fully automated reproducible space deterministic builds

scripts/Determinizer.java

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+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
+import java.util.jar.JarOutputStream;
+import java.util.stream.Collectors;
+
+/**
+ * Make a .jar file deterministic by sorting all entries by name, and setting all the last modified times to 0.
+ * This makes the build 100% reproducible since the timestamp when you built it no longer affects the final file.
+ * @author leijurv
+ */
+public class Determinizer {
+
+    public static void main(String[] args) throws IOException {
+        System.out.println("Input path: " + args[0] + " Output path: " + args[1]);
+        JarFile jarFile = new JarFile(new File(args[0]));
+        JarOutputStream jos = new JarOutputStream(new FileOutputStream(new File(args[1])));
+        ArrayList<JarEntry> entries = jarFile.stream().collect(Collectors.toCollection(ArrayList::new));
+        entries.sort(Comparator.comparing(JarEntry::getName));
+        for (JarEntry entry : entries) {
+            if (entry.getName().equals("META-INF/fml_cache_annotation.json")) {
+                continue;
+            }
+            if (entry.getName().equals("META-INF/fml_cache_class_versions.json")) {
+                continue;
+            }
+            JarEntry clone = new JarEntry(entry.getName());
+            clone.setTime(0);
+            jos.putNextEntry(clone);
+            copy(jarFile.getInputStream(entry), jos);
+        }
+        jos.finish();
+        jarFile.close();
+    }
+
+    public static void copy(InputStream is, OutputStream os) throws IOException {
+        byte[] buffer = new byte[1024];
+        int len;
+        while ((len = is.read(buffer)) != -1) {
+            os.write(buffer, 0, len);
+        }
+    }
+}