AJAX - The Complete Reference

596 Part IV: Appendixes

Custom Request Headers

It is possible to set your own custom HTTP request headers. Custom headers should use a

prefix X- to indicate they are extensions to the protocol. Beyond that, the header name and

allowed values are up to the imagination of the developer.

X-Debug: True

X-JavaScript-Version-Requested: 1.7

X-Cylon-Model: 6

Request Header Description Examples

Range Indicates a request for a particular

range of a file, such as a certain

number of bytes. The examples show

a request for the last 500 bytes of

a file as well as one requesting two

ranges of bytes. This type of request

will be found with content of type

multipart/byteranges.

Range: bytes=-500

Range: bytes=1036930-

1043528,1036928-1036929

Referer Indicates the URL of the document

from which the request originates (in

other words, the linking document).

This value might be empty if the user

has entered the URL directly rather

than by following a link. Some users

concerned with privacy may also

clear out their Referer headers, so

do not rely on its presence. Note the

misspelling. It is properly written in

the misspelled form.

Referer: http://ajaxref.com/

chapters/index.html

TE Indicates what transfer encodings

the client is willing to accept and

whether or not it will accept trailer

fields in chunked transfers. The

header value may contain the

keyword trailers and/or a list of

accepted encodings. As the header

overlaps with Accept-Encoding,

it appears not to be used in the

later form often.

TE: trailers

TE: gzip

User-Agent Indicates the type of browser

making the request. Very useful for

browser detection, but developers

should not trust it completely as it

is often falsified by clients for both

legitimate and nefarious reasons.

User-Agent: Mozilla/5.0

(Windows; U; Windows NT

5.1; en-US; rv:1.8.1.3)

Gecko/20070309

Firefox/2.0.0.3

TABLE B-5 HTTP 1.1 Request Headers (continued)