The HTTP 428 status code happens when a server requires a client to use a conditional request.
HTTP supports conditional requests (requests that contain one or more If- headers), which are often used in caching. Conditional requests can also be used to verify the integrity of files via checksums.
It can be useful when a client wants to update a resource it retrieved a while back. While the client has been making changes, the file could have been updated or deleted in the meantime (lost update problem is the term-of-art). By forcing clients to use a conditional request, the server minimizes the risk of conflicts.
PUT /upload HTTP/2
The server should reply with instructions on how to resubmit the request correctly. In most cases, you’d have to include the If-Match header.
HTTP/2 428 Precondition Required
See also
- 412 Precondition Failed - a status code server uses when one or more preconditions aren’t met.
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