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Authorization = "Authorization" ":" credentials
HTTP access authentication is described in section 11. If a request
is authenticated and a realm specified, the same credentials SHOULD
be valid for all other requests within this realm.
When a shared cache (see section 13.7) receives a request containing
an Authorization field, it MUST NOT return the corresponding response
as a reply to any other request, unless one of the following specific
exceptions holds:
1. If the response includes the "proxy-revalidate" Cache-Control
directive, the cache MAY use that response in replying to a
subsequent request, but a proxy cache MUST first revalidate it with
the origin server, using the request-headers from the new request
to allow the origin server to authenticate the new request.
2. If the response includes the "must-revalidate" Cache-Control
directive, the cache MAY use that response in replying to a
subsequent request, but all caches MUST first revalidate it with
the origin server, using the request-headers from the new request
to allow the origin server to authenticate the new request.
3. If the response includes the "public" Cache-Control directive, it
may be returned in reply to any subsequent request.
14.9 Cache-Control
The Cache-Control general-header field is used to specify directives
that MUST be obeyed by all caching mechanisms along the
request/response chain. The directives specify behavior intended to
prevent caches from adversely interfering with the request or
response. These directives typically override the default caching
algorithms. Cache directives are unidirectional in that the presence
of a directive in a request does not imply that the same directive
should be given in the response.
Note that HTTP/1.0 caches may not implement Cache-Control and may
only implement Pragma: no-cache (see section 14.32).
Cache directives must be passed through by a proxy or gateway
application, regardless of their significance to that application,
since the directives may be applicable to all recipients along the
request/response chain. It is not possible to specify a cache-
directive for a specific cache.
Cache-Control = "Cache-Control" ":" 1#cache-directive
cache-directive = cache-request-directive
| cache-response-directive
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cache-request-directive =
"no-cache" [ "=" <"> 1#field-name <"> ]
| "no-store"
| "max-age" "=" delta-seconds
| "max-stale" [ "=" delta-seconds ]
| "min-fresh" "=" delta-seconds
| "only-if-cached"
| cache-extension
cache-response-directive =
"public"
| "private" [ "=" <"> 1#field-name <"> ]
| "no-cache" [ "=" <"> 1#field-name <"> ]
| "no-store"
| "no-transform"
| "must-revalidate"
| "proxy-revalidate"
| "max-age" "=" delta-seconds
| cache-extension
cache-extension = token [ "=" ( token | quoted-string ) ]
When a directive appears without any 1#field-name parameter, the
directive applies to the entire request or response. When such a
directive appears with a 1#field-name parameter, it applies only to
the named field or fields, and not to the rest of the request or
response. This mechanism supports extensibility; implementations of
future versions of the HTTP protocol may apply these directives to
header fields not defined in HTTP/1.1.
The cache-control directives can be broken down into these general
categories:
o Restrictions on what is cachable; these may only be imposed by the
origin server.
o Restrictions on what may be stored by a cache; these may be imposed
by either the origin server or the user agent.
o Modifications of the basic expiration mechanism; these may be
imposed by either the origin server or the user agent.
o Controls over cache revalidation and reload; these may only be
imposed by a user agent.
o Control over transformation of entities.
o Extensions to the caching system.
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14.9.1 What is Cachable
By default, a response is cachable if the requirements of the request
method, request header fields, and the response status indicate that
it is cachable. Section 13.4 summarizes these defaults for
cachability. The following Cache-Control response directives allow an
origin server to override the default cachability of a response:
public
Indicates that the response is cachable by any cache, even if it
would normally be non-cachable or cachable only within a non-shared
cache. (See also Authorization, section 14.8, for additional
details.)
private
Indicates that all or part of the response message is intended for a
single user and MUST NOT be cached by a shared cache. This allows an
origin server to state that the specified parts of the response are
intended for only one user and are not a valid response for requests
by other users. A private (non-shared) cache may cache the response.
Note: This usage of the word private only controls where the
response may be cached, and cannot ensure the privacy of the
message content.
no-cache
Indicates that all or part of the response message MUST NOT be cached
anywhere. This allows an origin server to prevent caching even by
caches that have been configured to return stale responses to client
requests.
Note: Most HTTP/1.0 caches will not recognize or obey this
directive.
