AJAX - The Complete Reference

PART IV

Appendix B: HTTP 1.1 Reference 603

Response Header Description Example

Accept-Ranges Allows the server to indicate its acceptance

of range requests for a resource. Usually

the value is bytes and is commonly seen

in progressive PDF file fetches. A value of

none is also allowed.

Accept-Ranges: bytes

Age Shows the sender's estimate of the amount

of time since the response was generated

at the origin server. Age values are

nonnegative decimal integers, representing

time in seconds.

Age: 10

ETag Specifies a unique value called an entity tag

for the requested resource. This improves

caching and is used with If-Match and

If-None-Match request headers.

ETag: 4135cda4

Keep-Alive While not part of the HTTP 1.1 specification,

this commonly seen header is used to

maintain persistent connections with some

browsers and proxies.

Keep-Alive: timeout=15,

max=100

Location Specifies the location to redirect the client

to in the case of 3XX responses. Must

contain an absolute URL value.

Location:

http://ajaxref.com/

browserupgrade.php

Proxy-

Authenticate

Included with a 407 (Proxy Authentication

Required) response. The value of the field

consists of a challenge that indicates the

authentication scheme and parameters

applicable to the proxy for the request.

Proxy-Authenticate:

Basic Realm=CIC

Public Not defined in the HTTP 1.1 specification,

this header is returned after an OPTIONS

method and lists the set of methods

supported by the server. The purpose of

this header is strictly to inform the browser

of the capabilities of the server when new

or unusual methods are encountered.

Public: OPTIONS, MGET,

MHEAD, GET, HEAD

Retry-After Can be used in conjunction with a 503

(Service Unavailable) response to indicate

how long the service is expected to be

unavailable to the requesting client. The

value of this field can be either an HTTP-date

or an integer number of seconds after which

to retry.

Retry-after: Fri, 31 Dec

1999 23:59:59 GMT

Retry-after: 60

Server Contains information about the Web

software used. Some servers may remove

or mask this header to avoid information

leakage about their site implementation.

Server: Apache/1.3.12

(Unix)

Server: Servermasked!

TABLE B-8 Common HTTP 1.1 Server Response Headers