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HTTP General Headers
(Page 3 of 3)
Upgrade
Allows a client device to specify
what additional protocols it supports. If the server also supports one
of the protocols the client listed, the server may agree to upgrade
the connection to the alternative protocol. It indicates the protocol
to which it is upgrading by including an Upgrade header in a
101 (Switching Protocols) response to the client.
This is a hop-by-hop header.
Via
Included by intermediary devices
to indicate to the recipient what gateways, proxies and/or tunnels were
used in conveying a request or response. This header allows easy tracing
of the path a message took over a potentially complex chain of devices
between a client and server.
Warning
Used when needed to provide additional
information about the status of a message. Many of the defined warning
header types are related to caching. More than one Warning header
may appear in a message, and each typically includes a three-digit numeric
code as well as a plain text messagethe same basic format used
in HTTP
response status codes.
Table 277
briefly lists the warnings defined in RFC 2616.
Table 277: HTTP Warning Header Codes
Warning
Code
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Warning
Text
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Description
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110
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Response is
stale
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Must be included when a response
provided by a cache is stale (that is, has passed the expiration time
set for it.)
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111
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Revalidation
failed
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A cache attempted
to revalidate a cached entry but was unsuccessful, so it returned its
(stale) cached entry.
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112
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Disconnected
operation
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The cache is disconnected from
the rest of the network.
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113
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Heuristic
expiration
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Included if
the cache chose a freshness lifetime of more than 24 hours, and the
age of the response is also greater than 24 hours.
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199
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Miscellaneous
warning
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Catch-all code for other, non-specific
warnings.
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214
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Transformation
applied
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Warns the recipient
that an intermediate cache or proxy applied a transformation of some
type to change the content
coding or media
type of the message or message body.
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299
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Miscellaneous
persistent warning
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Similar to code 199 but indicates
a persistent warning.
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Key Concept: HTTP general headers can appear in either an HTTP Request or HTTP Response message. They are used to communicate information about the message itself, as opposed to its contents. General headers are used for functions such as specifying the date and time of a message, controlling how the message is cached, and indicating its transfer encoding method. |
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Version 3.0 - Version Date: September 20, 2005
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