Multipart download in REST Client Reactive

docs/src/main/asciidoc/rest-client-reactive.adoc

@@ -450,7 +450,7 @@ public interface ExtensionsService {
     // ...
 
     @GET
-    Uni<Set<Extension>> getByIdAsUni(@QueryParam("id") String id)
+    Uni<Set<Extension>> getByIdAsUni(@QueryParam("id") String id);
 }
 ----
 
@@ -470,7 +470,7 @@ import java.util.Set;
 import java.util.concurrent.CompletionStage;
 
 @Path("/extension")
-public class ExtensionsResource
+public class ExtensionsResource {
 
     @RestClient
     ExtensionsService extensionsService;
@@ -654,15 +654,19 @@ org.eclipse.microprofile.rest.client.propagateHeaders=Authorization,Proxy-Author
 
 == Multipart Form support
 
-Rest Client Reactive allows sending data as multipart forms. This way you can for example
+REST Client Reactive support multipart messages.
+
+=== Sending Multipart messages
+
+REST Client Reactive allows sending data as multipart forms. This way you can for example
 send files efficiently.
 
 To send data as a multipart form, you need to create a class that would encapsulate all the fields
 to be sent, e.g.
 
 [source, java]
 ----
-class FormDto {
+public class FormDto {
     @FormParam("file")
     @PartType(MediaType.APPLICATION_OCTET_STREAM)
     public File file;
@@ -697,6 +701,42 @@ by specifying `quarkus.rest-client.multipart-post-encoder-mode` in your
 clients created with the `@RegisterRestClient` annotation.
 All the available modes are described in the link:https://netty.io/4.1/api/io/netty/handler/codec/http/multipart/HttpPostRequestEncoder.EncoderMode.html[Netty documentation]
 
+=== Receiving Multipart Messages
+REST Client Reactive also supports receiving multipart messages.
+As with sending, to parse a multipart response, you need to create a class that describes the response data, e.g.
+
+[source,java]
+----
+public class FormDto {
+    @RestForm // <1>
+    @PartType(MediaType.APPLICATION_OCTET_STREAM)
+    public File file;
+
+    @FormParam("otherField") // <2>
+    @PartType(MediaType.TEXT_PLAIN)
+    public String textProperty;
+}
+----
+<1> uses the shorthand `@RestForm` annotation to make a field as a part of a multipart form
+<2> the standard `@FormParam` can also be used. It allows to override the name of the multipart part.
+
+Then, create an interface method that corresponds to the call and make it return the `FormDto`:
+[source,java]
+----
+    @GET
+    @Produces(MediaType.MULTIPART_FORM_DATA)
+    @Path("/get-file")
+    FormDto data sendMultipart();
+----
+
+At the moment, multipart response support is subject to the following limitations:
+
+- files sent in multipart responses can only be parsed to `File`, `Path` and `FileDownload`
+- each field of the response type has to be annotated with `@PartType` - fields without this annotation are ignored
+
+REST Client Reactive needs to know the classes used as multipart return types upfront. If you have an interface method that produces `multipart/form-data`, the return type will be discovered automatically. However, if you intend to use the `ClientBuilder` API to parse a response as multipart, you need to annotate your DTO class with `@MultipartForm`.
+
+WARNING: The files you download are not automatically removed and can take up a lot of disk space. Consider removing the files when you are done working with them.
 
