Don't change the local header offset in the Central Directory File Header when it is set in the ZIP64 Extended Info field

Author: ebourg

jsign-core/src/main/java/net/jsign/zip/CentralDirectoryFileHeader.java

@@ -198,9 +198,10 @@ public long getLocalHeaderOffset() {
     }
 
     public void setLocalHeaderOffset(long offset) {
-        if (offset > 0xFFFFFFFFL) {
+        if (offset > 0xFFFFFFFFL || localHeaderOffset == 0xFFFFFFFFL) {
             Zip64ExtendedInfoExtraField zip64ExtraField = (Zip64ExtendedInfoExtraField) extraFields.get(1);
             zip64ExtraField.localHeaderOffset = offset;
+            localHeaderOffset = 0xFFFFFFFFL;
         } else {
             localHeaderOffset = offset;
         }

jsign-core/src/test/java/net/jsign/zip/CentralDirectoryFileHeaderTest.java

@@ -73,4 +73,19 @@ public void testReadWrongRecord() throws Exception {
             assertEquals("message", "Invalid Central Directory File Header signature 0x4034b50", e.getMessage());
         }
     }
+
+    @Test
+    public void testLocalHeaderOffsetUpdate() throws Exception {
+        File file = new File("target/test-classes/minimal.zip");
+
+        try (SeekableByteChannel channel = Files.newByteChannel(file.toPath(), StandardOpenOption.READ)) {
+            channel.position(0x247B);
+
+            CentralDirectoryFileHeader centralDirectoryFileHeader = new CentralDirectoryFileHeader();
+            centralDirectoryFileHeader.read(channel);
+
+            centralDirectoryFileHeader.setLocalHeaderOffset(centralDirectoryFileHeader.getLocalHeaderOffset());
+            assertEquals("local header offset", 0xFFFFFFFFL, centralDirectoryFileHeader.localHeaderOffset);
+        }
+    }
 }