Allow setting external URL explicitly

build.gradle

@@ -58,6 +58,8 @@ dependencies {
 
     testImplementation libs.testcontainers.junit.jupiter
 
+    testImplementation libs.assertj
+
     testImplementation libs.gcs
     testRuntimeOnly libs.slf4j.log4j12
 }

settings.gradle

@@ -28,6 +28,8 @@ dependencyResolutionManagement {
             library('junit-jupiter-engine', 'org.junit.jupiter', 'junit-jupiter-engine').versionRef('junit')
             library('junit-jupiter-params', 'org.junit.jupiter', 'junit-jupiter-params').versionRef('junit')
 
+            library('assertj', 'org.assertj:assertj-core:3.24.2')
+
             library('slf4j-log4j12', 'org.slf4j:slf4j-log4j12:1.7.36')
 
             library('gcs', 'com.google.cloud:google-cloud-storage:2.26.1')

src/main/java/io/aiven/testcontainers/fakegcsserver/FakeGcsServerContainer.java

@@ -21,18 +21,21 @@
 import java.net.http.HttpClient;
 import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
+import java.util.Objects;
 
 import org.testcontainers.containers.GenericContainer;
 import org.testcontainers.utility.DockerImageName;
 
 public class FakeGcsServerContainer extends GenericContainer<FakeGcsServerContainer> {
-    private static final int PORT = 4443;
+    public static final int PORT = 4443;
 
     public static final String DEFAULT_VERSION = "1.47.4";
 
     public static final DockerImageName DEFAULT_IMAGE_NAME =
         DockerImageName.parse("fsouza/fake-gcs-server:" + DEFAULT_VERSION);
 
+    private String externalUrl = null;
+
     public FakeGcsServerContainer() {
         this(DEFAULT_IMAGE_NAME);
     }
@@ -47,20 +50,37 @@ public FakeGcsServerContainer(final DockerImageName dockerImageName) {
         addExposedPorts(PORT);
     }
 
+    public FakeGcsServerContainer withExternalURL(final String externalUrl) {
+        this.externalUrl = externalUrl;
+        return this;
+    }
+
     @Override
     public void start() {
         super.start();
         updateExternalUrl();
     }
 
+    /**
+     * The URL based on the host name and mapped port.
+     */
     public String url() {
         return "http://" + getHost() + ":" + getMappedPort(PORT);
     }
 
+    /**
+     * The URL based on the defined external URL.
+     *
+     * <p>Defaults to {@link FakeGcsServerContainer#url()}.
+     */
+    public String externalUrl() {
+        return Objects.requireNonNullElseGet(externalUrl, this::url);
+    }
+
     private void updateExternalUrl() {
         final String modifyExternalUrlRequestUri = url() + "/_internal/config";
         final String updateExternalUrlJson = "{"
-            + "\"externalUrl\": \"" + url() + "\""
+            + "\"externalUrl\": \"" + externalUrl() + "\""
             + "}";
 
         final HttpRequest req = HttpRequest.newBuilder()

src/test/java/io/aiven/testcontainers/fakegcsserver/FakeGcsServerContainerTest.java

@@ -24,11 +24,14 @@
 import com.google.cloud.storage.Storage;
 import com.google.cloud.storage.StorageOptions;
 import org.junit.jupiter.api.Named;
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
 import org.testcontainers.utility.DockerImageName;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 public class FakeGcsServerContainerTest {
     static final BucketInfo TEST_BUCKET = BucketInfo.of("test-bucket");
 
@@ -60,4 +63,21 @@ private static Stream<Arguments> provideTestParams() {
                     new FakeGcsServerContainer(DockerImageName.parse("fsouza/fake-gcs-server:1.47.3"))))
         );
     }
+
+    @Test
+    void testExternalUrlNotSet() {
+        try (final var fakeGcsServerContainer = new FakeGcsServerContainer()) {
+            fakeGcsServerContainer.start();
+            assertThat(fakeGcsServerContainer.externalUrl()).isEqualTo(fakeGcsServerContainer.url());
+        }
+    }
+
+    @Test
+    void testExternalUrlSet() {
+        try (final var fakeGcsServerContainer = new FakeGcsServerContainer().withExternalURL("http://aaa:1234")) {
+            fakeGcsServerContainer.start();
+            assertThat(fakeGcsServerContainer.externalUrl()).isEqualTo("http://aaa:1234");
+            assertThat(fakeGcsServerContainer.externalUrl()).isNotEqualTo(fakeGcsServerContainer.url());
+        }
+    }
 }