Users' questions

How is ETag calculated?

How is ETag calculated?

An ETag (entity tag) is an HTTP response header returned by an HTTP/1.1 compliant web server used to determine change in content at a given URL. We can use ETags for two things – caching and conditional requests. The ETag value can be thought of as a hash computed out of the bytes of the Response body.

What is ETag in a web service?

The ETag or entity tag is part of HTTP, the protocol for the World Wide Web. It is one of several mechanisms that HTTP provides for Web cache validation, which allows a client to make conditional requests. An ETag is an opaque identifier assigned by a Web server to a specific version of a resource found at a URL.

What does ETag stand for?

An entity tag (ETag) is an HTTP header used for Web cache validation and conditional requests from browsers for resources. Etags use persistent identification elements (PIE) that have been tagged to the user’s browser.

Can a MD5 be used as an object ETag?

In the past, MD5s were used as object ETags, but users should avoid assuming this since some objects use opaque ETag values that make no guarantees outside of changing when the object changes. Server-side upload validation can be performed by supplying locally computed hashes via the x-goog-hash request header.

Is the entity tag a hash or MD5 digest?

The entity tag is a hash of the object. The ETag reflects changes only to the contents of an object, not its metadata. The ETag may or may not be an MD5 digest of the object data. Whether or not it is depends on how the object was created and how it is encrypted as described below:

Why do we need an ETag for an HTTP response?

ETag. The ETag HTTP response header is an identifier for a specific version of a resource. It lets caches be more efficient and save bandwidth, as a web server does not need to resend a full response if the content has not changed. Additionally, etags help prevent simultaneous updates of a resource from overwriting each other

Which is an example of an ETag in MDN?

For example, MDN uses a hexadecimal hash of the wiki article content. With the help of the ETag and the If-Match headers, you can detect mid-air edit collisions. For example, when editing MDN, the current wiki content is hashed and put into an Etag in the response: