REST Client @RestForm does not convert for List<T>

[krnhotwings]

Describe the bug

(Apologies for any incorrect terminology.) Normally when creating REST resources in quarkus, one can attach @RestForm or @FormParam to List<T> to indicate a repeated URL encoded form parameter, and this conversion will work as expected. For example:

@POST
public String test(@RestForm List<String> param) {
    // Do stuff with `param`

    return "Success"
}

However, the same does not appear to work when describing a REST Client method in the same manner. Invoking the client method will throw an exception (see below.) Additionally, @RestQuery seems to work on List<T> where @RestForm/@FormParam does not.

Expected behavior

I would think that the annotations should behave the same between RESTEasy and REST Client. This page states that the two share the same infrastructure, which I would think includes parameter converters unless I'm misunderstanding something.

There's also this page that describes how to use@RestForm in REST Clients, but I'm not sure if this snippet of examples indicates "here are some, but not a complete set of, examples that can be done with @RestForm" or if it means "these are the only types that @RestForm supports in REST Clients"

Actual behavior

Invoking the API throws an exception:

@RestClient EchoClient api;

public void test() {
    api.post(List.of("abc", "123"));
}

java.lang.IllegalStateException: Form element 'org.acme.EchoClient.post' could not be converted to 'String' for REST Client interface 'org.acme.EchoClient'. A proper implementation of 'jakarta.ws.rs.ext.ParamConverter' needs to be returned by a 'jakarta.ws.rs.ext.ParamConverterProvider' that is registered with the client via the @RegisterProvider annotation on the REST Client interface.
        at org.acme.EchoClient$$QuarkusRestClientInterface.post(Unknown Source)
        at org.acme.EchoClient$$CDIWrapper.post(Unknown Source)
        at org.acme.EchoClient$$CDIWrapper_ClientProxy.post(Unknown Source)
        at org.acme.GreetingResource.postTest(GreetingResource.java:27)
        at org.acme.GreetingResource$quarkusrestinvoker$postTest_1a7b3ae538024acc32395521f5fafc87a70ba54b.invoke(Unknown Source)
        at org.jboss.resteasy.reactive.server.handlers.InvocationHandler.handle(InvocationHandler.java:29)
        at io.quarkus.resteasy.reactive.server.runtime.QuarkusResteasyReactiveRequestContext.invokeHandler(QuarkusResteasyReactiveRequestContext.java:141)
        at org.jboss.resteasy.reactive.common.core.AbstractResteasyReactiveContext.run(AbstractResteasyReactiveContext.java:147)
        at io.quarkus.vertx.core.runtime.VertxCoreRecorder$14.runWith(VertxCoreRecorder.java:599)
        at org.jboss.threads.EnhancedQueueExecutor$Task.doRunWith(EnhancedQueueExecutor.java:2516)
        at org.jboss.threads.EnhancedQueueExecutor$Task.run(EnhancedQueueExecutor.java:2495)
        at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1521)
        at org.jboss.threads.DelegatingRunnable.run(DelegatingRunnable.java:11)
        at org.jboss.threads.ThreadLocalResettingRunnable.run(ThreadLocalResettingRunnable.java:11)
        at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
        at java.base/java.lang.Thread.run(Thread.java:1583)

How to Reproduce?

Demo repo here:
https://github.com/krnhotwings/rest-client-test

1. Follow README to start http echo server: podman run --rm -d -p 8001:8080 mendhak/http-https-echo:latest
2. Startup quarkus server: quarkus dev
3. curl "http://localhost:8080/hello/post Exception is thrown
4. curl "http://localhost:8080/hello/get Works.

Exception is thrown here:
https://github.com/krnhotwings/rest-client-test/blob/main/src/main/java/org/acme/EchoClient.java#L19-L20

List<T> works with @RestQuery:
https://github.com/krnhotwings/rest-client-test/blob/main/src/main/java/org/acme/EchoClient.java#L16-L17

Where the client is being invoked:
https://github.com/krnhotwings/rest-client-test/blob/main/src/main/java/org/acme/GreetingResource.java#L20-L28

Output of uname -a or ver

Linux 6.8.4-200.fc39.x86_64 #1 SMP PREEMPT_DYNAMIC Thu Apr 4 20:45:21 UTC 2024 x86_64 GNU/Linux

Output of java -version

openjdk version "21.0.2" 2024-01-16 OpenJDK Runtime Environment GraalVM CE 21.0.2+13.1 (build 21.0.2+13-jvmci-23.1-b30) OpenJDK 64-Bit Server VM GraalVM CE 21.0.2+13.1 (build 21.0.2+13-jvmci-23.1-b30, mixed mode, sharing)

Quarkus version or git rev

3.9.1

Build tool (ie. output of mvnw --version or gradlew --version)

Gradle 8.6 rev d55c486870a0dc6f6278f53d21381396d0741c6e

Additional information

No response

[quarkus-bot]

/cc @cescoffier (rest-client), @geoand (rest-client)

[krnhotwings]

@geoand Hi Georgios, I tested this just now on 3.10.0.CR1 and while the fix works for @RestForm/@FormParam method params (thank you,) the exception is still thrown when using a List inside a @BeanParam bean class. In hindsight, I should've tested for this scenario...

I assume this is still a bug related to the above changes? Do you need anything from me to test for this?

[geoand]

I assume this is still a bug related to the above changes? Do you need anything from me to test for this?

Yeah, definitely a bug, do you mind opening a new issue for it?

Thanks

[david-cabillic]

I tried @FormParam("files") List<File> files with 3.13.0 and I got the same issue : "could not be converted to 'String' for REST Client interface "

[Roland42]

I still have the problem with @FormParam List with 3.15.1 : "could not be converted to 'String' for REST Client interface "

This issue does not seem to be fixed