Hello Martin,

Thank you for a good question. Normally, the write service does not return until it writes the values or determines that the value cannot be written. So, the normal case is that the client side write method will return true or throw an exception in case of failure.

The OPC UA specification takes into account many possible application scenarios. In certain cases, the server will successfully write to an intermediate system, and will not know if the data source was updated properly. In these cases, the server should report a success code that indicates that the write was not verified. This is the status code Good_CompletesAsynchronously. In the client side SDK write method, the return value false means that server responded with Good_CompletesAsynchronously.

One question was that: “Can I get a response when the write is actually done?”. According to my understanding, if the server returns Good_CompletesAsynchronously, you don’t have any way to know more information about that specific write request status. One option would be to read the value to make sure the value has changed.

Other question was that “Are subsequent write-requests guaranteed to be written in order to the server?”
If the server responds with status code Good_CompletesAsynchronously, then it’s basically up to the intermediate system to make sure that the value is written correctly. So, it’s application specific how this external system works. If you have some server application that returns these status codes, then you should study the server documentation to see what the status code means in that specific system.