add configureReproducible( Date lastModifiedDate ) API

this closes #121

src/main/java/org/codehaus/plexus/archiver/AbstractArchiver.java

@@ -1257,4 +1257,45 @@ public String getOverrideGroupName()
     {
         return overrideGroupName;
     }
+
+    @Override
+    public void configureReproducible( Date lastModifiedDate )
+    {
+        // 1. force last modified date
+        setLastModifiedDate( normalizeLastModifiedDate( lastModifiedDate ) );
+
+        // 2. sort filenames in each directory when scanning filesystem
+        setFilenameComparator( new Comparator<String>()
+        {
+            @Override
+            public int compare( String s1, String s2 )
+            {
+                return s1.compareTo( s2 );
+            }
+        } );
+
+        // 3. ignore file/directory mode from filesystem, since they may vary based on local user umask
+        // notice: this overrides execute bit on Unix (that is already ignored on Windows)
+        setFileMode( Archiver.DEFAULT_FILE_MODE );
+        setDirectoryMode( Archiver.DEFAULT_DIR_MODE );
+
+        // 4. ignore uid/gid from filesystem (for tar)
+        setOverrideUid( 0 );
+        setOverrideUserName( "root" ); // is it possible to avoid this, like "tar --numeric-owner"?
+        setOverrideGid( 0 );
+        setOverrideGroupName( "root" );
+    }
+
+    /**
+     * Normalize last modified time value to get reproducible archive entries, based on
+     * archive binary format (tar uses UTC timestamp but zip uses local time then requires
+     * tweaks to make the value reproducible whatever the current timezone is).
+     *
+     * @param lastModifiedDate 
+     * @return
+     */
+    protected Date normalizeLastModifiedDate( Date lastModifiedDate )
+    {
+        return lastModifiedDate;
+    }
 }

src/main/java/org/codehaus/plexus/archiver/Archiver.java

@@ -415,6 +415,9 @@ ResourceIterator getResources()
     Date getLastModifiedDate();
 
     /**
+     * Set filename comparator, used to sort file entries when scanning directories since File.list() does not
+     * guarantee any order.
+     *
      * @since 4.2.0
      */
     void setFilenameComparator( Comparator<String> filenameComparator );
@@ -458,4 +461,18 @@ ResourceIterator getResources()
      * @since 4.2.0
      */
     String getOverrideGroupName();
+
+    /**
+     * Configure the archiver to create archives in a reproducible way (see <a
+     * href="https://reproducible-builds.org/>Reproducible Builds</a>). This will configure:
+     * <ul>
+     * <li>reproducible archive entries order,</li>
+     * <li>defined entries timestamp</li>
+     * <li>and reproducible entries Unix mode.</li>
+     * <ul>
+     * 
+     * @param lastModifiedDate the date to use for archive entries last modified time
+     * @since 4.2.0
+     */
+    void configureReproducible( Date lastModifiedDate );
 }

src/main/java/org/codehaus/plexus/archiver/diags/DelgatingArchiver.java

@@ -398,4 +398,11 @@ public String getOverrideGroupName()
     {
         return target.getOverrideGroupName();
     }
+
+    @Override
+    public void configureReproducible( Date lastModifiedDate )
+    {
+        target.configureReproducible( lastModifiedDate );
+    }
+
 }

src/main/java/org/codehaus/plexus/archiver/diags/NoOpArchiver.java

@@ -414,4 +414,10 @@ public String getOverrideGroupName()
         return null;
     }
 
+    @Override
+    public void configureReproducible( Date lastModifiedDate )
+    {
+
+    }
+
 }

src/main/java/org/codehaus/plexus/archiver/diags/TrackingArchiver.java

@@ -468,4 +468,9 @@ public String getOverrideGroupName()
     {
         return null;
     }
+
+    @Override
+    public void configureReproducible( Date lastModifiedDate )
+    {
+    }
 }

src/main/java/org/codehaus/plexus/archiver/zip/AbstractZipArchiver.java

@@ -24,6 +24,8 @@
 import java.io.OutputStream;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
+import java.util.Calendar;
+import java.util.Date;
 import java.util.Hashtable;
 import java.util.Stack;
 import java.util.concurrent.ExecutionException;
@@ -833,4 +835,24 @@ protected String getArchiveType()
         return archiveType;
     }
 
+    @Override
+    protected Date normalizeLastModifiedDate( Date lastModifiedDate )
+    {
+        // timestamp of zip entries at zip storage level ignores timezone: managed in ZipEntry.setTime,
+        // that turns javaToDosTime: need to revert the operation here to get reproducible
+        // zip entry time
+        return new Date( dosToJavaTime( lastModifiedDate.getTime() ) );
+    }
+
+    /**
+     * Converts DOS time to Java time (number of milliseconds since epoch).
+     *
+     * @see java.util.zip.ZipEntry#setTime
+     * @see java.util.zip.ZipUtils#dosToJavaTime
+     */
+    private static long dosToJavaTime( long dosTime )
+    {
+        Calendar cal = Calendar.getInstance();
+        return dosTime - ( cal.get( Calendar.ZONE_OFFSET ) + cal.get( Calendar.DST_OFFSET ) );
+    }
 }