Handling I/O errors from a rest client's methods

[pavelrappo]

I've been reading USING THE REST CLIENT and Rest Client for MicroProfile, but couldn't quickly find the answer to the following question. How do I know if a method of a rest client interface encounters an I/O error while sending a request?

There's one example in the specification that kind of suggests that I should declare IOException on the method, but I'm not sure. Also, various LLMs suggest that an instance of unchecked jakarta.ws.rs.ProcessingException is thrown with IOException as a cause somewhere in the exception chain. But for that in particular, I couldn't find any evidence in the specification.

Any tips on where I should be looking at?

[quarkus-bot[bot]]

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

[geoand]

If the error is encountered while sending the payload, you'll get a ProcessingException that wraps the IOException. See this

[pavelrappo]

Is it an implementation-specific detail or a specification requirement? Also, what about this method that throws IOException, from the specification example I linked to earlier? Do you know what the reason for declaring that exception is? Thanks!

@POST
@Path("upload/")
void uploadFile(List<EntityPart> entityParts) throws IOException;

[geoand]

I assume the later, but I can't say I remember

[pavelrappo]

@geoand, thanks; I asked microprofile/microprofile-rest-client#400.

Here's a relevant question. What should happen if a method of a rest client interface gets an HTTP-level error? How is it supposed to be signalled to the caller? The specification says that WebApplicationException should be thrown.

However, when I check an example built as per your guide, I get this exception:

org.jboss.resteasy.reactive.ClientWebApplicationException: Received: 'Not Found, status code 404' when invoking REST Client method: 'org.acme.rest.client.ExtensionsService#getById'
      at org.jboss.resteasy.reactive.client.impl.RestClientRequestContext.unwrapException(RestClientRequestContext.java:220)
      at org.jboss.resteasy.reactive.common.core.AbstractResteasyReactiveContext.handleException(AbstractResteasyReactiveContext.java:329)
      at org.jboss.resteasy.reactive.common.core.AbstractResteasyReactiveContext.run(AbstractResteasyReactiveContext.java:175)
      at io.smallrye.context.impl.wrappers.SlowContextualRunnable.run(SlowContextualRunnable.java:19)
      at org.jboss.resteasy.reactive.client.handlers.ClientSwitchToRequestContextRestHandler$1$1.handle(ClientSwitchToRequestContextRestHandler.java:38)
      at org.jboss.resteasy.reactive.client.handlers.ClientSwitchToRequestContextRestHandler$1$1.handle(ClientSwitchToRequestContextRestHandler.java:35)
      at io.vertx.core.impl.ContextInternal.dispatch(ContextInternal.java:270)
      at io.vertx.core.impl.ContextInternal.dispatch(ContextInternal.java:252)
      at io.vertx.core.impl.ContextInternal.lambda$runOnContext$0(ContextInternal.java:50)
      at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:173)
      at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:166)
      at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472)
      at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:566)
      at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:998)
      at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
      at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
      at java.base/java.lang.Thread.run(Thread.java:1583)
Caused by: jakarta.ws.rs.WebApplicationException: Not Found, status code 404
      at io.quarkus.rest.client.reactive.runtime.DefaultMicroprofileRestClientExceptionMapper.toThrowable(DefaultMicroprofileRestClientExceptionMapper.java:19)
      at io.quarkus.rest.client.reactive.runtime.MicroProfileRestClientResponseFilter.filter(MicroProfileRestClientResponseFilter.java:55)
      at org.jboss.resteasy.reactive.client.handlers.ClientResponseFilterRestHandler.handle(ClientResponseFilterRestHandler.java:21)
      at org.jboss.resteasy.reactive.client.handlers.ClientResponseFilterRestHandler.handle(ClientResponseFilterRestHandler.java:10)
      at org.jboss.resteasy.reactive.common.core.AbstractResteasyReactiveContext.invokeHandler(AbstractResteasyReactiveContext.java:231)
      at org.jboss.resteasy.reactive.common.core.AbstractResteasyReactiveContext.run(AbstractResteasyReactiveContext.java:147)
      ... 14 more

While WebApplicationException is present, it's an inner exception, not the outer one. The outer exception is some implementation-specific org.jboss.resteasy.reactive.ClientWebApplicationException.

[pavelrappo]

FWIW, if I set up a custom ResponseExceptionMapper, I will see its exceptions as outer exceptions.

For example, if I use this mapper, then I will see RuntimeException in the logs and nothing else, exactly as I would expect:

public class MyResponseExceptionMapper 
        implements ResponseExceptionMapper<RuntimeException> {

    @Override
    public RuntimeException toThrowable(Response response) {
        return new RuntimeException(String.valueOf(response.getStatus()));
    }
}

java.lang.RuntimeException: 404
	at org.acme.rest.client.MyResponseExceptionMapper.toThrowable(MyResponseExceptionMapper.java:11)
	at org.acme.rest.client.MyResponseExceptionMapper.toThrowable(MyResponseExceptionMapper.java:6)
	at io.quarkus.rest.client.reactive.runtime.MicroProfileRestClientResponseFilter.filter(MicroProfileRestClientResponseFilter.java:55)
	at org.jboss.resteasy.reactive.client.handlers.ClientResponseFilterRestHandler.handle(ClientResponseFilterRestHandler.java:21)
	at org.jboss.resteasy.reactive.client.handlers.ClientResponseFilterRestHandler.handle(ClientResponseFilterRestHandler.java:10)
	at org.jboss.resteasy.reactive.common.core.AbstractResteasyReactiveContext.invokeHandler(AbstractResteasyReactiveContext.java:231)
	at org.jboss.resteasy.reactive.common.core.AbstractResteasyReactiveContext.run(AbstractResteasyReactiveContext.java:147)
	at io.smallrye.context.impl.wrappers.SlowContextualRunnable.run(SlowContextualRunnable.java:19)
	at org.jboss.resteasy.reactive.client.handlers.ClientSwitchToRequestContextRestHandler$1$1.handle(ClientSwitchToRequestContextRestHandler.java:38)
	at org.jboss.resteasy.reactive.client.handlers.ClientSwitchToRequestContextRestHandler$1$1.handle(ClientSwitchToRequestContextRestHandler.java:35)
	at io.vertx.core.impl.ContextInternal.dispatch(ContextInternal.java:270)
	at io.vertx.core.impl.ContextInternal.dispatch(ContextInternal.java:252)
	at io.vertx.core.impl.ContextInternal.lambda$runOnContext$0(ContextInternal.java:50)
	at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:173)
	at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:166)
	at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472)
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:566)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:998)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.base/java.lang.Thread.run(Thread.java:1583)

[pavelrappo]

On my most recent question. Silly me! org.jboss.resteasy.reactive.ClientWebApplicationException is a subclass of jakarta.ws.rs.WebApplicationException. So no issue here. Sorry for the noise.