fix failure message to mention version.bin instead of index.drd not e…

…xists msg (apache#4102)

api/src/main/java/io/druid/segment/SegmentUtils.java

@@ -40,9 +40,18 @@ public static int getVersionFromDir(File inDir) throws IOException
 
     final File indexFile = new File(inDir, "index.drd");
     int version;
-    try (InputStream in = new FileInputStream(indexFile)) {
-      version = in.read();
+    if (indexFile.exists()) {
+      try (InputStream in = new FileInputStream(indexFile)) {
+        version = in.read();
+      }
+      return version;
     }
-    return version;
+
+    throw new IOException(
+        String.format(
+            "Invalid segment dir [%s]. Can't find either of version.bin or index.drd.",
+            inDir
+        )
+    );
   }
 }

api/src/test/java/io/druid/segment/SegmentUtilsTest.java

@@ -0,0 +1,61 @@
+/*
+ * Licensed to Metamarkets Group Inc. (Metamarkets) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. Metamarkets licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package io.druid.segment;
+
+import com.google.common.primitives.Ints;
+import org.apache.commons.io.FileUtils;
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.File;
+import java.io.IOException;
+
+/**
+ */
+public class SegmentUtilsTest
+{
+  @Rule
+  public final TemporaryFolder tempFolder = new TemporaryFolder();
+
+  @Test
+  public void testVersionBin() throws Exception
+  {
+    File dir = tempFolder.newFolder();
+    byte[] bytes = Ints.toByteArray(9);
+    FileUtils.writeByteArrayToFile(new File(dir, "version.bin"), Ints.toByteArray(9));
+    Assert.assertEquals(9, SegmentUtils.getVersionFromDir(dir));
+  }
+
+  @Test
+  public void testIndexDrd() throws Exception
+  {
+    File dir = tempFolder.newFolder();
+    FileUtils.writeByteArrayToFile(new File(dir, "index.drd"), new byte[]{(byte) 0x8});
+    Assert.assertEquals(8, SegmentUtils.getVersionFromDir(dir));
+  }
+
+  @Test(expected = IOException.class)
+  public void testException() throws Exception
+  {
+    SegmentUtils.getVersionFromDir(tempFolder.newFolder());
+  }
+}