richardstephens · November 8, 2020 20:41 · Nov 8, 2020
diff --git a/RichUuid.java b/RichUuid.java
@@ -0,0 +1,82 @@
+package dev.richst.libs.richuuid;
+
+import java.io.*;
+import java.util.Base64;
+import java.util.UUID;
+
+public class RichUuid {
+    static byte[] uuidToByteArray(UUID uuid) {
+        try {
+            ByteArrayOutputStream bos = new ByteArrayOutputStream();
+            DataOutputStream dos = new DataOutputStream(bos);
+            dos.writeLong(uuid.getMostSignificantBits());
+            dos.writeLong(uuid.getLeastSignificantBits());
+            dos.write(2);
+            dos.flush();
+            return bos.toByteArray();
+        } catch (IOException ex) {
+            // this should never be thrown, and there is no sensible way to handle it
+            throw new IllegalStateException(
+                    "IO exception occurred working on memory backed streams", ex);
+        }
+    }
+
+    static UUID byteArrayToUuid(byte[] uuidBytes) {
+        try {
+            ByteArrayInputStream bis = new ByteArrayInputStream(uuidBytes);
+            DataInputStream dis = new DataInputStream(bis);
+            long msb = dis.readLong();
+            long lsb = dis.readLong();
+            return new UUID(msb, lsb);
+        } catch (IOException ex) {
+            // this should never be thrown, and there is no sensible way to handle it
+            throw new IllegalStateException(
+                    "IO exception occurred working on memory backed streams", ex);
+        }
+    }
+
+    public static String fromUUID(UUID uuid) {
+        byte[] uuidBytes = uuidToByteArray(uuid);
+        byte[] uuidBytesWithChecksum = new byte[18];
+        int checksum = 0;
+        for (int ii = 0; ii < 16; ii++) {
+            uuidBytesWithChecksum[ii] = uuidBytes[ii];
+            checksum += uuidBytes[ii] & 0xFF;
+        }
+        uuidBytesWithChecksum[16] = 0;
+        uuidBytesWithChecksum[17] = (byte) (checksum % 256);
+        return Base64.getUrlEncoder().encodeToString(uuidBytesWithChecksum);
+    }
+
+    public static String generate() {
+        return fromUUID(UUID.randomUUID());
+    }
+
+    private static boolean validateChecksum(byte[] uuidBytesWithChecksum) {
+        int checksum = 0;
+        for (int ii = 0; ii < 17; ii++) {
+            checksum += uuidBytesWithChecksum[ii] & 0xFF;
+        }
+        return ((byte) checksum) == uuidBytesWithChecksum[17];
+    }
+
+    private static void assertChecksumValid(byte[] uuidBytes) {
+        if (!validateChecksum(uuidBytes)) {
+            throw new InvalidRichUuidException("checksum invalid");
+        }
+    }
+
+    public static UUID toUUID(String richUuid) {
+        byte[] uuidBytesWithChecksum;
+        try {
+            uuidBytesWithChecksum = Base64.getUrlDecoder().decode(richUuid);
+        } catch (IllegalArgumentException ex) {
+            throw new InvalidRichUuidException("Could not base64 decode richUuid", ex);
+        }
+        if (uuidBytesWithChecksum.length != 18) {
+            throw new InvalidRichUuidException("UUID length invalid");
+        }
+        assertChecksumValid(uuidBytesWithChecksum);
+        return byteArrayToUuid(uuidBytesWithChecksum);
+    }
+}