improve performance when reading non zip64 zip files, merge from commons compress, based on patch by Robin Power

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@1439044 13f79535-47bb-0310-9956-ffa450edef68

CONTRIBUTORS

@@ -298,6 +298,7 @@ Robert Streich
 Robert Watkins
 Roberto Scaramuzzi
 Robin Green
+Robin Power
 Robin Verduijn
 Rob Oxspring
 Rob van Oostrum

contributors.xml

@@ -1201,6 +1201,10 @@
     <first>Robin</first>
     <last>Green</last>
   </name>
+  <name>
+    <first>Robin</first>
+    <last>Power</last>
+  </name>
   <name>
     <first>Robin</first>
     <last>Verduijn</last>

src/main/org/apache/tools/zip/ZipFile.java

@@ -666,12 +666,14 @@ public class ZipFile {
      */
     private void positionAtCentralDirectory()
         throws IOException {
-        boolean found = tryToLocateSignature(MIN_EOCD_SIZE + ZIP64_EOCDL_LENGTH,
-                                             MAX_EOCD_SIZE + ZIP64_EOCDL_LENGTH,
-                                             ZipOutputStream
-                                             .ZIP64_EOCD_LOC_SIG);
+        positionAtEndOfCentralDirectoryRecord();
+        archive.seek(archive.getFilePointer() - ZIP64_EOCDL_LENGTH);
+        archive.readFully(WORD_BUF);
+        boolean found = Arrays.equals(ZipOutputStream.ZIP64_EOCD_LOC_SIG,
+                                      WORD_BUF);
         if (!found) {
             // not a ZIP64 archive
+            skipBytes(ZIP64_EOCDL_LENGTH - WORD);
             positionAtCentralDirectory32();
         } else {
             positionAtCentralDirectory64();
@@ -686,7 +688,8 @@ public class ZipFile {
      */
     private void positionAtCentralDirectory64()
         throws IOException {
-        skipBytes(ZIP64_EOCDL_LOCATOR_OFFSET);
+        skipBytes(ZIP64_EOCDL_LOCATOR_OFFSET
+                  - WORD /* signature has already been read */);
         archive.readFully(DWORD_BUF);
         archive.seek(ZipEightByteInteger.getLongValue(DWORD_BUF));
         archive.readFully(WORD_BUF);
@@ -706,15 +709,23 @@ public class ZipFile {
      * record.
      */
     private void positionAtCentralDirectory32()
+        throws IOException {
+        skipBytes(CFD_LOCATOR_OFFSET);
+        archive.readFully(WORD_BUF);
+        archive.seek(ZipLong.getValue(WORD_BUF));
+    }
+
+    /**
+     * Searches for the and positions the stream at the start of the
+     * "End of central dir record".
+     */
+    private void positionAtEndOfCentralDirectoryRecord()
         throws IOException {
         boolean found = tryToLocateSignature(MIN_EOCD_SIZE, MAX_EOCD_SIZE,
                                              ZipOutputStream.EOCD_SIG);
         if (!found) {
             throw new ZipException("archive is not a ZIP archive");
         }
-        skipBytes(CFD_LOCATOR_OFFSET);
-        archive.readFully(WORD_BUF);
-        archive.seek(ZipLong.getValue(WORD_BUF));
     }
 
     /**