A conditional request is a request that may be executed differently depending on the value of specific HTTP headers. These headers define the precondition that must be true before the server should execute the request. With respect to entity tags, we have two options for making requests conditional.
- If-Match: The request will succeed if the ETag of the remote resource is equal to the one listed in this header.
- If-None-Match: The request will succeed if the ETag of the remote resource is different to each listed in this header.
By specifying the appropriate
ETagand condition header, you can perform optimistic locking for concurrent operations on a resource. Let’s walk through an example of how this works in practice.
Read on for more details.