ServiceConfigSupplier.java

/*
 * Copyright 2016 Google Inc. All Rights Reserved.
 *
 * 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.google.api.config;

import com.google.api.Service;
import com.google.api.Service.Builder;
import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
import com.google.api.client.http.HttpRequest;
import com.google.api.client.http.HttpRequestInitializer;
import com.google.api.client.http.HttpResponse;
import com.google.api.client.http.HttpStatusCodes;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.json.jackson2.JacksonFactory;
import com.google.api.services.servicemanagement.ServiceManagement;
import com.google.api.services.servicemanagement.model.ListServiceConfigsResponse;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Joiner;
import com.google.common.base.Preconditions;
import com.google.common.base.Strings;
import com.google.common.base.Supplier;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.protobuf.util.JsonFormat;

import java.io.IOException;
import java.text.MessageFormat;
import java.util.List;

import javax.annotation.Nullable;

/**
 * Supplies a service configuration fetched from Google Service Management APIs.
 */
public final class ServiceConfigSupplier implements Supplier<Service> {
  private static final String SERVICE_NAME_KEY = "ENDPOINTS_SERVICE_NAME";
  private static final String SERVICE_VERSION_KEY = "ENDPOINTS_SERVICE_VERSION";
  private static final ImmutableMap<Integer, String> ERROR_CODE_DETAILS =
      ImmutableMap.<Integer, String>builder()
          .put(
              403 /* forbidden */,
              "This may occur if the App Engine service account has been deleted or does not " +
              "have correct permissions. Visit https://goo.gl/UEKik4 and verify that the " +
              "App Engine default service account has either the Editor or Service Controller " +
              "role.")
          .put(
              404 /* not found */,
              "The service config name and config id could not be found. Double check that " +
              "filter initialization parameters endpoints.projectId and endpoints.serviceName " +
              "are correctly set. See https://goo.gl/yp8QUN for details.")
          .put(
              429 /* too many requests */,
              "Too many requests are being made to fetch the service config. Check to see if " +
              "instances are crashing prematurely. If not, you may need to increase your " +
              "Google Service Management API quota. See https://goo.gl/JjBQMu to manage quota.")
          .build();

  private static final List<String> SCOPES =
      ImmutableList.of("https://www.googleapis.com/auth/cloud-platform");

  private static final String FIELD_MASKS = Joiner.on(',').join(
      "authentication",
      "http",
      "id",
      "logging",
      "logs",
      "metrics",
      "monitored_resources",
      "monitoring",
      "name",
      "producer_project_id",
      "quota",
      "system_parameters",
      "usage");

  private final Environment environment;
  private final ServiceManagement serviceManagement;

  @VisibleForTesting
  ServiceConfigSupplier(
      Environment environment,
      HttpTransport httpTransport,
      JsonFactory jsonFactory,
      final GoogleCredential credential) {
    this.environment = environment;
    HttpRequestInitializer requestInitializer = new HttpRequestInitializer() {
      @Override
      public void initialize(HttpRequest request) throws IOException {
        request.setThrowExceptionOnExecuteError(false);
        credential.initialize(request);
      }
    };
    this.serviceManagement =
        new ServiceManagement.Builder(httpTransport, jsonFactory, requestInitializer)
            .setApplicationName("Endpoints Frameworks Java")
            .build();
  }

  /**
   * Fetches the service configuration using the service name and the service
   * version read from the environment variables.
   *
   * @return a {@link Service} object generated by the JSON response from Google
   * Service Management.
   */
  @Override
  public Service get() {
    String serviceName = this.environment.getVariable(SERVICE_NAME_KEY);
    if (Strings.isNullOrEmpty(serviceName)) {
      String errorMessage =
          String.format("Environment variable '%s' is not set", SERVICE_NAME_KEY);
      throw new IllegalArgumentException(errorMessage);
    }
    String serviceVersion = this.environment.getVariable(SERVICE_VERSION_KEY);

    return fetch(serviceName, serviceVersion);
  }

  /**
   * Fetches the service configuration with the given service name and service version.
   *
   * @param serviceName the given service name
   * @param serviceVersion the given service version
   * @return a {@link Service} object generated by the JSON response from Google Service Management.
   */
  private Service fetch(String serviceName, @Nullable String serviceVersion) {
    Preconditions.checkArgument(
        !Strings.isNullOrEmpty(serviceName), "service name must be specified");

    if (serviceVersion == null) {
      serviceVersion = fetchLatestServiceVersion(serviceName);
    }

    final HttpResponse httpResponse;
    try {
      httpResponse = serviceManagement.services().configs().get(serviceName, serviceVersion)
          .setFields(FIELD_MASKS)
          .executeUnparsed();
    } catch (IOException exception) {
      throw new ServiceConfigException(exception);
    }

    int statusCode = httpResponse.getStatusCode();
    if (statusCode != HttpStatusCodes.STATUS_CODE_OK) {
      String extendedMessage = ERROR_CODE_DETAILS.get(statusCode);
      String message = MessageFormat.format(
          "Failed to fetch service config (status code {0})",
          statusCode);
      if (extendedMessage != null) {
        message = String.format("%s: %s", message, extendedMessage);
      }
      throw new ServiceConfigException(message);
    }

    Service service = parseHttpResponse(httpResponse);
    validateServiceConfig(service, serviceName, serviceVersion);

    return service;
  }

  private String fetchLatestServiceVersion(String serviceName) {
    try {
      ListServiceConfigsResponse response =
          serviceManagement.services().configs().list(serviceName).execute();
      if (response.getServiceConfigs() == null || response.getServiceConfigs().isEmpty()) {
        throw new ServiceConfigException(MessageFormat.format(
            "Failed to fetch default config version for service ''{0}''. No versions exist!",
            serviceName));
      }
      return response.getServiceConfigs().get(0).getId();
    } catch (IOException e) {
      throw new ServiceConfigException(e);
    }
  }

  private static Service parseHttpResponse(HttpResponse httpResponse) {
    try {
      Builder builder = Service.newBuilder();
      JsonFormat.parser().ignoringUnknownFields().merge(httpResponse.parseAsString(), builder);
      return builder.build();
    } catch (IOException exception) {
      throw new ServiceConfigException(
          "Failed to parse the HTTP response as service configuration",
          exception);
    }
  }

  private static void validateServiceConfig(
      Service service,
      String expectedServiceName,
      @Nullable String expectedServiceVersion) {
    String serviceName = service.getName();
    if (!expectedServiceName.equals(serviceName)) {
      throw new ServiceConfigException("Unexpected service name in service config: " + serviceName);
    }

    String serviceVersion = service.getId();
    if (expectedServiceVersion != null && !expectedServiceVersion.equals(serviceVersion)) {
      throw new ServiceConfigException("Unexpected service version in service config: " + serviceVersion);
    }
  }

  /**
   * Create a {@link ServiceConfigSupplier} instance.
   *
   * @return a {@code ServiceConfigSuppler}
   */
  public static ServiceConfigSupplier create() {
    NetHttpTransport httpTransport = new NetHttpTransport();
    JacksonFactory jsonFactory = new JacksonFactory();
    GoogleCredential credential;
    try {
      credential = GoogleCredential.getApplicationDefault(httpTransport, jsonFactory)
          .createScoped(SCOPES);
    } catch (IOException e) {
      throw new IllegalStateException("could not get credentials for fetching service config!");
    }
    return new ServiceConfigSupplier(
        new SystemEnvironment(), httpTransport, jsonFactory, credential);
  }

  private static final class SystemEnvironment implements Environment {
    @Override
    public String getVariable(String variableName) {
      return System.getenv(variableName);
    }
  }
}