Group invite link epoch support.

libsignal/service/src/main/java/org/whispersystems/util/Base64UrlSafe.java

@@ -0,0 +1,34 @@
+package org.whispersystems.util;
+
+import java.io.IOException;
+
+public final class Base64UrlSafe {
+
+  private Base64UrlSafe() {
+  }
+
+  public static byte[] decode(String s) throws IOException {
+    return Base64.decode(s, Base64.URL_SAFE);
+  }
+
+  public static byte[] decodePaddingAgnostic(String s) throws IOException {
+    switch (s.length() % 4) {
+      case 1:
+      case 3: s = s + "="; break;
+      case 2: s = s + "=="; break;
+    }
+    return decode(s);
+  }
+
+  public static String encodeBytes(byte[] source) {
+    try {
+      return Base64.encodeBytes(source, Base64.URL_SAFE);
+    } catch (IOException e) {
+      throw new AssertionError(e);
+    }
+  }
+
+  public static String encodeBytesWithoutPadding(byte[] source) {
+    return encodeBytes(source).replace("=", "");
+  }
+}