If the request is a single value, we already know, so if we also
know that the function returned a single-valued type, then we can
render the single value, instead of an array with a single item.
See gh-36
These can be used to more reliably discover whether the user
has declared a function with flux types or "bare" POJOs. They
then pave the way to supporting single valued types in a special
way.
Also consolidate and simplify the logic in FunctionInspector
So that single Strings can be POSTed without JSON conversion.
There's still some work to do to support single POJOs in JSON, and
to reach parity with the WebFlux reactive type handlers, but it's
now closer to what we had before we moved the String conversion
out of the function layer.
There is one behaviour change (you have to POST an array to a function
endpoint if you are sending a body), and also a message converter that
needed to be removed so that arrays are not toStringed in the response
body.
When the user has sent us a single value, we can make the signature
of the handler and the format of the HTTP response much more
natural if it is single valued too (i.e. a Mono).
An HTTP response does not have to be an infinite stream, and in fact
life is simpler if it is not. The timeout in the web wrappers can
be used to close the response and return normally to a client
that has been waiting more than (say) 1s, instead of treating
it as an error condition.
Error handling is still kind of unsolved.
If user sends "Accept: */*" we don't want to default to sending
an SSE (for instance). So the logic for detecting those preferences
has to take MediaType.ALL into account as a special case.
We don't need to cover all the possible uses of Flux (only
Flux<String> really), so this isn't comprehensive coverage of
all the features in Spring WebFlux, but it's good enough for
functions to run with Spring Boot 1.5.
Should be easy enoug hto add back later, but it was causing issues
with type conversion where we are npot yet sophisticated enough
to chain functions together and keep track of the types being
passed between them.
User can POST to web endpoint in SSE style, i.e:
HTTP/1.1
Content-Type: text/event-stream
data:foo
data:bar
Will be converted to a Flux with values foo and bar
Make it deployable via its maven coordinates in
spring-cloud-function-deployer (it is deployed by default on start
up right now, but that's just a demo)
