HADOOP-508. Fix a bug in FSDataInputStream where incorrect data was sometimes returned after seeking to a random location. Contributed by Milind.

git-svn-id: https://svn.apache.org/repos/asf/lucene/hadoop/trunk@450586 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -80,6 +80,10 @@ Trunk (unreleased changes)
     the FileSystem API, and use it in DFSShell ('bin/hadoop dfs')
     commands.  (Hairong Kuang via cutting)
 
+21. HADOOP-508.  Fix a bug in FSDataInputStream.  Incorrect data was
+    returned after seeking to a random location.
+    (Milind Bhandarkar via cutting)
+
 
 Release 0.6.2 (unreleased)
 

src/java/org/apache/hadoop/fs/FSDataInputStream.java

@@ -193,7 +193,8 @@ public class FSDataInputStream extends DataInputStream {
     public void seek(long desired) throws IOException {
       long end = ((PositionCache)in).getPos();
       long start = end - this.count;
-      if (desired >= start && desired < end) {
+      int avail = this.count - this.pos;
+      if (desired >= start && desired < end && avail > 0) {
         this.pos = (int)(desired - start);        // can position within buffer
       } else {
         this.count = 0;                           // invalidate buffer

src/test/org/apache/hadoop/dfs/TestSeekBug.java

@@ -0,0 +1,104 @@
+package org.apache.hadoop.dfs;
+
+import javax.swing.filechooser.FileSystemView;
+import junit.framework.TestCase;
+import java.io.*;
+import java.util.Random;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FSDataInputStream;
+import org.apache.hadoop.fs.FSInputStream;
+import org.apache.hadoop.fs.FSDataOutputStream;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+
+/**
+ * This class tests the presence of seek bug as described
+ * in HADOOP-508 
+ * @author Milind Bhandarkar
+ */
+public class TestSeekBug extends TestCase {
+  static final long seed = 0xDEADBEEFL;
+  static final int ONEMB = 1 << 20;
+  
+  private void writeFile(FileSystem fileSys, Path name) throws IOException {
+    // create and write a file that contains 1MB
+    DataOutputStream stm = fileSys.create(name);
+    byte[] buffer = new byte[ONEMB];
+    Random rand = new Random(seed);
+    rand.nextBytes(buffer);
+    stm.write(buffer);
+    stm.close();
+  }
+  
+  private void checkAndEraseData(byte[] actual, int from, byte[] expected, String message) {
+    for (int idx = 0; idx < actual.length; idx++) {
+      this.assertEquals(message+" byte "+(from+idx)+" differs. expected "+
+          expected[from+idx]+" actual "+actual[idx],
+          actual[idx], expected[from+idx]);
+      actual[idx] = 0;
+    }
+  }
+  
+  private void seekReadFile(FileSystem fileSys, Path name) throws IOException {
+    FSInputStream stmRaw = fileSys.openRaw(name);
+    FSDataInputStream stm = new FSDataInputStream(stmRaw, 4096);
+    byte[] expected = new byte[ONEMB];
+    Random rand = new Random(seed);
+    rand.nextBytes(expected);
+    
+    // First read 128 bytes to set count in BufferedInputStream
+    byte[] actual = new byte[128];
+    stm.read(actual, 0, actual.length);
+    // Now read a byte array that is bigger than the internal buffer
+    actual = new byte[100000];
+    stm.read(actual, 0, actual.length);
+    checkAndEraseData(actual, 128, expected, "First Read Test");
+    // now do a small seek, within the range that is already read
+    stm.seek(96036); // 4 byte seek
+    actual = new byte[128];
+    stm.read(actual, 0, actual.length);
+    checkAndEraseData(actual, 96036, expected, "Seek Bug");
+    // all done
+    stm.close();
+  }
+  
+  private void cleanupFile(FileSystem fileSys, Path name) throws IOException {
+    assertTrue(fileSys.exists(name));
+    fileSys.delete(name);
+    assertTrue(!fileSys.exists(name));
+  }
+  
+  /**
+   * Test if the seek bug exists in FSDataInputStream in DFS.
+   */
+  public void testSeekBugDFS() throws IOException {
+    Configuration conf = new Configuration();
+    MiniDFSCluster cluster = new MiniDFSCluster(65312, conf, false);
+    FileSystem fileSys = cluster.getFileSystem();
+    try {
+      Path file1 = new Path("seektest.dat");
+      writeFile(fileSys, file1);
+      seekReadFile(fileSys, file1);
+      cleanupFile(fileSys, file1);
+    } finally {
+      fileSys.close();
+      cluster.shutdown();
+    }
+  }
+  
+  /**
+   * Tests if the seek bug exists in FSDataInputStream in LocalFS.
+   */
+  public void testSeekBugLocalFS() throws IOException {
+    Configuration conf = new Configuration();
+    FileSystem fileSys = FileSystem.getNamed("local", conf);
+    try {
+      Path file1 = new Path("build/test/data", "seektest.dat");
+      writeFile(fileSys, file1);
+      seekReadFile(fileSys, file1);
+      cleanupFile(fileSys, file1);
+    } finally {
+      fileSys.close();
+    }
+  }
+}