 == Proxy support
 REST Client Reactive supports sending requests through a proxy.

extensions/resteasy-reactive/jaxrs-client-reactive/runtime/src/main/java/io/quarkus/jaxrs/client/reactive/runtime/JaxrsClientReactiveClientContextResolver.java

@@ -1,11 +1,13 @@
 package io.quarkus.jaxrs.client.reactive.runtime;
 
+import java.util.Map;
 import java.util.function.Supplier;
 
 import org.jboss.resteasy.reactive.client.impl.ClientProxies;
 import org.jboss.resteasy.reactive.client.impl.DefaultClientContext;
 import org.jboss.resteasy.reactive.client.spi.ClientContext;
 import org.jboss.resteasy.reactive.client.spi.ClientContextResolver;
+import org.jboss.resteasy.reactive.client.spi.MultipartResponseData;
 import org.jboss.resteasy.reactive.common.core.GenericTypeMapping;
 import org.jboss.resteasy.reactive.common.core.Serialisers;
 
@@ -51,6 +53,14 @@ public ClientProxies getClientProxies() {
                 }
                 return clientProxies;
             }
+
+            @Override
+            public Map<Class<?>, MultipartResponseData> getMultipartResponsesData() {
+                Map<Class<?>, MultipartResponseData> result = JaxrsClientReactiveRecorder.getMultipartResponsesData();
+                return result == null
+                        ? DefaultClientContext.INSTANCE.getMultipartResponsesData()
+                        : result;
+            }
         };
     }
 }

extensions/resteasy-reactive/jaxrs-client-reactive/runtime/src/main/java/io/quarkus/jaxrs/client/reactive/runtime/JaxrsClientReactiveRecorder.java

@@ -12,6 +12,7 @@
 
 import org.jboss.resteasy.reactive.client.impl.ClientProxies;
 import org.jboss.resteasy.reactive.client.impl.ClientSerialisers;
+import org.jboss.resteasy.reactive.client.spi.MultipartResponseData;
 import org.jboss.resteasy.reactive.common.core.GenericTypeMapping;
 import org.jboss.resteasy.reactive.common.core.Serialisers;
 
@@ -24,6 +25,7 @@ public class JaxrsClientReactiveRecorder extends ResteasyReactiveCommonRecorder
 
     private static volatile Serialisers serialisers;
     private static volatile GenericTypeMapping genericTypeMapping;
+    private static volatile Map<Class<?>, MultipartResponseData> multipartResponsesData;
 
     private static volatile ClientProxies clientProxies = new ClientProxies(Collections.emptyMap(), Collections.emptyMap());
 
@@ -39,6 +41,19 @@ public static GenericTypeMapping getGenericTypeMapping() {
         return genericTypeMapping;
     }
 
+    public static Map<Class<?>, MultipartResponseData> getMultipartResponsesData() {
+        return multipartResponsesData;
+    }
+
+    public void setMultipartResponsesData(Map<String, RuntimeValue<MultipartResponseData>> multipartResponsesData) {
+        Map<Class<?>, MultipartResponseData> runtimeMap = new HashMap<>();
+        for (Map.Entry<String, RuntimeValue<MultipartResponseData>> multipartData : multipartResponsesData.entrySet()) {
+            runtimeMap.put(loadClass(multipartData.getKey()), multipartData.getValue().getValue());
+        }
+
+        JaxrsClientReactiveRecorder.multipartResponsesData = runtimeMap;
+    }
+
     public void setupClientProxies(
             Map<String, RuntimeValue<BiFunction<WebTarget, List<ParamConverterProvider>, ?>>> clientImplementations,
             Map<String, String> failures) {

extensions/resteasy-reactive/jaxrs-client-reactive/runtime/src/main/java/io/quarkus/jaxrs/client/reactive/runtime/impl/MultipartResponseDataBase.java

@@ -0,0 +1,22 @@
+package io.quarkus.jaxrs.client.reactive.runtime.impl;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.jboss.resteasy.reactive.client.spi.FieldFiller;
+import org.jboss.resteasy.reactive.client.spi.MultipartResponseData;
+
+public abstract class MultipartResponseDataBase implements MultipartResponseData {
+
+    private final List<FieldFiller> fillers = new ArrayList<>();
+
+    @Override
+    public List<FieldFiller> getFieldFillers() {
+        return fillers;
+    }
+
+    @SuppressWarnings("unused") // used in generated classes
+    public void addFiller(FieldFiller filler) {
+        fillers.add(filler);
+    }
+}