Multipart form data can no longer be sent with syncBody in WebTestClient [SPR-16131]

[spring-projects-issues]

Andy Wilkinson opened SPR-16131 and commented

I just upgraded to Framework 5.0.1 and noticed a regression when using syncBody to send multipart form data. With 5.0.0, this worked:

MultiValueMap<String, Object> multipartData = new LinkedMultiValueMap<>();
multipartData.add("file", new ByteArrayResource(new byte[] { 1, 2, 3, 4 }) {

	@Override
	public String getFilename() {
		return "image.png";
	}

});
ExchangeResult result = WebTestClient
		.bindToRouterFunction(RouterFunctions.route(POST("/foo"), (req) -> {
			req.body(BodyExtractors.toMultipartData()).block();
			return ServerResponse.ok().build();
		})).configureClient().baseUrl("http://localhost").build().post()
		.uri("/foo").syncBody(multipartData).exchange().expectBody()
		.returnResult();

Following the upgrade to 5.0.1 it appears to be trying to send form data rather than multipart data and, as a result, it fails:

java.lang.ClassCastException: org.springframework.restdocs.webtestclient.WebTestClientRequestConverterTests$1 cannot be cast to java.lang.String
	at org.springframework.http.codec.FormHttpMessageWriter.generateForm(FormHttpMessageWriter.java:127)
	at org.springframework.http.codec.FormHttpMessageWriter.lambda$write$0(FormHttpMessageWriter.java:102)
	at org.springframework.http.codec.FormHttpMessageWriter$$Lambda$185/198499365.apply(Unknown Source)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:107)
	at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:1649)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:156)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onSubscribe(MonoFlatMap.java:103)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:90)
	at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:54)
	at reactor.core.publisher.MonoMapFuseable.subscribe(MonoMapFuseable.java:59)
	at reactor.core.publisher.MonoFlatMap.subscribe(MonoFlatMap.java:60)
	at reactor.core.publisher.Mono.subscribe(Mono.java:2913)
	at reactor.core.publisher.Mono.subscribeWith(Mono.java:3021)
	at reactor.core.publisher.Mono.subscribe(Mono.java:2907)
	at reactor.core.publisher.Mono.subscribe(Mono.java:2874)
	at reactor.core.publisher.Mono.subscribe(Mono.java:2846)
	at org.springframework.test.web.reactive.server.HttpHandlerConnector.connect(HttpHandlerConnector.java:101)
	at org.springframework.test.web.reactive.server.WiretapConnector.connect(WiretapConnector.java:61)
	at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.exchange(ExchangeFunctions.java:74)
	at org.springframework.web.reactive.function.client.DefaultWebClient$DefaultRequestBodyUriSpec.exchange(DefaultWebClient.java:327)
	at org.springframework.test.web.reactive.server.DefaultWebTestClient$DefaultRequestBodyUriSpec.exchange(DefaultWebTestClient.java:282)
	at org.springframework.restdocs.webtestclient.WebTestClientRequestConverterTests.multipartUploadFromResource(WebTestClientRequestConverterTests.java:191)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
	at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
	Suppressed: java.lang.Exception: #block terminated with an error
		at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:126)
		at reactor.core.publisher.Mono.block(Mono.java:1185)
		... 25 more

It's trying to cast the anonymous ByteArrayResource subclass to a String. I can work around the problem by using .body(BodyInserters.fromMultipartData(multipartData)) in place of .syncBody(multipartData).

---

Affects: 5.0.1

Issue Links:

• WebClient failed to write application/x-www-form-urlencoded [SPR-16055] #20604 WebClient failed to write application/x-www-form-urlencoded
• Sending form and multipart data with WebTestClient [SPR-16118] #20666 Sending form and multipart data with WebTestClient

Referenced from: commits 8083eaa

[spring-projects-issues]

Rossen Stoyanchev commented

This seems to be related to the following change 9df6f3 which relaxed the constraint for FormHttpMessageWriter to work only with MultiValueMap declared with <String, String> generic types. So while it looks like a regression we actually have a design issue since both the Form~ and Multipart~ writer support MultiValueMap. By comparison FromHttpMessageConverter is a single class that supports writing both and in the write method checks the content of the map, so it doesn't depend on generics.

[spring-projects-issues]

Rossen Stoyanchev commented

Actually this is the commit 2962f0.

[spring-projects-issues]

Rossen Stoyanchev commented

This should be fixed now in master. See commit 8083ea for details.