[android] export seed constant

android/src/main/java/com/bitgo/randombytes/RandomBytesModule.java

@@ -7,10 +7,13 @@ import com.facebook.react.bridge.Callback;
 import com.facebook.react.bridge.ReactContextBaseJavaModule;
 
 import java.security.SecureRandom;
+import java.util.Map;
+import java.util.HashMap;
 
 import android.util.Base64;
 
 class RandomBytesModule extends ReactContextBaseJavaModule {
+  private static final String SEED_KEY = "seed";
 
   public RandomBytesModule(ReactApplicationContext reactContext) {
     super(reactContext);
@@ -20,12 +23,23 @@ class RandomBytesModule extends ReactContextBaseJavaModule {
   public String getName() {
     return "RNRandomBytes";
   }
+
   @ReactMethod
   public void randomBytes(int size, Callback success) {
+    success.invoke(null, getRandomBytes(size));
+  }
+
+  @Override
+  public Map<String, Object> getConstants() {
+    final Map<String, Object> constants = new HashMap<>();
+    constants.put(SEED_KEY, getRandomBytes(4096));
+    return constants;
+  }
+
+  private String getRandomBytes(int size) {
     SecureRandom sr = new SecureRandom();
     byte[] output = new byte[size];
     sr.nextBytes(output);
-    String string = Base64.encodeToString(output, Base64.DEFAULT);
-    success.invoke(null, string);
+    return Base64.encodeToString(output, Base64.DEFAULT);
   }
 }