HTTP Entity Headers
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Describes any optional method that may have been used to encode the entity. This header is most often used when transferring entities that have been compressed; it tells the recipient what algorithm has been used so the entity can be uncompressed. Note that this header only describes transformations performed on the entity in a message; the Transfer-Encoding header describes encodings done on the message as a whole. See the topic on content codings and transfer codings for more details.
Specifies the natural (human) language intended for using the entity. This is an optional header, and may not be appropriate for all resource types. Multiple languages may be specified, if needed.
This header is intended to provide guidance so the entity can be presented to the correct audience; thus, the language should be selected based on who would best use the material, which may not necessarily include all of the languages used in the entity. For example, a German analysis of Italian operas would probably best tagged only with the language de. (They do have German analyses of Italian operas, dont they? J)
Indicates the size of the entity in octets. This header is important, as it is used by the recipient to determine the end of a message. However, it may only be included in cases where the length of a message can be fully determined prior to transmitting the entity. This is not always possible in the case of dynamically-generated content, which complicates message length calculation; the discussion of data length and the chunked transfer encoding contains a full exploration of this issue.
Specifies the resource location of the entity, in the form of an absolute or relative uniform resource locator (URL). This is an optional header, and is normally included only in cases where the entity has been supplied from a location different from the one specified in the request. This may occur if a particular resource is stored in multiple places.
Contains an MD5 digest for the entity, used for message integrity checking.
Sent when a message contains an entity that is only part of a complete resource; for example, a fragment of a file sent in response to an HTTP GET request containing the Range header. The Content-Range header Indicates what portion of the overall file this message contains, as well as the total size of the resource. This information is given as a byte range, with the first byte numbered 0; for example, if the entity contains the first 1,200 bytes of a 2,000-byte file, this header would have a value of 0-1199/2000.
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