If-Range

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

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The HTTP If-Range request header makes a range request conditional. If the condition is fulfilled, a range request is issued, and the server sends back a 206 Partial Content response with part (or parts) of the resource in the body. If the condition is not fulfilled, the full resource is sent back with a 200 OK status.

This header can be used either with the Last-Modified validator or with ETag, but not with both.

The most common use case is to resume a download with guarantees that the resource on the server has not been modified since the last part has been received by the client.

Header type	Request header
Forbidden request header	No

Syntax

http

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

Directives

<etag>: An entity tag uniquely representing the requested resource. It is a string of ASCII characters placed between double quotes (Like "675af34563dc-tr34"). A weak entity tag (one prefixed by W/) must not be used in this header.
<day-name>: One of Mon, Tue, Wed, Thu, Fri, Sat, or Sun (case-sensitive).
<day>: 2 digit day number, e.g., "04" or "23".
<month>: One of Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec (case sensitive).
<year>: 4 digit year number, e.g., "1990" or "2016".
<hour>: 2 digit hour number, e.g., "09" or "23".
<minute>: 2 digit minute number, e.g., "04" or "59".
<second>: 2 digit second number, e.g., "04" or "59".
GMT: Greenwich Mean Time. HTTP dates are always expressed in GMT, never in local time.

Examples

http

If-Range: Wed, 21 Oct 2015 07:28:00 GMT

If-Range: "67ab43"

Specifications

Specification
HTTP Semantics # field.if-range