14.9.2 What May be Stored by Caches
The purpose of the no-store directive is to prevent the inadvertent
release or retention of sensitive information (for example, on backup
tapes). The no-store directive applies to the entire message, and may
be sent either in a response or in a request. If sent in a request, a
cache MUST NOT store any part of either this request or any response
to it. If sent in a response, a cache MUST NOT store any part of
either this response or the request that elicited it. This directive
applies to both non-shared and shared caches. "MUST NOT store" in
this context means that the cache MUST NOT intentionally store the
information in non-volatile storage, and MUST make a best-effort
attempt to remove the information from volatile storage as promptly
as possible after forwarding it.
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Even when this directive is associated with a response, users may
explicitly store such a response outside of the caching system (e.g.,
with a "Save As" dialog). History buffers may store such responses as
part of their normal operation.
The purpose of this directive is to meet the stated requirements of
certain users and service authors who are concerned about accidental
releases of information via unanticipated accesses to cache data
structures. While the use of this directive may improve privacy in
some cases, we caution that it is NOT in any way a reliable or
sufficient mechanism for ensuring privacy. In particular, malicious
or compromised caches may not recognize or obey this directive; and
communications networks may be vulnerable to eavesdropping.
14.9.3 Modifications of the Basic Expiration Mechanism
The expiration time of an entity may be specified by the origin
server using the Expires header (see section 14.21). Alternatively,
it may be specified using the max-age directive in a response.
If a response includes both an Expires header and a max-age
directive, the max-age directive overrides the Expires header, even
if the Expires header is more restrictive. This rule allows an origin
server to provide, for a given response, a longer expiration time to
an HTTP/1.1 (or later) cache than to an HTTP/1.0 cache. This may be
useful if certain HTTP/1.0 caches improperly calculate ages or
expiration times, perhaps due to desynchronized clocks.
Note: most older caches, not compliant with this specification, do
not implement any Cache-Control directives. An origin server
wishing to use a Cache-Control directive that restricts, but does
not prevent, caching by an HTTP/1.1-compliant cache may exploit the
requirement that the max-age directive overrides the Expires
header, and the fact that non-HTTP/1.1-compliant caches do not
observe the max-age directive.
Other directives allow an user agent to modify the basic expiration
mechanism. These directives may be specified on a request:
max-age
Indicates that the client is willing to accept a response whose age
is no greater than the specified time in seconds. Unless max-stale
directive is also included, the client is not willing to accept a
stale response.
min-fresh
Indicates that the client is willing to accept a response whose
freshness lifetime is no less than its current age plus the
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specified time in seconds. That is, the client wants a response
that will still be fresh for at least the specified number of
seconds.
max-stale
Indicates that the client is willing to accept a response that has
exceeded its expiration time. If max-stale is assigned a value,
then the client is willing to accept a response that has exceeded
its expiration time by no more than the specified number of
seconds. If no value is assigned to max-stale, then the client is
willing to accept a stale response of any age.
If a cache returns a stale response, either because of a max-stale
directive on a request, or because the cache is configured to
override the expiration time of a response, the cache MUST attach a
Warning header to the stale response, using Warning 10 (Response is
stale).
14.9.4 Cache Revalidation and Reload Controls
Sometimes an user agent may want or need to insist that a cache
revalidate its cache entry with the origin server (and not just with
the next cache along the path to the origin server), or to reload its
cache entry from the origin server. End-to-end revalidation may be
necessary if either the cache or the origin server has overestimated
the expiration time of the cached response. End-to-end reload may be
necessary if the cache entry has become corrupted for some reason.
End-to-end revalidation may be requested either when the client does
not have its own local cached copy, in which case we call it
"unspecified end-to-end revalidation", or when the client does have a
local cached copy, in which case we call it "specific end-to-end
revalidation."
The client can specify these three kinds of action using Cache-
Control request directives:
End-to-end reload
The request includes a "no-cache" Cache-Control directive or, for
compatibility with HTTP/1.0 clients, "Pragma: no-cache". No field
names may be included with the no-cache directive in a request. The
server MUST NOT use a cached copy when responding to such a
request.
Specific end-to-end revalidation
The request includes a "max-age=0" Cache-Control directive, which
forces each cache along the path to the origin server to revalidate
its own entry, if any, with the next cache or server. The initial
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request includes a cache-validating conditional with the client's
current validator.
Unspecified end-to-end revalidation
The request includes "max-age=0" Cache-Control directive, which
forces each cache along the path to the origin server to revalidate
its own entry, if any, with the next cache or server. The initial
request does not include a cache-validating conditional; the first
cache along the path (if any) that holds a cache entry for this
resource includes a cache-validating conditional with its current
validator.
