Fix connection leak in rest proxy when return type is void or mono<void>

[kasobol-msft]

Caught in perf pipelines.

Rest Proxy would leak connections if interface method returns void or Mono like this

azure-sdk-for-java/sdk/core/azure-core-perf/src/main/java/com/azure/core/perf/core/MyRestProxyService.java

Lines 39 to 43 in cf1b7dc

	@Put("BinaryData/{id}")
	Mono<Void> setBinaryData(@HostParam("$host") String endpoint,
	@PathParam("id") String id,
	@BodyParam("application/octet-stream") BinaryData body,
	@HeaderParam("Content-Length") long length);

The symptoms were perf of OkHttp client grossly underperforming in core perf pipeline. Attempt to reproduce revealed OkHttp complaining about undisposed responses.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[mikeharder]

Just curious, why is the new code better?

[kasobol-msft]

The binaryDataSupplier is supposed to supply fresh BinaryData for each runAsync.
The old code is effectively doing that, but only because the caller uses flatMap - which is just luck rather than proper reactive stream.
Wrapping the supplier in Mono makes it properly reactive, i.e. subscriber triggers binary data creation regardless of what caller of this is doing.

[alzimmermsft]

Should this be doOnNext or doOnSuccess? Does Mono<Void> emit a next or does it only emit completion?

This applies to the void scenario below as well.

[kasobol-msft]

asyncExpectedResponse is Mono<Mono<HttpResponseDecoder.HttpDecodedResponse> when we add that operator.
doOnSuccess would be kind of same here, but we'd need to null check in the consumer.
see
https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Mono.html#doOnNext-java.util.function.Consumer-

https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Mono.html#doOnSuccess-java.util.function.Consumer-

[kasobol-msft]

Test	Arguments	1.30.0	source	%Change
jsonsend	--size 10 --parallel 64 --backend-type blobs --warmup 15 --duration 15	10809.14	13017.89	20.43%
jsonsend	--size 1000 --parallel 64 --backend-type blobs --warmup 15 --duration 15	13067.39	12907.40	-1.22%
jsonreceive	--size 10 --parallel 64 --backend-type blobs --warmup 15 --duration 15	25888.90	25900.12	0.04%
jsonreceive	--size 1000 --parallel 64 --backend-type blobs --warmup 15 --duration 15	24803.62	24613.67	-0.77%
xmlsend	--size 10 --parallel 64 --backend-type blobs --warmup 15 --duration 15	12979.08	13008.76	0.23%
xmlsend	--size 1000 --parallel 64 --backend-type blobs --warmup 15 --duration 15	12987.90	12897.35	-0.70%
xmlreceive	--size 10 --parallel 64 --backend-type blobs --warmup 15 --duration 15	25610.82	25652.50	0.16%
xmlreceive	--size 1000 --parallel 64 --backend-type blobs --warmup 15 --duration 15	22679.80	22560.85	-0.52%
binarydatasend	--size 10240 --binary-data-source bytes --parallel 16 --backend-type blobs --warmup 15 --duration 15	3511.92	3483.51	-0.81%
binarydatasend	--size 10240 --binary-data-source file --parallel 16 --backend-type blobs --warmup 15 --duration 15	3475.10	3467.56	-0.22%
binarydatasend	--size 10240 --binary-data-source flux --parallel 16 --backend-type blobs --warmup 15 --duration 15	3535.32	3491.02	-1.25%
binarydatasend	--size 10240 --binary-data-source stream --parallel 16 --backend-type blobs --warmup 15 --duration 15	3459.40	3457.61	-0.05%
binarydatasend	--size 10485760 --binary-data-source bytes --parallel 8 --backend-type blobs --warmup 15 --duration 15	81.08	80.11	-1.20%
binarydatasend	--size 10485760 --binary-data-source file --parallel 8 --backend-type blobs --warmup 15 --duration 15	105.30	104.76	-0.51%
binarydatasend	--size 10485760 --binary-data-source flux --parallel 8 --backend-type blobs --warmup 15 --duration 15	85.41	84.63	-0.91%
binarydatasend	--size 10485760 --binary-data-source stream --parallel 8 --backend-type blobs --warmup 15 --duration 15	107.54	107.99	0.42%
binarydatasend	--size 10240 --binary-data-source bytes --parallel 16 --backend-type blobs --http-client okhttp --warmup 15 --duration 15	323.99	3497.93	979.63%
binarydatasend	--size 10240 --binary-data-source file --parallel 16 --backend-type blobs --http-client okhttp --warmup 15 --duration 15	317.47	3476.57	995.09%
binarydatasend	--size 10240 --binary-data-source flux --parallel 16 --backend-type blobs --http-client okhttp --warmup 15 --duration 15	317.97	3457.69	987.43%
binarydatasend	--size 10240 --binary-data-source stream --parallel 16 --backend-type blobs --http-client okhttp --warmup 15 --duration 15	320.68	3484.87	986.70%
binarydatasend	--size 10485760 --binary-data-source bytes --parallel 8 --backend-type blobs --http-client okhttp --warmup 15 --duration 15	37.11	65.96	77.74%
binarydatasend	--size 10485760 --binary-data-source file --parallel 8 --backend-type blobs --http-client okhttp --warmup 15 --duration 15	40.04	64.60	61.34%
binarydatasend	--size 10485760 --binary-data-source flux --parallel 8 --backend-type blobs --http-client okhttp --warmup 15 --duration 15	39.07	65.14	66.75%
binarydatasend	--size 10485760 --binary-data-source stream --parallel 8 --backend-type blobs --http-client okhttp --warmup 15 --duration 15	39.14	69.91	78.64%
binarydatareceive	--size 10240 --parallel 16 --backend-type blobs --warmup 15 --duration 15	6637.52	6596.31	-0.62%
binarydatareceive	--size 10485760 --parallel 8 --backend-type blobs --warmup 15 --duration 15	105.87	107.03	1.10%
binarydatareceive	--size 10240 --parallel 16 --backend-type blobs --http-client okhttp --warmup 15 --duration 15	6462.88	6479.88	0.26%
binarydatareceive	--size 10485760 --parallel 8 --backend-type blobs --http-client okhttp --warmup 15 --duration 15	39.48	38.94	-1.35%