truncate new segment files before use: LUCENE-415

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@415808 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -48,6 +48,10 @@ Bug fixes
  8. LUCENE-607: ParallelReader's TermEnum fails to advance properly to
     new fields (Chuck Williams, Christian Kohlschuetter via Yonik Seeley)
 
+ 9. LUCENE-415: A previously unclean shutdown during indexing can cause
+    a non-empty segment file to be re-used, causing index corruption.
+    (Andy Hind via Yonik Seeley)
+        
 Optimizations
 
   1. LUCENE-586: TermDocs.skipTo() is now more efficient for multi-segment

src/java/org/apache/lucene/store/FSDirectory.java

@@ -496,6 +496,13 @@ class FSIndexOutput extends BufferedIndexOutput {
 
   public FSIndexOutput(File path) throws IOException {
     file = new RandomAccessFile(path, "rw");
+    if (file.length() == 0) {
+      // This can happen if there was a previous crash / unclean shutdown that
+      // left files around, then we end up re-using a segment name.
+      // If we have a logging framework in the future, a warning here might be
+      // a good idea.
+      file.setLength(0);
+    }
   }
 
   /** output methods: */