When an intermediate cache is forced, by means of a max-age=0
directive, to revalidate its own cache entry, and the client has
supplied its own validator in the request, the supplied validator may
differ from the validator currently stored with the cache entry. In
this case, the cache may use either validator in making its own
request without affecting semantic transparency.
However, the choice of validator may affect performance. The best
approach is for the intermediate cache to use its own validator when
making its request. If the server replies with 304 (Not Modified),
then the cache should return its now validated copy to the client
with a 200 (OK) response. If the server replies with a new entity and
cache validator, however, the intermediate cache should compare the
returned validator with the one provided in the client's request,
using the strong comparison function. If the client's validator is
equal to the origin server's, then the intermediate cache simply
returns 304 (Not Modified). Otherwise, it returns the new entity with
a 200 (OK) response.
If a request includes the no-cache directive, it should not include
min-fresh, max-stale, or max-age.
In some cases, such as times of extremely poor network connectivity,
a client may want a cache to return only those responses that it
currently has stored, and not to reload or revalidate with the origin
server. To do this, the client may include the only-if-cached
directive in a request. If it receives this directive, a cache SHOULD
either respond using a cached entry that is consistent with the other
constraints of the request, or respond with a 504 (Gateway Timeout)
status. However, if a group of caches is being operated as a unified
system with good internal connectivity, such a request MAY be
forwarded within that group of caches.
Because a cache may be configured to ignore a server's specified
expiration time, and because a client request may include a max-stale
directive (which has a similar effect), the protocol also includes a
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mechanism for the origin server to require revalidation of a cache
entry on any subsequent use. When the must-revalidate directive is
present in a response received by a cache, that cache MUST NOT use
the entry after it becomes stale to respond to a subsequent request
without first revalidating it with the origin server. (I.e., the
cache must do an end-to-end revalidation every time, if, based solely
on the origin server's Expires or max-age value, the cached response
is stale.)
The must-revalidate directive is necessary to support reliable
operation for certain protocol features. In all circumstances an
HTTP/1.1 cache MUST obey the must-revalidate directive; in
particular, if the cache cannot reach the origin server for any
reason, it MUST generate a 504 (Gateway Timeout) response.
Servers should send the must-revalidate directive if and only if
failure to revalidate a request on the entity could result in
incorrect operation, such as a silently unexecuted financial
transaction. Recipients MUST NOT take any automated action that
violates this directive, and MUST NOT automatically provide an
unvalidated copy of the entity if revalidation fails.
Although this is not recommended, user agents operating under severe
connectivity constraints may violate this directive but, if so, MUST
explicitly warn the user that an unvalidated response has been
provided. The warning MUST be provided on each unvalidated access,
and SHOULD require explicit user confirmation.
The proxy-revalidate directive has the same meaning as the must-
revalidate directive, except that it does not apply to non-shared
user agent caches. It can be used on a response to an authenticated
request to permit the user's cache to store and later return the
response without needing to revalidate it (since it has already been
authenticated once by that user), while still requiring proxies that
service many users to revalidate each time (in order to make sure
that each user has been authenticated). Note that such authenticated
responses also need the public cache control directive in order to
allow them to be cached at all.
14.9.5 No-Transform Directive
Implementers of intermediate caches (proxies) have found it useful to
convert the media type of certain entity bodies. A proxy might, for
example, convert between image formats in order to save cache space
or to reduce the amount of traffic on a slow link. HTTP has to date
been silent on these transformations.
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Serious operational problems have already occurred, however, when
these transformations have been applied to entity bodies intended for
certain kinds of applications. For example, applications for medical
imaging, scientific data analysis and those using end-to-end
authentication, all depend on receiving an entity body that is bit
for bit identical to the original entity-body.
Therefore, if a response includes the no-transform directive, an
intermediate cache or proxy MUST NOT change those headers that are
listed in section 13.5.2 as being subject to the no-transform
directive. This implies that the cache or proxy must not change any
aspect of the entity-body that is specified by these headers.
14.9.6 Cache Control Extensions
The Cache-Control header field can be extended through the use of one
or more cache-extension tokens, each with an optional assigned value.
Informational extensions (those which do not require a change in
cache behavior) may be added without changing the semantics of other
directives. Behavioral extensions are designed to work by acting as
modifiers to the existing base of cache directives. Both the new
directive and the standard directive are supplied, such that
applications which do not understand the new directive will default
to the behavior specified by the standard directive, and those that
understand the new directive will recognize it as modifying the
requirements associated with the standard directive. In this way,
extensions to the Cache-Control directives can be made without
requiring changes to the base protocol.
