy.com/media/$gifId/giphy.gif';
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}
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final trimmed = text.trim().replaceFirst(RegExp(r'^@\[[^\]]+\]\s+'), '');
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return _tenorMedia.hasMatch(trimmed) ? trimmed : null;
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}
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}
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