HTTP Pocket Reference

HEAD: Retrieve Header Information

The HEAD method is functionally like GET, except that the server replies with a response line and headers, but no entity-body. The headers returned by the server with the HEAD method should be exactly the same as the headers returned with a GET request. This method is often used by web clients to verify the document’s existence or properties (like Content-length or Content-type), but the client has no intention of retrieving the document in the transaction. Many applications exist for the HEAD method, which make it possible to retrieve:

• Modification time of a document for caching purposes

• Size of the document, to do page layout, estimate arrival time, or skip the document and retrieve a smaller version of the document

• Type of the document, to allow the client to examine only documents of a certain type

• Type of server, to allow customized server queries

It is important to note that most of the header information provided by a server is optional, and may not be given by all servers.

For example:

GET / HTTP/1.1
Accept: image/gif, image/x-xbitmap, 
   image/jpeg, image/pjpeg, */*
Accept-Language: en-us
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE
   5.01; Windows NT)
Host: hypothetical.ora.com
Connection: Keep-Alive

The server responds with:

HTTP/1.1 200 OK Date: Mon, 06 Dec 1999 20:54:26 GMT Server: Apache/1.3.6 (Unix) Last-Modified: Fri, 04 Oct 1996 14:06:11 GMT ETag: "2f5cd-964-381e1bd6" Accept-Ranges: bytes Content-length: 327 Connection: ...