This extension mechanism depends on a HTTP cache obeying all of the
cache-control directives defined for its native HTTP-version, obeying
certain extensions, and ignoring all directives that it does not
understand.
For example, consider a hypothetical new response directive called
"community" which acts as a modifier to the "private" directive. We
define this new directive to mean that, in addition to any non-shared
cache, any cache which is shared only by members of the community
named within its value may cache the response. An origin server
wishing to allow the "UCI" community to use an otherwise private
response in their shared cache(s) may do so by including
Cache-Control: private, community="UCI"
A cache seeing this header field will act correctly even if the cache
does not understand the "community" cache-extension, since it will
also see and understand the "private" directive and thus default to
the safe behavior.
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Unrecognized cache-directives MUST be ignored; it is assumed that any
cache-directive likely to be unrecognized by an HTTP/1.1 cache will
be combined with standard directives (or the response's default
cachability) such that the cache behavior will remain minimally
correct even if the cache does not understand the extension(s).
14.10 Connection
The Connection general-header field allows the sender to specify
options that are desired for that particular connection and MUST NOT
be communicated by proxies over further connections.
The Connection header has the following grammar:
Connection-header = "Connection" ":" 1#(connection-token)
connection-token = token
HTTP/1.1 proxies MUST parse the Connection header field before a
message is forwarded and, for each connection-token in this field,
remove any header field(s) from the message with the same name as the
connection-token. Connection options are signaled by the presence of
a connection-token in the Connection header field, not by any
corresponding additional header field(s), since the additional header
field may not be sent if there are no parameters associated with that
connection option. HTTP/1.1 defines the "close" connection option
for the sender to signal that the connection will be closed after
completion of the response. For example,
Connection: close
in either the request or the response header fields indicates that
the connection should not be considered `persistent' (section 8.1)
after the current request/response is complete.
HTTP/1.1 applications that do not support persistent connections MUST
include the "close" connection option in every message.
14.11 Content-Base
The Content-Base entity-header field may be used to specify the base
URI for resolving relative URLs within the entity. This header field
is described as Base in RFC 1808, which is expected to be revised.
Content-Base = "Content-Base" ":" absoluteURI
If no Content-Base field is present, the base URI of an entity is
defined either by its Content-Location (if that Content-Location URI
is an absolute URI) or the URI used to initiate the request, in that
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order of precedence. Note, however, that the base URI of the contents
within the entity-body may be redefined within that entity-body.
14.12 Content-Encoding
The Content-Encoding entity-header field is used as a modifier to the
media-type. When present, its value indicates what additional content
codings have been applied to the entity-body, and thus what decoding
mechanisms MUST be applied in order to obtain the media-type
referenced by the Content-Type header field. Content-Encoding is
primarily used to allow a document to be compressed without losing
the identity of its underlying media type.
Content-Encoding = "Content-Encoding" ":" 1#content-coding
Content codings are defined in section 3.5. An example of its use is
Content-Encoding: gzip
The Content-Encoding is a characteristic of the entity identified by
the Request-URI. Typically, the entity-body is stored with this
encoding and is only decoded before rendering or analogous usage.
If multiple encodings have been applied to an entity, the content
codings MUST be listed in the order in which they were applied.
Additional information about the encoding parameters MAY be provided
by other entity-header fields not defined by this specification.
14.13 Content-Language
The Content-Language entity-header field describes the natural
language(s) of the intended audience for the enclosed entity. Note
that this may not be equivalent to all the languages used within the
entity-body.
Content-Language = "Content-Language" ":" 1#language-tag
Language tags are defined in section 3.10. The primary purpose of
Content-Language is to allow a user to identify and differentiate
entities according to the user's own preferred language. Thus, if the
body content is intended only for a Danish-literate audience, the
appropriate field is
Content-Language: da
If no Content-Language is specified, the default is that the content
is intended for all language audiences. This may mean that the sender
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does not consider it to be specific to any natural language, or that
the sender does not know for which language it is intended.
Multiple languages MAY be listed for content that is intended for
multiple audiences. For example, a rendition of the "Treaty of
Waitangi," presented simultaneously in the original Maori and English
versions, would call for
Content-Language: mi, en
However, just because multiple languages are present within an entity
does not mean that it is intended for multiple linguistic audiences.
