Fix docker push errors not failing build

src/functTest/groovy/com/bmuschko/gradle/docker/tasks/image/DockerPushImageFunctionalTest.groovy

@@ -0,0 +1,40 @@
+package com.bmuschko.gradle.docker.tasks.image
+
+import com.bmuschko.gradle.docker.AbstractGroovyDslFunctionalTest
+import org.gradle.testkit.runner.BuildResult
+
+class DockerPushImageFunctionalTest extends AbstractGroovyDslFunctionalTest {
+
+    def "fails on push error"() {
+        def image = createUniqueImageId()
+
+        buildFile << """
+            import com.bmuschko.gradle.docker.tasks.image.Dockerfile
+            import com.bmuschko.gradle.docker.tasks.image.DockerBuildImage
+            import com.bmuschko.gradle.docker.tasks.image.DockerPushImage
+
+            task dockerfile(type: Dockerfile) {
+                from '$TEST_IMAGE_WITH_TAG'
+                label(['maintainer': '[email protected]'])
+            }
+
+            task buildImage(type: DockerBuildImage) {
+                dependsOn dockerfile
+                inputDir = file("build/docker")
+                images.add("${image}")
+            }
+
+            task pushImage(type: DockerPushImage) {
+                dependsOn buildImage
+                images.add("${image}")
+            }
+        """
+
+        when:
+        BuildResult result = build('pushImage')
+
+        then:
+        def e = thrown(Exception)
+        e.message.contains("Could not push image")
+    }
+}

src/main/java/com/bmuschko/gradle/docker/tasks/image/DockerPushImage.java

@@ -20,13 +20,16 @@
 import com.bmuschko.gradle.docker.tasks.RegistryCredentialsAware;
 import com.github.dockerjava.api.async.ResultCallback;
 import com.github.dockerjava.api.command.PushImageCmd;
+import com.github.dockerjava.api.exception.DockerClientException;
 import com.github.dockerjava.api.model.AuthConfig;
 import com.github.dockerjava.api.model.PushResponseItem;
 import org.gradle.api.Action;
 import org.gradle.api.GradleException;
 import org.gradle.api.provider.SetProperty;
 import org.gradle.api.tasks.Input;
 
+import javax.annotation.Nullable;
+
 public class DockerPushImage extends AbstractDockerRemoteApiTask implements RegistryCredentialsAware {
 
     /**
@@ -80,14 +83,30 @@ public void registryCredentials(Action<? super DockerRegistryCredentials> action
     }
 
     private ResultCallback.Adapter<PushResponseItem> createCallback(final Action nextHandler) {
+        // Workaround to manually handle error logic - see https://github.com/docker-java/docker-java/issues/2140
         return new ResultCallback.Adapter<PushResponseItem>() {
+            @Nullable
+            private PushResponseItem latestItem = null;
+
             @Override
             public void onNext(PushResponseItem item) {
+                this.latestItem = item;
+
                 if (nextHandler != null) {
                     nextHandler.execute(item);
                 }
             }
 
+            @Override
+            protected void throwFirstError() {
+                super.throwFirstError();
+
+                if (latestItem == null) {
+                    throw new DockerClientException("Could not push image");
+                } else if (latestItem.isErrorIndicated()) {
+                    throw new DockerClientException("Could not push image: " + latestItem.getError());
+                }
+            }
         };
     }
 }