Understanding etags

I have two sets of cached resources, some in R2 some from an API we have.

I want to use the etag to avoid fetching the body of each if it hasn't changed. I see an etag header on the R2 buckets but not in responses from the (cached) API response (only a Last-Modified).

Is R2 generating the etag and sending it along and I need to do the same on my API, or is there a way to get CF to generate an etag based on the cached proxied API resource?

Viktor•5/13/25, 6:58 PM

You need to send etag headers yourself.

Is your API hosted on workers/pages?

        const object = await env.MY_BUCKET.get(key);

        if (object === null) {
          return new Response("Object Not Found", { status: 404 });
        }

        const headers = new Headers();
        object.writeHttpMetadata(headers);
        headers.set("etag", object.httpEtag);

        return new Response(object.body, {
          headers,
        });

        const object = await env.MY_BUCKET.get(key);

        if (object === null) {
          return new Response("Object Not Found", { status: 404 });
        }

        const headers = new Headers();
        object.writeHttpMetadata(headers);
        headers.set("etag", object.httpEtag);

        return new Response(object.body, {
          headers,
        });

See: https://developers.cloudflare.com/r2/api/workers/workers-api-usage/

Cloudflare Docs

Use R2 from Workers

C3 (create-cloudflare-cli) is a command-line tool designed to help you set up and deploy Workers & Pages applications to Cloudflare as fast as possible.

MattOP•5/13/25, 7:00 PM

It's not it's just a Fastify rest api we host and proxy thru CF. I guess my naïve question is why CF can't generate an etag based on the cached entity. Totally don't mind sending it mostly curious

MMatt It's not it's just a Fastify rest api we host and proxy thru CF. I guess my naïv...

Viktor•5/13/25, 7:05 PM

Cloudflare needs to proxy the request to your origin API anyways, as it is not able to handle the etag by itself.
So I guess the benefit wasn‘t big enough generating an own etag and storing that.

Viktor•5/13/25, 7:06 PM

Also generating them on the origin server is way more straight forward

MattOP•5/13/25, 7:06 PM

makes sense

const object = await env.MY_BUCKET.get(key); if (object === null) { return new Response("Object Not Found", { status: 404 }); } const headers = new Headers(); object.writeHttpMetadata(headers); headers.set("etag", object.httpEtag); return new Response(object.body, { headers, });

Understanding etags

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