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[READ-ONLY] Mirror of https://github.com/flo-bit/atmo-watch. atmo.watch
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2.8 kB · 85 lines
TypeScript
at main
1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586import { getCloudflareCache } from '$lib/cache.server';
const OG_IMAGE_TTL = 24 * 60 * 60;// Bump this version when changing the image template or renderer.const CACHE_URL_BASE = 'https://atmo.watch/__og-image-cache/v1/';
type BufferedImage = { body: ArrayBuffer; status: number; headers: [string, string][];};
// Only retain in-flight images in memory, not a potentially large PNG collection.// Coalescing is local to this isolate; Cache API entries are local to a data center.const pendingImages = new Map<string, Promise<BufferedImage>>();
function toResponse(image: BufferedImage) { return new Response(image.body, { status: image.status, headers: image.headers });}
async function bufferResponse(response: Response): Promise<BufferedImage> { return { body: await response.arrayBuffer(), status: response.status, headers: [...response.headers.entries()] };}
function isCacheableImage(response: Response) { return ( response.status === 200 && response.headers.get('content-type')?.split(';')[0].trim().toLowerCase() === 'image/png' && !response.headers.has('set-cookie') && !/(?:private|no-store|no-cache)/i.test(response.headers.get('cache-control') ?? '') );}
async function loadImage(key: string, render: () => Promise<Response>): Promise<BufferedImage> { const request = new Request(`${CACHE_URL_BASE}${encodeURIComponent(key)}`); const cache = getCloudflareCache();
try { const cached = await cache?.match(request); if (cached && isCacheableImage(cached)) return await bufferResponse(cached); } catch { // Cache failures must not prevent generating a public preview image. }
const response = await render(); const cacheable = isCacheableImage(response); const image = await bufferResponse(response); if (!cacheable) return image;
const headers = new Headers(image.headers); // Cache API does not implement stale-while-revalidate. Use an explicit TTL. headers.set('Cache-Control', `public, max-age=${OG_IMAGE_TTL}`); image.headers = [...headers.entries()];
try { // Await storage so a following request cannot miss between render and put. await cache?.put(request, toResponse(image)); } catch { // Still return the rendered image if Cache API is unavailable or full. }
return image;}
/** Cache only public PNGs. Each caller receives a fresh, independently readable body. */export async function cacheOgImage( key: string, render: () => Promise<Response>): Promise<Response> { let pending = pendingImages.get(key); if (!pending) { pending = loadImage(key, render).finally(() => { pendingImages.delete(key); }); pendingImages.set(key, pending); }
// Do not share a streaming Response across requests: its I/O belongs to the // request that created it in Workers. Only share the fully buffered image. return toResponse(await pending);}