Our app's setup.xml page uses a custom EAI endpoint. I know when we throw an exception from the handleEdit method, the setup page will refuse to save and the exception's message will be displayed in red text at the top of the screen.
But what if we only want to display a "warning" message to users, but without preventing the user from saving settings? Is there a way, in our EAI endpoint, to display a message at the top of the screen without throwing an exception and preventing saving?
Ideally, our message would show up with a yellow background, but the blue-background regular message is OK too.
Currently this is not possible. Extending the messages endpoint to allow posting from outside of splunkd would be easy to do - I recommend filing an ER for this.
Although shoving a message into the top of the screen isn't possible (yet), per Amrit's answer, another option could be to log warnings to a log file (even Splunk's internal log) and then to pull messages out of that log when the app's home page is displayed.
Since the default action after running setup is (or should be!) running the app, the user will see the warning and will be able to re-run setup if needed.
I take it back - this IS possible now. Try it out by posting to /services/messages with the parameters "name" and "value"!
$ splunk _internal call /messages -post:name FOO -post:value "haaay you guyyyyyysss"