svn merge -c 1401309 FIXES: HDFS-4090. getFileChecksum() result incompatible when called against zero-byte files. (Kihwal Lee via daryn)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1401315 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -1616,6 +1616,9 @@ Release 0.23.5 - UNRELEASED
     HDFS-3224. Bug in check for DN re-registration with different storage ID
     (jlowe)
 
+    HDFS-4090. getFileChecksum() result incompatible when called against
+    zero-byte files. (Kihwal Lee via daryn)
+
 Release 0.23.4 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSClient.java

@@ -1795,6 +1795,13 @@ public class DFSClient implements java.io.Closeable {
         return new MD5MD5CRC32CastagnoliFileChecksum(bytesPerCRC,
             crcPerBlock, fileMD5);
       default:
+        // If there is no block allocated for the file,
+        // return one with the magic entry that matches what previous
+        // hdfs versions return.
+        if (locatedblocks.size() == 0) {
+          return new MD5MD5CRC32GzipFileChecksum(0, 0, fileMD5);
+        }
+
         // we should never get here since the validity was checked
         // when getCrcType() was called above.
         return null;

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDistributedFileSystem.java

@@ -515,6 +515,21 @@ public class TestDistributedFileSystem {
       final FileChecksum webhdfs_qfoocs = webhdfs.getFileChecksum(webhdfsqualified);
       System.out.println("webhdfs_qfoocs=" + webhdfs_qfoocs);
 
+      //create a zero byte file
+      final Path zeroByteFile = new Path(dir, "zeroByteFile" + n);
+      {
+        final FSDataOutputStream out = hdfs.create(zeroByteFile, false, buffer_size,
+            (short)2, block_size);
+        out.close();
+      }
+
+      // verify the magic val for zero byte files
+      {
+        final FileChecksum zeroChecksum = hdfs.getFileChecksum(zeroByteFile);
+        assertEquals(zeroChecksum.toString(),
+            "MD5-of-0MD5-of-0CRC32:70bc8f4b72a86921468bf8e8441dce51");
+      }
+
       //write another file
       final Path bar = new Path(dir, "bar" + n);
       {