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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 MUST be forwarded by transparent 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 might 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.
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 URI used to identify
the resource. If the media type remains unknown, the recipient SHOULD treat it as type “application/octet-
stream”.
7.2.2 Entity Length
The entity-length of a message is the length of the message-body before any transfer-codings have been applied.
Section 4.4 defines how the transfer-length of a message-body is determined.
8 Connections
8.1 Persistent Connections
8.1.1 Purpose
Prior to persistent connections, a separate TCP connection was established to fetch each URL, increasing the load on
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