206 Partial Content

   The server has fulfilled the partial GET request for the resource.
   The request MUST have included a Range header field (section 14.35)
   indicating the desired range, and MAY have included an If-Range
   header field (section 14.27) to make the request conditional.

   The response MUST include the following header fields:

      - Either a Content-Range header field (section 14.16) indicating
        the range included with this response, or a multipart/byteranges
        Content-Type including Content-Range fields for each part. If a
        Content-Length header field is present in the response, its
        value MUST match the actual number of OCTETs transmitted in the
        message-body.

      - Date

      - ETag and/or Content-Location, if the header would have been sent
        in a 200 response to the same request

      - Expires, Cache-Control, and/or Vary, if the field-value might
        differ from that sent in any previous response for the same
        variant

   If the 206 response is the result of an If-Range request that used a
   strong cache validator (see section 13.3.3), the response SHOULD NOT
   include other entity-headers. If the response is the result of an
   If-Range request that used a weak validator, the response MUST NOT
   include other entity-headers; this prevents inconsistencies between
   cached entity-bodies and updated headers. Otherwise, the response
   MUST include all of the entity-headers that would have been returned
   with a 200 (OK) response to the same request.

   A cache MUST NOT combine a 206 response with other previously cached
   content if the ETag or Last-Modified headers do not match exactly,
   see 13.5.4.

   A cache that does not support the Range and Content-Range headers
   MUST NOT cache 206 (Partial) responses.