Add support for ETag-based caching

[developit]

When providing an ETag header on responses, the client automatically sends that header value on subsequent requests for the matching resource as an If-None-Match request header. If the ETag value received in If-None-Match is the same as the ETag computed by the disk crawl, a 304 "Not Modified" status can be returned along with an empty body to indicate that the requestor's cached value should be used.

---

I'm currently using the following workaround to implement this manually:

server.use((req, res, next) => {
	// `req` is not passed to setHeaders(), so we obtain that info here
	res._requestHeaders = req.headers;
	next();
});

server.use(
	sirv('public', {
		etag: true,
		setHeaders(res, path, stats) {
			const etag = res._requestHeaders['if-none-match'];
			const computedEtag = `W/"${stats.size}-${stats.mtime.getTime()}"`;
			if (etag && etag === computedEtag) {
				res.writeHead(304);
				res.end();
				// hack: disable sirv's normal response & piping:
				res.writeHead = res.write = res.end = () => {};
			}
		}
	})
);

[lukeed]

Awesome, thanks! Can you add this into next branch though? I'm gunning to release 1.0 this week

[developit]

@lukeed fixed!

[lukeed]

Thank you 🙏 Little embarrassed I added ETag w/o its counterpart haha

[lukeed]

Available as:

• sirv-cli@1.0.0-next.4
• sirv@1.0.0-next.4