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