Add the ability to specify an image's platform.

core/src/main/java/org/testcontainers/images/builder/ImageFromDockerfile.java

@@ -32,9 +32,11 @@
 import java.nio.file.Path;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
+import java.util.function.Consumer;
 import java.util.zip.GZIPOutputStream;
 
 @Slf4j
@@ -62,6 +64,8 @@ public class ImageFromDockerfile
 
     private Optional<String> target = Optional.empty();
 
+    private final Set<Consumer<BuildImageCmd>> buildImageCmdModifiers = new LinkedHashSet<>();
+
     private Set<String> dependencyImageNames = Collections.emptySet();
 
     public ImageFromDockerfile() {
@@ -180,6 +184,7 @@ protected void configure(BuildImageCmd buildImageCmd) {
 
         this.buildArgs.forEach(buildImageCmd::withBuildArg);
         this.target.ifPresent(buildImageCmd::withTarget);
+        this.buildImageCmdModifiers.forEach(hook -> hook.accept(buildImageCmd));
     }
 
     private void prePullDependencyImages(Set<String> imagesToPull) {
@@ -248,4 +253,16 @@ public ImageFromDockerfile withDockerfile(Path dockerfile) {
         this.dockerfile = Optional.of(dockerfile);
         return this;
     }
+
+    /**
+     * Allow low level modifications of {@link BuildImageCmd}.
+     * Warning: this does expose the underlying docker-java API so might change outside of our control.
+     *
+     * @param modifier {@link Consumer} of {@link BuildImageCmd}.
+     * @return this
+     */
+    public ImageFromDockerfile withBuildImageCmdModifier(Consumer<BuildImageCmd> modifier) {
+        this.buildImageCmdModifiers.add(modifier);
+        return this;
+    }
 }

core/src/test/java/org/testcontainers/containers/MultiStageBuildTest.java

@@ -25,4 +25,20 @@ public void testDockerMultistageBuild() throws IOException, InterruptedException
             assertThat(container.execInContainer("ls").getStdout()).contains("hello.txt");
         }
     }
+
+    @Test
+    public void shouldBuildMultistageBuildWithBuildImageCmdModifier() throws IOException, InterruptedException {
+        try (
+            GenericContainer<?> container = new GenericContainer<>(
+                new ImageFromDockerfile()
+                    .withDockerfile(Paths.get("src/test/resources/Dockerfile-multistage"))
+                    .withBuildImageCmdModifier(cmd -> cmd.withTarget("builder"))
+            )
+                .withCommand("/bin/sh", "-c", "sleep 10")
+        ) {
+            container.start();
+            assertThat(container.execInContainer("pwd").getStdout()).contains("/my-files");
+            assertThat(container.execInContainer("ls").getStdout()).contains("hello.txt");
+        }
+    }
 }