bugfix: prevent LzoDecompressor from entering endless loop when a emp…

…ty lzo file comes.

Signed-off-by: Todd Lipcon <todd@cloudera.com>

src/java/com/hadoop/compression/lzo/LzoDecompressor.java

@@ -296,21 +296,19 @@ public synchronized int decompress(byte[] b, int off, int len)
       }
 
       // Check if there is data to decompress
-      if (compressedDirectBufLen <= 0) {
-        return 0;
-      }
-
-      // Re-initialize the lzo's output direct-buffer
-      uncompressedDirectBuf.rewind();
-      uncompressedDirectBuf.limit(directBufferSize);
+      if (compressedDirectBufLen > 0) {
+        // Re-initialize the lzo's output direct-buffer
+        uncompressedDirectBuf.rewind();
+        uncompressedDirectBuf.limit(directBufferSize);
 
-      // Decompress data
-      numBytes = decompressBytesDirect(strategy.getDecompressor());
-      uncompressedDirectBuf.limit(numBytes);
+        // Decompress data
+        numBytes = decompressBytesDirect(strategy.getDecompressor());
+        uncompressedDirectBuf.limit(numBytes);
 
-      // Return atmost 'len' bytes
-      numBytes = Math.min(numBytes, len);
-      ((ByteBuffer)uncompressedDirectBuf).get(b, off, numBytes);
+        // Return atmost 'len' bytes
+        numBytes = Math.min(numBytes, len);
+        ((ByteBuffer)uncompressedDirectBuf).get(b, off, numBytes);
+      }
     }
 
     // Set 'finished' if lzo has consumed all user-data

src/test/com/hadoop/compression/lzo/TestLzopInputStream.java

@@ -43,6 +43,7 @@ public class TestLzopInputStream extends TestCase {
   private final String bigFile = "100000.txt";
   private final String mediumFile = "1000.txt";
   private final String smallFile = "100.txt";
+  private final String emptyFile = "0.txt";
 
   @Override
   protected void setUp() throws Exception {
@@ -81,6 +82,14 @@ public void testSmallFile() throws NoSuchAlgorithmException, IOException,
     runTest(smallFile);
   }
 
+  /**
+   * Test against a 0 line file.
+   */
+  public void testEmptyFile() throws NoSuchAlgorithmException, IOException,
+  InterruptedException {
+    runTest(emptyFile);
+  }
+
   /**
    * Test that reading an lzo-compressed file produces the same lines as reading the equivalent
    * flat file.  The test opens both the compressed and flat file, successively reading each