Properly implement ClientRequestContext#setEntity

This method can be called by filters to override
the entity being sent by the JAX-RS client and
before this commit we were not properly handling
the case where either the entity was set to null
or only the body of the entity was being set
(and not the media type).

Fixes: quarkusio#33738

extensions/resteasy-reactive/rest-client-reactive/deployment/src/test/java/io/quarkus/rest/client/reactive/provider/EntitySettingRequestFilterTest.java

@@ -0,0 +1,74 @@
+package io.quarkus.rest.client.reactive.provider;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.IOException;
+import java.net.URI;
+
+import jakarta.ws.rs.POST;
+import jakarta.ws.rs.Path;
+import jakarta.ws.rs.client.ClientRequestContext;
+import jakarta.ws.rs.client.ClientRequestFilter;
+
+import org.eclipse.microprofile.rest.client.RestClientBuilder;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.quarkus.test.QuarkusUnitTest;
+import io.quarkus.test.common.http.TestHTTPResource;
+
+public class EntitySettingRequestFilterTest {
+
+    @RegisterExtension
+    static final QuarkusUnitTest config = new QuarkusUnitTest()
+            .withApplicationRoot((jar) -> jar.addClasses(Resource.class, Client.class, EntityRequestFilter.class));
+
+    @TestHTTPResource
+    URI baseUri;
+
+    @Test
+    void testNullEntity() {
+        Client client = RestClientBuilder.newBuilder().baseUri(baseUri).register(new EntityRequestFilter(null))
+                .build(Client.class);
+        assertThat(client.call("ignored")).isEqualTo("null");
+    }
+
+    @Test
+    void testNonNullEntity() {
+        Client client = RestClientBuilder.newBuilder().baseUri(baseUri).register(new EntityRequestFilter("foo"))
+                .build(Client.class);
+        assertThat(client.call("ignored")).isEqualTo("foo");
+    }
+
+    @Path("/")
+    public static class Resource {
+        @POST
+        public String returnHeaders(String body) {
+            if ((body == null) || body.isEmpty()) {
+                return "null";
+            }
+            return body;
+        }
+    }
+
+    public interface Client {
+
+        @Path("/")
+        @POST
+        String call(String body);
+    }
+
+    public static class EntityRequestFilter implements ClientRequestFilter {
+
+        private final String entity;
+
+        public EntityRequestFilter(String entity) {
+            this.entity = entity;
+        }
+
+        @Override
+        public void filter(ClientRequestContext context) throws IOException {
+            context.setEntity(entity);
+        }
+    }
+}

independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientRequestContextImpl.java

@@ -171,8 +171,12 @@ public Locale getLanguage() {
 
     @Override
     public MediaType getMediaType() {
+        if (restClientRequestContext.entity == null) {
+            return null;
+        }
         // those come from the entity
-        return restClientRequestContext.entity != null ? restClientRequestContext.entity.getMediaType() : null;
+        return restClientRequestContext.entity.getMediaType() == RestClientRequestContext.IGNORED_MEDIA_TYPE ? null
+                : restClientRequestContext.entity.getMediaType();
     }
 
     @Override
@@ -515,12 +519,8 @@ private boolean isContentType(Object key) {
         }
 
         private String mediaType() {
-            Entity<?> entity = restClientRequestContext.entity;
-            return entity == null
-                    ? null
-                    : entity.getMediaType() == null
-                            ? null
-                            : entity.getMediaType().toString();
+            MediaType mediaType = getMediaType();
+            return mediaType == null ? null : mediaType.toString();
         }
     }
 }

independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/RestClientRequestContext.java

@@ -60,6 +60,8 @@ public class RestClientRequestContext extends AbstractResteasyReactiveContext<Re
     public static final String DEFAULT_CONTENT_TYPE_PROP = "io.quarkus.rest.client.defaultContentType";
     private static final String TMP_FILE_PATH_KEY = "tmp_file_path";
 
+    static final MediaType IGNORED_MEDIA_TYPE = new MediaType("ignored", "ignored");
+
     private final HttpClient httpClient;
     // Changeable by the request filter
     String httpMethod;
@@ -273,7 +275,14 @@ public Buffer writeEntity(Entity<?> entity, MultivaluedMap<String, String> heade
     }
 
     public void setEntity(Object entity, Annotation[] annotations, MediaType mediaType) {
-        this.entity = Entity.entity(entity, mediaType, annotations);
+        if (entity == null) {
+            this.entity = null;
+        } else {
+            if (mediaType == null) {
+                mediaType = IGNORED_MEDIA_TYPE; // we need this in order to avoid getting IAE from Variant...
+            }
+            this.entity = Entity.entity(entity, mediaType, annotations);
+        }
     }
 
     public CompletableFuture<ResponseImpl> getResult() {