Make sure that we can roundtrip from Yaml and back into Yaml.

Changes made:
1. Added custom Representer to control output
2. Added custom Represent implementations for IntOrString
and byte arrays.
3. Made sure that we never output tags for any of our data,
since in general Kubernetes doesn't use Yaml tags.
4. Made sure that we don't print null values in our Yaml.
5. Enforce that certain keys, such as apiVersion, that are
typically at the top of Kubernetes Yaml files, are outputted that
way..

Author: John Daniels

util/src/main/java/io/kubernetes/client/util/Yaml.java

@@ -19,15 +19,30 @@
 import java.io.IOException;
 import java.io.Reader;
 import java.io.StringReader;
-import java.util.*;
+import java.io.Writer;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
 import okio.ByteString;
 import org.apache.commons.lang3.tuple.MutablePair;
 import org.apache.commons.lang3.tuple.Pair;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import org.yaml.snakeyaml.DumperOptions;
 import org.yaml.snakeyaml.constructor.Constructor;
+import org.yaml.snakeyaml.introspector.Property;
+import org.yaml.snakeyaml.nodes.MappingNode;
 import org.yaml.snakeyaml.nodes.Node;
+import org.yaml.snakeyaml.nodes.NodeTuple;
 import org.yaml.snakeyaml.nodes.ScalarNode;
+import org.yaml.snakeyaml.nodes.Tag;
+import org.yaml.snakeyaml.representer.Represent;
+import org.yaml.snakeyaml.representer.Representer;
 
 public class Yaml {
   private static Map<String, Class<?>> classes = new HashMap<>();
@@ -259,6 +274,46 @@ public static List<Object> loadAll(Reader reader) throws IOException {
     return list;
   }
 
+  /**
+   * Takes an API object and returns a YAML String representing that object.
+   *
+   * @param object The API object to dump.
+   * @return A YAML String representing the API object.
+   */
+  public static String dump(Object object) {
+    return getSnakeYaml().dump(object);
+  }
+
+  /**
+   * Takes an API object and writes a YAML string representing that object to the writer.
+   *
+   * @param object The API object to dump
+   * @param writer The writer to write the YAML to.
+   */
+  public static void dump(Object object, Writer writer) {
+    getSnakeYaml().dump(object, writer);
+  }
+
+  /**
+   * Takes an Iterator of YAML API objects and returns a YAML string representing all of them
+   *
+   * @param data The list of YAML API objects
+   * @return A String representing the list of YAML API objects.
+   */
+  public static String dumpAll(Iterator<? extends Object> data) {
+    return getSnakeYaml().dumpAll(data);
+  }
+
+  /**
+   * Takes an Iterator of YAML API objects and writes a YAML String representing all of them.
+   *
+   * @param data The list of YAML API objects.
+   * @param output The writer to output the YAML String to.
+   */
+  public static void dumpAll(Iterator<? extends Object> data, Writer output) {
+    getSnakeYaml().dumpAll(data, output);
+  }
+
   /** Defines constructor logic for custom types in this library. */
   public static class CustomConstructor extends Constructor {
     @Override
@@ -285,9 +340,93 @@ private byte[] constructByteArray(ScalarNode node) {
     }
   }
 
