Add support of docker multi stage builds

src/main/java/io/fabric8/maven/docker/service/BuildService.java

@@ -8,6 +8,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
+import java.util.LinkedList;
 
 import io.fabric8.maven.docker.access.BuildOptions;
 import io.fabric8.maven.docker.access.DockerAccess;
@@ -199,14 +200,20 @@ private void autoPullBaseImage(ImageConfiguration imageConfig, ImagePullManager
             return;
         }
 
-        String fromImage;
+        List<String> fromImages;
         if (buildConfig.isDockerFileMode()) {
-            fromImage = extractBaseFromDockerfile(buildConfig, buildContext);
+            fromImages = extractBaseFromDockerfile(buildConfig, buildContext);
         } else {
-            fromImage = extractBaseFromConfiguration(buildConfig);
+            fromImages = new LinkedList<>();
+            String baseImage = extractBaseFromConfiguration(buildConfig);
+            if (baseImage!=null) {
+                fromImages.add(extractBaseFromConfiguration(buildConfig));
+            }
         }
-        if (fromImage != null && !DockerAssemblyManager.SCRATCH_IMAGE.equals(fromImage)) {
-            registryService.pullImageWithPolicy(fromImage, imagePullManager, buildContext.getRegistryConfig(), queryService.hasImage(fromImage));
+        for (String fromImage : fromImages) {
+            if (fromImage != null && !DockerAssemblyManager.SCRATCH_IMAGE.equals(fromImage)) {
+                registryService.pullImageWithPolicy(fromImage, imagePullManager, buildContext.getRegistryConfig(), queryService.hasImage(fromImage));
+            }
         }
     }
 
@@ -222,17 +229,17 @@ private String extractBaseFromConfiguration(BuildImageConfiguration buildConfig)
         return fromImage;
     }
 
-    private String extractBaseFromDockerfile(BuildImageConfiguration buildConfig, BuildContext buildContext) {
-        String fromImage;
+    private List<String> extractBaseFromDockerfile(BuildImageConfiguration buildConfig, BuildContext buildContext) {
+        List<String> fromImage;
         try {
             File fullDockerFilePath = buildConfig.getAbsoluteDockerFilePath(buildContext.getMojoParameters());
-            fromImage = DockerFileUtil.extractBaseImage(
+            fromImage = DockerFileUtil.extractBaseImages(
                 fullDockerFilePath,
                 DockerFileUtil.createInterpolator(buildContext.getMojoParameters(), buildConfig.getFilter()));
         } catch (IOException e) {
             // Cant extract base image, so we wont try an auto pull. An error will occur later anyway when
             // building the image, so we are passive here.
-            fromImage = null;
+            return Collections.emptyList();
         }
         return fromImage;
     }

src/main/java/io/fabric8/maven/docker/util/DockerFileUtil.java

@@ -17,6 +17,7 @@
 
 import java.io.*;
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -43,16 +44,31 @@ private DockerFileUtil() {}
      *
      * @param dockerFile file from where to extract the base image
      * @param interpolator interpolator for replacing properties
+     * @deprecated Use {@link DockerFileUtil#extractBaseImages} extractBaseImages instead
      */
+    @Deprecated
     public static String extractBaseImage(File dockerFile, FixedStringSearchInterpolator interpolator) throws IOException {
+        List<String> result = extractBaseImages(dockerFile, interpolator);
+        return result.isEmpty() ? null : result.iterator().next();
+    }
+
+    /**
+     * Extract the base images from a dockerfile. All lines containing a <code>FROM</code> is
+     * taken.
+     *
+     * @param dockerFile file from where to extract the base image
+     * @param interpolator interpolator for replacing properties
+     * @return LinkedList of base images name or empty collection if none is found.
+     */
+    public static List<String> extractBaseImages(File dockerFile, FixedStringSearchInterpolator interpolator) throws IOException {
         List<String[]> fromLines = extractLines(dockerFile, "FROM", interpolator);
-        if (!fromLines.isEmpty()) {
-            String[] parts = fromLines.get(0);
-            if (parts.length > 1) {
-                return parts[1];
+        LinkedList<String> result = new LinkedList<>();
+        for (String[] fromLine :  fromLines) {
+            if (fromLine.length > 1) {
+                result.add(fromLine[1]);
             }
         }
-        return null;
+        return result;
     }
 
     /**

src/test/java/io/fabric8/maven/docker/util/DockerFileUtilTest.java

@@ -17,11 +17,7 @@
 
 import java.io.*;
 import java.nio.file.Files;
-import java.util.Collections;
-import java.util.Date;
-import java.util.HashMap;
-import java.util.Map;
-import java.util.Properties;
+import java.util.*;
 
 import org.apache.commons.io.FileUtils;
 import org.apache.maven.artifact.repository.ArtifactRepository;
@@ -52,6 +48,17 @@ public void testSimple() throws Exception {
             toTest, FixedStringSearchInterpolator.create()));
     }
 
+    @Test
+    public void testMultiStage() throws Exception {
+        File toTest = copyToTempDir("Dockerfile_multi_stage");
+        Iterator<String> fromClauses = DockerFileUtil.extractBaseImages(
+             toTest, FixedStringSearchInterpolator.create()).iterator();
+
+        assertEquals("fabric8/s2i-java", fromClauses.next());
+        assertEquals("fabric8/s1i-java", fromClauses.next());
+        assertEquals(false, fromClauses.hasNext());
+    }
+
     private File copyToTempDir(String resource) throws IOException {
         File dir = Files.createTempDirectory("d-m-p").toFile();
         File ret = new File(dir, "Dockerfile");

src/test/resources/io/fabric8/maven/docker/util/Dockerfile_multi_stage

@@ -0,0 +1,6 @@
+# Dockerfile with a multi FROM clause
+# see https://docs.docker.com/develop/develop-images/multistage-build/
+
+FROM fabric8/s2i-java
+
+FROM fabric8/s1i-java