Add converter for ObjectId class.

This fixes legacy support for serializing an Objectid as a
byte array.

Author: kevinsawicki

src/main/java/hudson/plugins/git/GitSCM.java

@@ -1284,6 +1284,7 @@ public static final class DescriptorImpl extends SCMDescriptor<GitSCM> {
 
         public DescriptorImpl() {
             super(GitSCM.class, GitRepositoryBrowser.class);
+            Run.XSTREAM.registerConverter(new ObjectIdConverter());
             load();
         }
 

src/main/java/hudson/plugins/git/ObjectIdConverter.java

@@ -0,0 +1,49 @@
+package hudson.plugins.git;
+
+import com.thoughtworks.xstream.converters.Converter;
+import com.thoughtworks.xstream.converters.MarshallingContext;
+import com.thoughtworks.xstream.converters.UnmarshallingContext;
+import com.thoughtworks.xstream.core.util.Base64Encoder;
+import com.thoughtworks.xstream.io.HierarchicalStreamReader;
+import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
+
+import org.eclipse.jgit.lib.ObjectId;
+
+/**
+ * Object id converter. This is required for legacy support for originally
+ * serializing an ObjectId as a byte[]. The new format supports marshalling as a
+ * standard lower-case SHA1 hexadecimal string but unmarshalling both byte[] and
+ * String types.
+ */
+public class ObjectIdConverter implements Converter {
+
+    private Base64Encoder base64;
+
+    /**
+     * Create ObjectId converter
+     */
+    public ObjectIdConverter() {
+        base64 = new Base64Encoder();
+    }
+
+    public boolean canConvert(Class type) {
+        return ObjectId.class == type;
+    }
+
+    public void marshal(Object source, HierarchicalStreamWriter writer,
+            MarshallingContext context) {
+        writer.setValue(((ObjectId) source).name());
+    }
+
+    public Object unmarshal(HierarchicalStreamReader reader,
+            final UnmarshallingContext context) {
+        if (reader.hasMoreChildren()
+                && "byte-array".equals(reader.peekNextChild())) {
+            reader.moveDown();
+            ObjectId sha1 = ObjectId.fromRaw(base64.decode(reader.getValue()));
+            reader.moveUp();
+            return sha1;
+        } else
+            return ObjectId.fromString(reader.getValue());
+    }
+}