+  public static class CustomRepresenter extends Representer {
+    public CustomRepresenter() {
+      this.setDefaultFlowStyle(DumperOptions.FlowStyle.BLOCK);
+      this.representers.put(IntOrString.class, new RepresentIntOrString());
+      this.representers.put(byte[].class, new RepresentByteArray());
+    }
+
+    private class RepresentIntOrString implements Represent {
+      @Override
+      public Node representData(Object data) {
+        IntOrString intOrString = (IntOrString) data;
+        if (intOrString.isInteger()) {
+          return CustomRepresenter.this.representData(intOrString.getIntValue());
+        } else {
+          return CustomRepresenter.this.representData(intOrString.getStrValue());
+        }
+      }
+    }
+
+    private class RepresentByteArray implements Represent {
+      @Override
+      public Node representData(Object data) {
+        String value = ByteString.of((byte[]) data).base64();
+        return representScalar(Tag.STR, value);
+      }
+    }
+
+    /**
+     * This returns the ordering of properties that by convention should appear at the beginning of
+     * a Yaml object in Kubernetes.
+     */
+    private int getPropertyPosition(String property) {
+      switch (property) {
+        case "apiVersion":
+          return 0;
+        case "kind":
+          return 1;
+        case "metadata":
+          return 2;
+        case "spec":
+          return 3;
+        case "type":
+          return 4;
+        default:
+          return Integer.MAX_VALUE;
+      }
+    }
+
+    @Override
+    protected MappingNode representJavaBean(Set<Property> properties, Object javaBean) {
+      MappingNode node = super.representJavaBean(properties, javaBean);
+      // Always set the tag to MAP so that SnakeYaml doesn't print out the class name as a tag.
+      node.setTag(Tag.MAP);
+      // Sort the output of our map so that we put certain keys, such as apiVersion, first.
+      Collections.sort(
+          node.getValue(),
+          new Comparator<NodeTuple>() {
+            @Override
+            public int compare(NodeTuple a, NodeTuple b) {
+              String nameA = ((ScalarNode) a.getKeyNode()).getValue();
+              String nameB = ((ScalarNode) b.getKeyNode()).getValue();
+              int intCompare =
+                  Integer.compare(getPropertyPosition(nameA), getPropertyPosition(nameB));
+              if (intCompare != 0) {
+                return intCompare;
+              } else {
+                return nameA.compareTo(nameB);
+              }
+            }
+          });
+      return node;
+    }
+
+    @Override
+    protected NodeTuple representJavaBeanProperty(
+        Object javaBean, Property property, Object propertyValue, Tag customTag) {
+      // returning null for a null property value means we won't output it in the Yaml
+      if (propertyValue == null) {
+        return null;
+      }
+      return super.representJavaBeanProperty(javaBean, property, propertyValue, customTag);
+    }
+  }
+
   /** @return An instantiated SnakeYaml Object. */
   public static org.yaml.snakeyaml.Yaml getSnakeYaml() {
-    return new org.yaml.snakeyaml.Yaml(new CustomConstructor());
+    return new org.yaml.snakeyaml.Yaml(new CustomConstructor(), new CustomRepresenter());
   }
 
   /**

util/src/test/java/io/kubernetes/client/util/YamlTest.java

@@ -15,12 +15,18 @@
 import static org.junit.Assert.*;
 
 import com.google.common.io.Resources;
-import io.kubernetes.client.models.*;
+import io.kubernetes.client.models.AppsV1beta1Deployment;
+import io.kubernetes.client.models.V1ObjectMeta;
+import io.kubernetes.client.models.V1Secret;
+import io.kubernetes.client.models.V1Service;
+import io.kubernetes.client.models.V1ServicePort;
 import java.io.File;
 import java.io.IOException;
 import java.io.StringReader;
 import java.lang.reflect.Method;
 import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Paths;
 import java.util.List;
 import org.junit.Test;
 
@@ -132,6 +138,10 @@ public void testLoadAllFile() throws Exception {
         throw new Exception("some thing wrong happened");
       }
     }
+    String result = Yaml.dumpAll(list.iterator());
+    String expected =
+        new String(Files.readAllBytes(Paths.get(TEST_YAML_FILE_PATH)), StandardCharsets.UTF_8);
+    assertEquals(expected, result);
   }
 
   @Test

util/src/test/resources/test.yaml

@@ -1,9 +1,9 @@
 apiVersion: v1
 kind: Service
 metadata:
-  name: mock
   labels:
     app: mock
+  name: mock
 spec:
   ports:
   - port: 99
@@ -27,20 +27,16 @@ spec:
       name: helloworld
     spec:
       containers:
-        - name: helloworld
-          image: gcr.io/hightowerlabs/helloworld:0.0.1
-          imagePullPolicy: Always
-          args:
-            - "-http=127.0.0.1:8080"
+      - args:
+        - -http=127.0.0.1:8080
+        image: gcr.io/hightowerlabs/helloworld:0.0.1
+        imagePullPolicy: Always
+        name: helloworld
 ---
 apiVersion: v1
 kind: Secret
-
 metadata:
   name: secret
-
 type: Opaque
-
 data:
   secret-data: aGVsbG8=
-