1 files changed, 58 insertions, 0 deletions
diff --git a/mobile/android/geckoview/src/main/java/org/mozilla/gecko/util/EventCallback.java b/mobile/android/geckoview/src/main/java/org/mozilla/gecko/util/EventCallback.java
new file mode 100644
index 0000000000..3ef469ac1b
--- /dev/null
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/gecko/util/EventCallback.java
@@ -0,0 +1,58 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko.util;
+
+import androidx.annotation.Nullable;
+import org.mozilla.gecko.annotation.RobocopTarget;
+import org.mozilla.gecko.annotation.WrapForJNI;
+import org.mozilla.geckoview.GeckoResult;
+
+/**
+ * Callback interface for Gecko requests.
+ *
+ * <p>For each instance of EventCallback, exactly one of sendResponse, sendError, or sendCancel must
+ * be called to prevent observer leaks. If more than one send* method is called, or if a single send
+ * method is called multiple times, an {@link IllegalStateException} will be thrown.
+ */
+@RobocopTarget
+@WrapForJNI(calledFrom = "gecko")
+public interface EventCallback {
+  /**
+   * Sends a success response with the given data.
+   *
+   * @param response The response data to send to Gecko. Can be any of the types accepted by
+   *     JSONObject#put(String, Object).
+   */
+  void sendSuccess(Object response);
+
+  /**
+   * Sends an error response with the given data.
+   *
+   * @param response The response data to send to Gecko. Can be any of the types accepted by
+   *     JSONObject#put(String, Object).
+   */
+  void sendError(Object response);
+
+  /**
+   * Resolve this Event callback with the result from the {@link GeckoResult}.
+   *
+   * @param response the result that will be used for this callback.
+   */
+  default <T> void resolveTo(final @Nullable GeckoResult<T> response) {
+    if (response == null) {
+      sendSuccess(null);
+      return;
+    }
+    response.accept(
+        this::sendSuccess,
+        throwable -> {
+          // Don't propagate Errors, just crash
+          if (!(throwable instanceof Exception)) {
+            throw new GeckoResult.UncaughtException(throwable);
+          }
+          sendError(throwable.getMessage());
+        });
+  }
+}