Arvados

For collections (and possibly other record updates) we would like to be able to send updates with "If-Match" header to confirm that the version we are updating is the same version we read. If the If-Match fails (the etag of the record has changed) then the update is rejected and the client must re-read the record and retry.

Consult the HTTP 1.1 RFCs for rules about etag and If-Match (such as the appropriate error code).

See also https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-Match