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Range Requests

HTTP range requests allow sending only a portion of an HTTP message from a server to a client. Useful for large media or downloading files with pause and resume functions (MDN).

Response headers

Accept-Ranges

Indicates what range unit is supported. Specify none (doesn't support range request) or bytes (supports range request).

Accept-Ranges: bytes
Accept-Ranges: none

Content-Range

Indicates the range of bytes sent from the full document (e.g. Content-Range: bytes 200-1000/67589). Accompanies a 206 (Partial Content) response.

Content-Range: <unit> <range-start>-<range-end>/<size>
Content-Range: <unit> <range-start>-<range-end>/*
Content-Range: <unit> */<size>

Request headers

Range

Request data for the specified range(s). Expects the server to respond with 206 (Partial Content), 416 (Range Not Satisfiable), or 200 (OK) (if the server ignores the Range and returns the whole document).

  • bytes=200-1000, 2000-6576, 19000- — request for this ranges
  • bytes=0-499, -500 — request for the first 500 and the last 500 bytes
Range: <unit>=<range-start>-
Range: <unit>=<range-start>-<range-end>
Range: <unit>=<range-start>-<range-end>, ...
Range: <unit>=-<suffix-length>

If-Range

Make the range request conditional:

  • if the document has not been changed: respond with a 206 (Partial Content) and send the part(s) that is being requesting in Range
  • otherwise: respond with 200 (OK) and send the entire document

The most common use case is to resume a download (MDN).

You can specify the value of If-Range with a Last-Modified timestamp (e.g. Wed, 21 Oct 2015 07:28:00 GMT) or an ETag value.

If-Range: <day-name>, <day> <month> <year> <hour>:<minute>:<second> GMT
If-Range: <etag>

References