FirebaseEventProxy.java

/*
 * Copyright 2016 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.gaefirebaseeventproxy;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.appengine.api.utils.SystemProperty;
import com.google.firebase.FirebaseApp;
import com.google.firebase.FirebaseOptions;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.HashMap;
import java.util.Map;
import java.util.logging.Logger;

public class FirebaseEventProxy {

  private static final Logger log = Logger.getLogger(FirebaseEventProxy.class.getName());

  /**
   * FirebaseEventProxy.
   */
  public FirebaseEventProxy() {
    String firebaseLocation = "https://crackling-torch-392.firebaseio.com";
    Map<String, Object> databaseAuthVariableOverride = new HashMap<String, Object>();
    // uid and provider will have to match what you have in your firebase security rules
    databaseAuthVariableOverride.put("uid", "gae-firebase-event-proxy");
    databaseAuthVariableOverride.put("provider", "com.example");
    try {
      FirebaseOptions options =
          new FirebaseOptions.Builder()
              .setServiceAccount(new FileInputStream("gae-firebase-secrets.json"))
              .setDatabaseUrl(firebaseLocation)
              .setDatabaseAuthVariableOverride(databaseAuthVariableOverride)
              .build();
      FirebaseApp.initializeApp(options);
    } catch (IOException e) {
      throw new RuntimeException(
          "Error reading firebase secrets from file: src/main/webapp/gae-firebase-secrets.json: "
              + e.getMessage());
    }
  }

  /**
   * start the proxy.
   */
  @SuppressWarnings("VariableDeclarationUsageDistance")
  public void start() {
    DatabaseReference firebase = FirebaseDatabase.getInstance().getReference();

    // Subscribe to value events. Depending on use case, you may want to subscribe to child events
    // through childEventListener.
    firebase.addValueEventListener(
        new ValueEventListener() {
          @Override
          public void onDataChange(DataSnapshot snapshot) {
            if (snapshot.exists()) {
              try {
                // Convert value to JSON using Jackson
                String json = new ObjectMapper().writeValueAsString(snapshot.getValue(false));

                // Replace the URL with the url of your own listener app.
                URL dest = new URL("http://gae-firebase-listener-python.appspot.com/log");
                HttpURLConnection connection = (HttpURLConnection) dest.openConnection();
                connection.setRequestMethod("POST");
                connection.setDoOutput(true);

                // Rely on X-Appengine-Inbound-Appid to authenticate. Turning off redirects is
                // required to enable.
                connection.setInstanceFollowRedirects(false);

                // Fill out header if in dev environment
                if (SystemProperty.environment.value()
                    != SystemProperty.Environment.Value.Production) {
                  connection.setRequestProperty("X-Appengine-Inbound-Appid", "dev-instance");
                }

                // Put Firebase data into http request
                StringBuilder stringBuilder = new StringBuilder();
                stringBuilder.append("&fbSnapshot=");
                stringBuilder.append(URLEncoder.encode(json, "UTF-8"));
                connection.getOutputStream().write(stringBuilder.toString().getBytes());
                if (connection.getResponseCode() != 200) {
                  log.severe("Forwarding failed");
                } else {
                  log.info("Sent: " + json);
                }
              } catch (JsonProcessingException e) {
                log.severe("Unable to convert Firebase response to JSON: " + e.getMessage());
              } catch (IOException e) {
                log.severe("Error in connecting to app engine: " + e.getMessage());
              }
            }
          }

          @Override
          public void onCancelled(DatabaseError error) {
            log.severe("Firebase connection cancelled: " + error.getMessage());
          }
        });
  }
}