Fix timestamp roundtripping issue (#36)

* Fix timestamp roundtripping issue

* remove stray comment

---------

Co-authored-by: Oscar Boykin <oboykin@netflix.com>

src/main/java/com/github/johnynek/jarjar/util/StandaloneJarProcessor.java

@@ -25,6 +25,13 @@
 
 public class StandaloneJarProcessor
 {
+    // this repairs the incorrect UTC on write, but Local on read
+    // timestamp. Apply this to a read timestamp before writing
+    // see: https://github.com/eed3si9n/jarjar-abrams/pull/37/files#r1344693775
+    public static long fixTimestamp(long ts) {
+        return ts - java.util.TimeZone.getDefault().getOffset(ts);
+    }
+
     public static void run(File from, File to, JarProcessor proc, Boolean warnOnDuplicateClass) throws IOException {
         byte[] buf = new byte[0x2000];
 
@@ -39,7 +46,11 @@ public static void run(File from, File to, JarProcessor proc, Boolean warnOnDupl
                 EntryStruct struct = new EntryStruct();
                 JarEntry entry = e.nextElement();
                 struct.name = entry.getName();
-                struct.time = entry.getTime();
+                // In the JDK, getTime converts the dos time in the zip
+                // into local time using a deprecated Date api that uses
+                // the default timezone, which often won't be UTC.
+                // but when setting, it assumes we are in UTC.
+                struct.time = fixTimestamp(entry.getTime());
                 ByteArrayOutputStream baos = new ByteArrayOutputStream();
                 IoUtil.pipe(in.getInputStream(entry), baos, buf);
                 struct.data = baos.toByteArray();

src/test/java/com/github/johnynek/jarjar/BUILD

@@ -58,3 +58,14 @@ java_test(
         "//src/main/java/com/github/johnynek/jarjar",
     ],
 )
+
+java_test(
+    name = "TimestampFixTest",
+    srcs = ["TimestampFixTest.java"],
+    test_class = "com.github.johnynek.jarjar.TimestampFixTest",
+    deps = [
+        "@bazel_jar_jar_asm//jar",
+        "@bazel_jar_jar_asm_commons//jar",
+        "//src/main/java/com/github/johnynek/jarjar",
+    ],
+)

src/test/java/com/github/johnynek/jarjar/TimestampFixTest.java

@@ -0,0 +1,35 @@
+package com.github.johnynek.jarjar;
+
+import java.util.jar.JarEntry;
+import junit.framework.TestCase;
+import org.junit.Test;
+import com.github.johnynek.jarjar.util.StandaloneJarProcessor;
+import java.util.jar.JarOutputStream;
+import java.util.jar.JarInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.ByteArrayInputStream;
+
+public class TimestampFixTest extends TestCase {
+    @Test
+    public void testTimestampFix() throws java.io.IOException {
+      ByteArrayOutputStream baos = new ByteArrayOutputStream();
+      JarOutputStream out = new JarOutputStream(baos);
+      JarEntry je = new JarEntry("foo.txt");
+      // we can only have second resolution
+      long nowSeconds = System.currentTimeMillis() / 1000;
+      if ((nowSeconds & 1L) == 1L) {
+        // make sure we have an even timestamp
+        nowSeconds -= 1L;
+      }
+      long startTime = (nowSeconds * 1000);
+      je.setTime(startTime); 
+      out.putNextEntry(je);
+      out.write(new byte[]{});
+      out.close();
+      JarInputStream in = new JarInputStream(new ByteArrayInputStream(baos.toByteArray()));
+      je = in.getNextJarEntry();
+      long readTime = StandaloneJarProcessor.fixTimestamp(je.getTime());
+      assertEquals(startTime, readTime);
+    }
+
+}