An example would be a beginner's language primer, such as "A First
Lesson in Latin," which is clearly intended to be used by an
English-literate audience. In this case, the Content-Language should
only include "en".
Content-Language may be applied to any media type -- it is not
limited to textual documents.
14.14 Content-Length
The Content-Length entity-header field indicates the size of the
message-body, in decimal number of octets, sent to the recipient or,
in the case of the HEAD method, the size of the entity-body that
would have been sent had the request been a GET.
Content-Length = "Content-Length" ":" 1*DIGIT
An example is
Content-Length: 3495
Applications SHOULD use this field to indicate the size of the
message-body to be transferred, regardless of the media type of the
entity. It must be possible for the recipient to reliably determine
the end of HTTP/1.1 requests containing an entity-body, e.g., because
the request has a valid Content-Length field, uses Transfer-Encoding:
chunked or a multipart body.
Any Content-Length greater than or equal to zero is a valid value.
Section 4.4 describes how to determine the length of a message-body
if a Content-Length is not given.
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Note: The meaning of this field is significantly different from the
corresponding definition in MIME, where it is an optional field
used within the "message/external-body" content-type. In HTTP, it
SHOULD be sent whenever the message's length can be determined
prior to being transferred.
14.15 Content-Location
The Content-Location entity-header field may be used to supply the
resource location for the entity enclosed in the message. In the case
where a resource has multiple entities associated with it, and those
entities actually have separate locations by which they might be
individually accessed, the server should provide a Content-Location
for the particular variant which is returned. In addition, a server
SHOULD provide a Content-Location for the resource corresponding to
the response entity.
Content-Location = "Content-Location" ":"
( absoluteURI | relativeURI )
If no Content-Base header field is present, the value of Content-
Location also defines the base URL for the entity (see section
14.11).
The Content-Location value is not a replacement for the original
requested URI; it is only a statement of the location of the resource
corresponding to this particular entity at the time of the request.
Future requests MAY use the Content-Location URI if the desire is to
identify the source of that particular entity.
A cache cannot assume that an entity with a Content-Location
different from the URI used to retrieve it can be used to respond to
later requests on that Content-Location URI. However, the Content-
Location can be used to differentiate between multiple entities
retrieved from a single requested resource, as described in section
13.6.
If the Content-Location is a relative URI, the URI is interpreted
relative to any Content-Base URI provided in the response. If no
Content-Base is provided, the relative URI is interpreted relative to
the Request-URI.
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14.16 Content-MD5
The Content-MD5 entity-header field, as defined in RFC 1864 [23], is
an MD5 digest of the entity-body for the purpose of providing an
end-to-end message integrity check (MIC) of the entity-body. (Note: a
MIC is good for detecting accidental modification of the entity-body
in transit, but is not proof against malicious attacks.)
Content-MD5 = "Content-MD5" ":" md5-digest
md5-digest = <base64 of 128 bit MD5 digest as per RFC 1864>
The Content-MD5 header field may be generated by an origin server to
function as an integrity check of the entity-body. Only origin
servers may generate the Content-MD5 header field; proxies and
gateways MUST NOT generate it, as this would defeat its value as an
end-to-end integrity check. Any recipient of the entity-body,
including gateways and proxies, MAY check that the digest value in
this header field matches that of the entity-body as received.
The MD5 digest is computed based on the content of the entity-body,
including any Content-Encoding that has been applied, but not
including any Transfer-Encoding that may have been applied to the
message-body. If the message is received with a Transfer-Encoding,
that encoding must be removed prior to checking the Content-MD5 value
against the received entity.
This has the result that the digest is computed on the octets of the
entity-body exactly as, and in the order that, they would be sent if
no Transfer-Encoding were being applied.
HTTP extends RFC 1864 to permit the digest to be computed for MIME
composite media-types (e.g., multipart/* and message/rfc822), but
this does not change how the digest is computed as defined in the
preceding paragraph.
Note: There are several consequences of this. The entity-body for
composite types may contain many body-parts, each with its own MIME
and HTTP headers (including Content-MD5, Content-Transfer-Encoding,
and Content-Encoding headers). If a body-part has a Content-
Transfer-Encoding or Content-Encoding header, it is assumed that
the content of the body-part has had the encoding applied, and the
body-part is included in the Content-MD5 digest as is -- i.e.,
after the application. The Transfer-Encoding header field is not
allowed within body-parts.
