ContentRangeHeader

ContentRangeHeader, formally the Content-Range HTTP header, is used by a server to describe a partial delivery of a resource. It is sent in responses that fulfill a Range request or in multipart responses that deliver subranges of a resource. The header is most commonly associated with byte-range requests and the 206 Partial Content status code, signaling that only a portion of the resource is being transferred.

The syntax of the header is Content-Range: unit start-end/size. The unit is typically bytes. A common form is Content-Range: bytes 200-999/67589, indicating that bytes 200 through 999 (inclusive) are being sent out of a total size of 67,589 bytes. If the total size is unknown, the slash-portion may use an asterisk: Content-Range: bytes 200-999/*.

The meaning of the values is straightforward: start and end specify the inclusive byte positions of the delivered portion within the full resource. The size after the slash indicates the total size of the resource, or is asterisk if unknown. In multipart responses (such as when multiple ranges are requested), multiple parts are sent, each with its own Content-Range line within the multipart body.

Content-Range is complementary to the Range request header. The client sends Range headers to request specific byte ranges, and the server responds with Content-Range to indicate what portion was returned. Servers may also include Accept-Ranges to advertise support. If a request asks for an invalid range, the server may respond with 416 Range Not Satisfiable.