E-Tag in http header

Question

When i gave the HEAD request for a file i got ETAG header as follows:

ETag: "49a81-3f-4c049ee89a31b"

In this the first part is Inode what are the other fields

Could anyone tell me. Thanks in advance

Answer 1

ETag is as far as I know just any string.

If the one your browser has matches the one on the server, you get a 304 message, not changed and if not you get an 200 along with the new version.

Different implementations might add Inode or dates or anything, really.

I personally use a version number to force new js script versions to be loaded when we update our application.

Other posts on ETag:
HTTP: Generating ETag Header
Syntax for ETag?

Answer 2

From wikipedia i got this information:

An ETag is an opaque identifier assigned by a web server to a specific version of a resource found at a URL. If the resource content at that URL ever changes, a new and different ETag is assigned. Used in this manner ETags are similar to fingerprints, and they can be quickly compared to determine if two versions of a resource are the same or not.

Comparing ETags only makes sense with respect to one URL—ETags for resources obtained from different URLs may or may not be equal. So no meaning can be inferred from their comparison.

To my knowledge etag is used to check the files has been modified since download.

In your Etag the parts may represent: inode-file_size-last_modified_time may be used. I am not sure about it.

And moreover the post by david has more information. Follow that too. Those information are really good and useful.