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 is ETag processing?

An entity tag (ETag) is an HTTP header used for Web cache validation and conditional request from browsers to resources. The value of an ETag is an identifier that represents a specific version of the resource. Additionally, ETags help prevents simultaneous updates of a resource from overwriting each other.

How do ETag headers work?

The ETag (or Entity Tag) works in a similar way to the Last-Modified header except its value is a digest of the resources contents (for instance, an MD5 hash). This allows the server to identify if the cached contents of the resource are different to the most recent version.

How are ETags stored in the REST API?

First, the Client makes a REST API call – the Response includes the ETag header that will be stored for further use: For the next request, the Client will include the If-None-Match request header with the ETag value from the previous step.

What is the purpose of an ETag in http?

Etag, also known as entity tag is an HTTP response header returned by an HTTP/1.1 compliant web server used to determine a change in content at a given URL. On a high level, there are two main uses of for Etags:

How to compare ETag values in REST API call-code SharePoint?

When you get (REST-API GET) the resource, you can store the Etag value of the resource in a hidden field. When you update/delete (REST-API POST) the data back, you can compare the stored Etag value with the Etag value of the resource. If both values match, then you can go ahead and perform your action. How to compare Etag values?

When do you change the ETag of a request?

For example, if you send a request to get a specific customer: Then the ETag (if used) is included in the header in the response: Each time the resource is updated on the server, the ETag header will be changed to reflect the content of the new version of the resource.