Cronet: a framework for providing alternative Cronet implementations

components/cronet/android/api/src/org/chromium/net/CronetEngine.java

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.net;
 
 import android.content.Context;
 import android.net.http.HttpResponseCache;
 
 import java.io.IOException;
 import java.net.URL;
 import java.net.URLConnection;
 import java.net.URLStreamHandlerFactory;
 import java.util.Date;
+import java.util.List;
 import java.util.Set;
 import java.util.concurrent.Executor;
 
 import javax.net.ssl.HttpsURLConnection;
 /**
  * An engine to process {@link UrlRequest}s, which uses the best HTTP stack
  * available on the current platform. An instance of this class can be created
  * using {@link Builder}.
  */
 public abstract class CronetEngine {
@@ skipping 31 matching lines @@
          * {@link CronetEngine}. The default configuration enables HTTP/2 and
          * disables QUIC, SDCH and the HTTP cache.
          *
          * @param context Android {@link Context}, which is used by
          *                {@link Builder} to retrieve the application
          *                context. A reference to only the application
          *                context will be kept, so as to avoid extending
          *                the lifetime of {@code context} unnecessarily.
          */
         public Builder(Context context) {
-            mBuilderDelegate = ImplLoader.load(context);
+            CronetProviders providers = CronetProviders.instance();
+
+            // Check that there is at least one available provider.
+            List<CronetProvider> providerList = providers.getAvailableProviders(context);
+            if (providerList.size() == 0) {
+                throw new RuntimeException("Unable to find any Cronet provider."
+                        + " Have you included all necessary jars?");
+            }

[pauljensen, 2017/01/18 17:03:04]

nit: how about we get rid of this if statement, the if statement on line 87
should catch this and the exception message includes the provider list?

[kapishnikov, 2017/01/19 01:25:24]

I added more error messages in a new PS ad some extra logic of filtering out
disabled providers from the list, so the final list is different from the
original one. PTAL. Some messages can be compacted into a single message but I
wanted to be more verbose.

+
+            // Try to load implementation using available providers. Assuming that
+            // providers in the beginning of the list have higher priority.
+            ICronetEngineBuilder builderDelegate = null;
+            for (CronetProvider provider : providerList) {
+                Builder builder = provider.createBuilder();
+                if (builder != null) {
+                    builderDelegate = builder.mBuilderDelegate;
+                    break;
+                }
+            }
+
+            if (builderDelegate == null) {
+                throw new RuntimeException("Unable to load any Cronet implementation."
+                        + " The list of available providers: " + providerList);

[mef, 2017/01/18 20:57:54]

CronetProvider probably needs a meaningful toString() method for this.

[kapishnikov, 2017/01/19 01:25:24]

Good point. It will give the name of the class but having toString() with more
info is better. Done.

+            }
+
+            mBuilderDelegate = builderDelegate;

[pauljensen, 2017/01/18 17:03:04]

nit: perhaps change the body of this function to
this(createBuilderDelegate(context))

[kapishnikov, 2017/01/19 01:25:24]

Good idea. Done.

         }
 
         /**
+         * Constructs {@link Builder} with a given delegate that provides the actual implementation
+         * of the {@code Builder} methods. This constructor is used only by the internal
+         * implementation.
+         *
+         * @param builderDelegate delegate that provides the actual implementation.
+         *
+         * {@hide}
+         */
+        public Builder(ICronetEngineBuilder builderDelegate) {
+            mBuilderDelegate = builderDelegate;
+        }
+
+        /**
          * Constructs a User-Agent string including application name and version,
          * system build version, model and id, and Cronet version.
          *
          * @return User-Agent string.
          */
         public String getDefaultUserAgent() {
             return mBuilderDelegate.getDefaultUserAgent();
         }
 
         /**
@@ skipping 319 matching lines @@
      * thread calling {@link Executor#execute} to prevent blocking networking
      * operations and causing exceptions during shutdown.
      *
      * @param url URL for the generated requests.
      * @param callback callback object that gets invoked on different events.
      * @param executor {@link Executor} on which all callbacks will be invoked.
      */
     public abstract UrlRequest.Builder newUrlRequestBuilder(
             String url, UrlRequest.Callback callback, Executor executor);
 }