Note: while the definition of Content-MD5 is exactly the same for
HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
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in which the application of Content-MD5 to HTTP entity-bodies
differs from its application to MIME entity-bodies. One is that
HTTP, unlike MIME, does not use Content-Transfer-Encoding, and does
use Transfer-Encoding and Content-Encoding. Another is that HTTP
more frequently uses binary content types than MIME, so it is worth
noting that, in such cases, the byte order used to compute the
digest is the transmission byte order defined for the type. Lastly,
HTTP allows transmission of text types with any of several line
break conventions and not just the canonical form using CRLF.
Conversion of all line breaks to CRLF should not be done before
computing or checking the digest: the line break convention used in
the text actually transmitted should be left unaltered when
computing the digest.
14.17 Content-Range
The Content-Range entity-header is sent with a partial entity-body to
specify where in the full entity-body the partial body should be
inserted. It also indicates the total size of the full entity-body.
When a server returns a partial response to a client, it must
describe both the extent of the range covered by the response, and
the length of the entire entity-body.
Content-Range = "Content-Range" ":" content-range-spec
content-range-spec = byte-content-range-spec
byte-content-range-spec = bytes-unit SP first-byte-pos "-"
last-byte-pos "/" entity-length
entity-length = 1*DIGIT
Unlike byte-ranges-specifier values, a byte-content-range-spec may
only specify one range, and must contain absolute byte positions for
both the first and last byte of the range.
A byte-content-range-spec whose last-byte-pos value is less than its
first-byte-pos value, or whose entity-length value is less than or
equal to its last-byte-pos value, is invalid. The recipient of an
invalid byte-content-range-spec MUST ignore it and any content
transferred along with it.
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Examples of byte-content-range-spec values, assuming that the entity
contains a total of 1234 bytes:
o The first 500 bytes:
bytes 0-499/1234
o The second 500 bytes:
bytes 500-999/1234
o All except for the first 500 bytes:
bytes 500-1233/1234
o The last 500 bytes:
bytes 734-1233/1234
When an HTTP message includes the content of a single range (for
example, a response to a request for a single range, or to a request
for a set of ranges that overlap without any holes), this content is
transmitted with a Content-Range header, and a Content-Length header
showing the number of bytes actually transferred. For example,
HTTP/1.1 206 Partial content
Date: Wed, 15 Nov 1995 06:25:24 GMT
Last-modified: Wed, 15 Nov 1995 04:58:08 GMT
Content-Range: bytes 21010-47021/47022
Content-Length: 26012
Content-Type: image/gif
When an HTTP message includes the content of multiple ranges (for
example, a response to a request for multiple non-overlapping
ranges), these are transmitted as a multipart MIME message. The
multipart MIME content-type used for this purpose is defined in this
specification to be "multipart/byteranges". See appendix 19.2 for its
definition.
A client that cannot decode a MIME multipart/byteranges message
should not ask for multiple byte-ranges in a single request.
When a client requests multiple byte-ranges in one request, the
server SHOULD return them in the order that they appeared in the
request.
If the server ignores a byte-range-spec because it is invalid, the
server should treat the request as if the invalid Range header field
Fielding, et. al. Standards Track [Page 115]
RFC 2068 HTTP/1.1 January 1997
did not exist. (Normally, this means return a 200 response containing
the full entity). The reason is that the only time a client will make
such an invalid request is when the entity is smaller than the entity
retrieved by a prior request.
14.18 Content-Type
The Content-Type entity-header field indicates the media type of the
entity-body sent to the recipient or, in the case of the HEAD method,
the media type that would have been sent had the request been a GET.
Content-Type = "Content-Type" ":" media-type
Media types are defined in section 3.7. An example of the field is
Content-Type: text/html; charset=ISO-8859-4
Further discussion of methods for identifying the media type of an
entity is provided in section 7.2.1.
14.19 Date
The Date general-header field represents the date and time at which
the message was originated, having the same semantics as orig-date in
RFC 822. The field value is an HTTP-date, as described in section
3.3.1.
Date = "Date" ":" HTTP-date
An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT
If a message is received via direct connection with the user agent
(in the case of requests) or the origin server (in the case of
responses), then the date can be assumed to be the current date at
the receiving end. However, since the date--as it is believed by the
origin--is important for evaluating cached responses, origin servers
MUST include a Date header field in all responses. Clients SHOULD
only send a Date header field in messages that include an entity-
body, as in the case of the PUT and POST requests, and even then it
is optional. A received message which does not have a Date header
field SHOULD be assigned one by the recipient if the message will be
cached by that recipient or gatewayed via a protocol which requires a
Date.
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