RFC 2068 HTTP/1.1 January 1997
6.2 Response Header Fields
The response-header fields allow the server to pass additional
information about the response which cannot be placed in the Status-
Line. These header fields give information about the server and about
further access to the resource identified by the Request-URI.
response-header = Age ; Section 14.6
| Location ; Section 14.30
| Proxy-Authenticate ; Section 14.33
| Public ; Section 14.35
| Retry-After ; Section 14.38
| Server ; Section 14.39
| Vary ; Section 14.43
| Warning ; Section 14.45
| WWW-Authenticate ; Section 14.46
Response-header field names can be extended reliably only in
combination with a change in the protocol version. However, new or
experimental header fields MAY be given the semantics of response-
header fields if all parties in the communication recognize them to
be response-header fields. Unrecognized header fields are treated as
entity-header fields.
7 Entity
Request and Response messages MAY transfer an entity if not otherwise
restricted by the request method or response status code. An entity
consists of entity-header fields and an entity-body, although some
responses will only include the entity-headers.
In this section, both sender and recipient refer to either the client
or the server, depending on who sends and who receives the entity.
7.1 Entity Header Fields
Entity-header fields define optional metainformation about the
entity-body or, if no body is present, about the resource identified
by the request.
Fielding, et. al. Standards Track [Page 41]
RFC 2068 HTTP/1.1 January 1997
entity-header = Allow ; Section 14.7
| Content-Base ; Section 14.11
| Content-Encoding ; Section 14.12
| Content-Language ; Section 14.13
| Content-Length ; Section 14.14
| Content-Location ; Section 14.15
| Content-MD5 ; Section 14.16
| Content-Range ; Section 14.17
| Content-Type ; Section 14.18
| ETag ; Section 14.20
| Expires ; Section 14.21
| Last-Modified ; Section 14.29
| extension-header
extension-header = message-header
The extension-header mechanism allows additional entity-header fields
to be defined without changing the protocol, but these fields cannot
be assumed to be recognizable by the recipient. Unrecognized header
fields SHOULD be ignored by the recipient and forwarded by proxies.
7.2 Entity Body
The entity-body (if any) sent with an HTTP request or response is in
a format and encoding defined by the entity-header fields.
entity-body = *OCTET
An entity-body is only present in a message when a message-body is
present, as described in section 4.3. The entity-body is obtained
from the message-body by decoding any Transfer-Encoding that may have
been applied to ensure safe and proper transfer of the message.
7.2.1 Type
When an entity-body is included with a message, the data type of that
body is determined via the header fields Content-Type and Content-
Encoding. These define a two-layer, ordered encoding model:
entity-body := Content-Encoding( Content-Type( data ) )
Content-Type specifies the media type of the underlying data.
Content-Encoding may be used to indicate any additional content
codings applied to the data, usually for the purpose of data
compression, that are a property of the requested resource. There is
no default encoding.
Fielding, et. al. Standards Track [Page 42]
RFC 2068 HTTP/1.1 January 1997
Any HTTP/1.1 message containing an entity-body SHOULD include a
Content-Type header field defining the media type of that body. If
and only if the media type is not given by a Content-Type field, the
recipient MAY attempt to guess the media type via inspection of its
content and/or the name extension(s) of the URL used to identify the
resource. If the media type remains unknown, the recipient SHOULD
treat it as type "application/octet-stream".
7.2.2 Length
The length of an entity-body is the length of the message-body after
any transfer codings have been removed. Section 4.4 defines how the
length of a message-body is determined.