Byte Range Requests allow partial content requests, which is especially useful for large media files when it is desired to download only a specific portion of the. For example, if the Web server and browser support byte serving, Acrobat files (PDF files) can be viewed as soon as the first couple of pages have been. An origin server that supports byte-range requests for a given target A client can wait to check if the server support range request or he can html5 - Does iPhone/iPad Safari require 'Accept-Ranges' header for.
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For example, a user byte serving processing a large representation with an internal catalog of parts might need to request later parts first, particularly if the representation consists of pages stored in reverse order and the user agent wishes to transfer one page at a time.
Byte Range Requests / Byte Serving
The Range header field is evaluated after evaluating the precondition header fields defined in [ RFC ], and only if the result in absence of the Range header field would be a OK response. If all of the preconditions are true, the server supports the Range header field for the target resource, and the specified range s are valid and satisfiable as defined in Section 2.
If all of the preconditions are true, byte serving server supports the Range header field for the target resource, and the specified range s are invalid or unsatisfiable, the server SHOULD send a Range Not Satisfiable response.
If-Range If a client has a partial copy of a representation and wishes to have an up-to-date copy of the entire representation, it could use the Range header field with a conditional GET using either or both of If-Unmodified-Since and If-Match.
Byte serving Definition from PC Magazine Encyclopedia
However, if the precondition fails because the representation has been modified, the client would then have to make a second request to obtain the entire current representation. The "If-Range" header field allows a client to "short-circuit" the second request.
Informally, its meaning is as follows: An origin server MUST ignore an If-Range header field received in a request for a target byte serving that does not support Range requests. If the validator given in the If-Range header field matches the current validator for the selected representation of the target resource, then the server SHOULD process the Range header field as requested.
Note that this comparison by exact match, including when the validator is an HTTP-date, differs from the "earlier than or equal to" comparison used when evaluating an If-Unmodified-Since conditional.
Responses to a Range Request 4. If a single part is being transferred, the server generating the response MUST generate a Content-Range header field, describing what range of the selected representation is enclosed, and a payload consisting of the range.
Byte serving - Wikipedia
Wed, 15 Nov A server MUST NOT generate a multipart response to a request for a single range, since a client that does not request multiple parts might not support multipart responses. When a multipart response payload is generated, the server SHOULD send the parts in byte serving same order that the corresponding byte-range-spec appeared in the received Range header field, Fielding, et al.
A client that receives a multipart response MUST inspect the Content-Range header field present in each body part in order to determine which range is contained in that body part; a client cannot rely on receiving byte serving same ranges that it requested, nor the same order that it requested.
When a response is generated, the server MUST generate the following header fields, in addition to those required above, if the field would have been sent in a OK response to the same request: If a is generated in response to a request with an If-Range header field, the sender SHOULD NOT generate other representation header fields beyond those required above, because the client is understood to already have a prior response containing those header fields.
Otherwise, the sender MUST generate all of the representation header fields that would have been sent in a OK response to the same request. A response is cacheable by default; i.
Content-Range The "Content-Range" byte serving field is sent in a single part Partial Content response to indicate the partial range of the selected representation enclosed as the message payload, sent in each part of a multipart response byte serving indicate the range enclosed within each body part, and sent in Range Not Satisfiable responses to provide information about the selected representation.
For byte ranges, a sender SHOULD byte serving the complete length of the representation from which the range has been extracted, unless the complete length is unknown or difficult to determine. The following example illustrates when the complete length of the selected representation is known by the sender to be bytes: The Content-Range header field has no meaning for status codes that do not explicitly describe its semantic.
Combining Ranges A response might transfer only a subrange of a representation if the connection closed prematurely or if the request used one byte serving more Range specifications. After several such transfers, a client might have received several ranges of the same representation. A client that has received multiple partial responses to GET requests on a target resource MAY combine those responses into a larger continuous range if they share the same strong validator.
If the most recent response is an incomplete OK response, then the header fields of that response are used for any combined response and replace those of the matching stored responses.
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If the most recent response is a Partial Content response and at least one of the matching stored responses is a OKthen the combined response header fields consist of the most recent response's header fields. If all of the matching stored responses are responses, then the stored response with the most recent header fields is used as the source of header fields for the combined response, except that the client MUST use other header fields provided in the byte serving response, aside byte serving Content-Range, to replace all instances of the corresponding header fields in the stored response.
If the union consists of the entire range of the representation, then the client MUST process the combined response as if it were a complete OK response, including a Content-Length header field that reflects the byte serving length.
Otherwise, the byte serving MUST process the set of continuous ranges as one of the following: