As long as it changes whenever the resource representation changes, how you produce it is completely up to you. You should try to produce it in a way that additionally: doesn’t require you to re-compute it on each conditional GET, and doesn’t change if the resource content hasn’t changed Using hashes of content can cause … Read more
Try ETag: “4ae413bd”. The value of an ETag must follow the ABNF form: entity-tag = [ weak ] opaque-tag weak = “W/” opaque-tag = quoted-string quoted-string = ( <“> *(qdtext | quoted-pair ) <“> ) qdtext = <any TEXT except <“>> quoted-pair = “\” CHAR CHAR = <any US-ASCII character (octets 0 – 127)> TEXT … Read more
Upgrade your Nginx. Syntax: etag on | off; Default: etag on; Context: http, server, location This directive appeared in version 1.3.3. Enables or disables automatic generation of the “ETag” response header field for static resources. Source: http://nginx.org/en/docs/http/ngx_http_core_module.html#etag
Expires and Cache-Control are “strong caching headers” Last-Modified and ETag are “weak caching headers” First the browser checks Expires/Cache-Control to determine whether or not to make a request to the servers. If it has to make a request, it will send Last-Modified/ETag in the HTTP request. If the Etag value of the document matches that, … Read more
ETag is similar to the Last-Modified header. It’s a mechanism to determine change by the client. An ETag needs to be a unique value representing the state and specific format of a resource (a resource could have multiple formats that each need their own ETag). Not unique across the entire domain of resources, simply within … Read more
RFC7232 updates RFC2616 to say: The server generating a 304 response MUST generate any of the following header fields that would have been sent in a 200 (OK) response to the same request: Cache-Control, Content-Location, Date, ETag, Expires, and Vary.
Firstly, the relevant HTTP spec is RFC 7234. If you look at the spec you will observe two things: The spec never requires, under any circumstances, that a cache serves a cached version of content without revalidating. There are plenty of places where the spec notes that a cache MUST NOT use cached content to … Read more
@Elijah Glover’s answer is part of the answer, but not really complete. This will set the ETag, but you’re not getting the benefits of ETags without checking it on the server side. You do that with: var requestedETag = Request.Headers[“If-None-Match”]; if (requestedETag == eTagOfContentToBeReturned) return new HttpStatusCodeResult(HttpStatusCode.NotModified); Also, another tip is that you need to … Read more
Let me explain it in 2021, with updated information and links to the code. It’s a relatively straightforward and simple (no rocket science) concept, but, at the same, a very tricky thing that as a developer you should really know before it comes to bite you! What is Etag? So, Etag (per Wikipedia/Etag), is a … Read more
According to RFC 2616 – section 13.3.4, an HTTP 1.1 Client MUST use the ETag in any cache-conditional requests, and if both an ETag and Last Modified are present, it SHOULD use both. The ETag header is considered a strong validator (see section 13.3.3), unless explicitly declared weak by the server, whereas the Last Modified … Read more