14.36 Range

14.36.1 Byte Ranges

   Since all HTTP entities are represented in HTTP messages as sequences
   of bytes, the concept of a byte range is meaningful for any HTTP
   entity.  (However, not all clients and servers need to support byte-
   range operations.)

   Byte range specifications in HTTP apply to the sequence of bytes in
   the entity-body (not necessarily the same as the message-body).

   A byte range operation may specify a single range of bytes, or a set
   of ranges within a single entity.

       ranges-specifier = byte-ranges-specifier

       byte-ranges-specifier = bytes-unit "=" byte-range-set

       byte-range-set  = 1#( byte-range-spec | suffix-byte-range-spec )

       byte-range-spec = first-byte-pos "-" [last-byte-pos]

       first-byte-pos  = 1*DIGIT

       last-byte-pos   = 1*DIGIT

   The first-byte-pos value in a byte-range-spec gives the byte-offset
   of the first byte in a range. The last-byte-pos value gives the
   byte-offset of the last byte in the range; that is, the byte
   positions specified are inclusive. Byte offsets start at zero.





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   If the last-byte-pos value is present, it must be greater than or
   equal to the first-byte-pos in that byte-range-spec, or the byte-
   range-spec is invalid. The recipient of an invalid byte-range-spec
   must ignore it.

   If the last-byte-pos value is absent, or if the value is greater than
   or equal to the current length of the entity-body, last-byte-pos is
   taken to be equal to one less than the current length of the entity-
   body in bytes.

   By its choice of last-byte-pos, a client can limit the number of
   bytes retrieved without knowing the size of the entity.

          suffix-byte-range-spec = "-" suffix-length

          suffix-length = 1*DIGIT

   A suffix-byte-range-spec is used to specify the suffix of the
   entity-body, of a length given by the suffix-length value. (That is,
   this form specifies the last N bytes of an entity-body.) If the
   entity is shorter than the specified suffix-length, the entire
   entity-body is used.

   Examples of byte-ranges-specifier values (assuming an entity-body of
   length 10000):

     o  The first 500 bytes (byte offsets 0-499, inclusive):

          bytes=0-499

     o  The second 500 bytes (byte offsets 500-999, inclusive):

          bytes=500-999

     o  The final 500 bytes (byte offsets 9500-9999, inclusive):

          bytes=-500

     o  Or

          bytes=9500-

     o  The first and last bytes only (bytes 0 and 9999):

          bytes=0-0,-1






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RFC 2068                        HTTP/1.1                    January 1997


     o  Several legal but not canonical specifications of the second
        500 bytes (byte offsets 500-999, inclusive):

          bytes=500-600,601-999

          bytes=500-700,601-999