If-Range

The If-Range HTTP request header makes a range request conditional: if the condition is fulfilled, the range request is issued, and the server sends back a 206 Partial Content answer with the appropriate 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, to guarantee that the stored resource has not been modified since the last fragment has been received.

Header type	Request header
Forbidden header name	no

Syntax

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

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

Specifications

Specification
Hypertext Transfer Protocol (HTTP/1.1): Range Requests # header.if-range

Browser compatibility

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