If-Match HTTP request header makes the request conditional. For
HEAD methods, the server will send back the requested resource only if it matches one of the listed
PUT and other non-safe methods, it will only upload the resource in this case.
The comparison with the stored
ETag uses the strong comparison algorithm, meaning two files are considered identical byte to byte only. If a listed
ETag has the
W/ prefix indicating a weak entity tag, it will never match under this comparison algorithm.
There are two common use cases:
HEADmethods, used in combination with a
Rangeheader, it can guarantee that the new ranges requested comes from the same resource than the previous one. If it doesn't match, then a
416(Range Not Satisfiable) response is returned.
- For other methods, and in particular for
If-Matchcan be used to prevent the lost update problem. It can check if the modification of a resource that the user wants to upload will not override another change that has been done since the original resource was fetched. If the request cannot be fulfilled, the
412(Precondition Failed) response is returned.
|Header type||Request header|
|Forbidden header name||no|
If-Match: <etag_value> If-Match: <etag_value>, <etag_value>, …
- Entity tags uniquely representing the requested resources. They are a string of ASCII characters placed between double quotes (like
"675af34563dc-tr34"). They may be prefixed by
W/to indicate that they are "weak", i.e. that they represent the resource semantically, but not byte-for-byte. However, in an
If-Matchheader, weak entity tags will never match.
- The asterisk is a special value representing any resource.
If-Match: "bfc13a64729c4290ef5b2c2730249c88ca92d82d" If-Match: "67ab43", "54ed21", "7892dd" If-Match: *
|RFC 7232, section 3.1: If-Match||Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests|
The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
|Chrome Full support Yes||Edge Full support 12||Firefox Full support Yes||IE Full support Yes||Opera Full support Yes||Safari Full support Yes||WebView Android Full support Yes||Chrome Android Full support Yes||Firefox Android Full support Yes||Opera Android Full support Yes||Safari iOS Full support Yes||Samsung Internet Android Full support Yes|
- Full support
- Full support