networking: Fix requests failing when turning network off and on facebook#19709.

This bug is probably actually a bug in OkHttp: square/okhttp#4079
Both issues linked above contain extensive details about the issue, its likely origins and
how to reproduce it. A short summary of the issue and the fix in this commit:

On Android, disconnecting from the network somehow corrupts the idle connections in okhttp
clients. New requests made over these clients fail. This commit works around that bug by
clearing the idle connection pool of each client when Android disconnects from the network.

Author: roberthoenig

ReactAndroid/src/main/java/com/facebook/react/ReactActivity.java

@@ -9,14 +9,18 @@
 
 import javax.annotation.Nullable;
 
+import android.Manifest;
 import android.app.Activity;
 import android.content.Intent;
+import android.content.pm.PackageManager;
 import android.os.Bundle;
+import android.support.v4.content.ContextCompat;
 import android.view.KeyEvent;
 
 import com.facebook.react.modules.core.DefaultHardwareBackBtnHandler;
 import com.facebook.react.modules.core.PermissionAwareActivity;
 import com.facebook.react.modules.core.PermissionListener;
+import com.facebook.react.modules.network.OkHttpClientProvider;
 
 /**
  * Base Activity for React Native applications.
@@ -50,6 +54,10 @@ protected ReactActivityDelegate createReactActivityDelegate() {
   protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     mDelegate.onCreate(savedInstanceState);
+    if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_NETWORK_STATE)
+        == PackageManager.PERMISSION_GRANTED) {
+      OkHttpClientProvider.addNetworkListenerToEvictIdleConnectionsOnNetworkChange(getApplicationContext());
+    }
   }
 
   @Override

ReactAndroid/src/main/java/com/facebook/react/modules/network/OkHttpClientProvider.java

@@ -7,12 +7,25 @@
 
 package com.facebook.react.modules.network;
 
+import android.content.BroadcastReceiver;
+import android.content.Context;
+import android.content.Intent;
+import android.content.IntentFilter;
+import android.net.ConnectivityManager;
+import android.net.NetworkInfo;
+import android.os.AsyncTask;
 import android.os.Build;
+import android.os.Bundle;
 
 import com.facebook.common.logging.FLog;
+import com.facebook.react.ReactActivity;
+import com.facebook.react.bridge.ReactApplicationContext;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
+import java.util.Set;
+import java.util.WeakHashMap;
 import java.util.concurrent.TimeUnit;
 
 import javax.annotation.Nullable;
@@ -33,6 +46,9 @@ public class OkHttpClientProvider {
   // User-provided OkHttpClient factory
   private static @Nullable OkHttpClientFactory sFactory;
 
+  private final static Set<OkHttpClient> sClients = Collections.newSetFromMap(
+    new WeakHashMap<OkHttpClient, Boolean>());
+
   public static void setOkHttpClientFactory(OkHttpClientFactory factory) {
     sFactory = factory;
   }
@@ -43,6 +59,38 @@ public static OkHttpClient getOkHttpClient() {
     }
     return sClient;
   }
+
+  private static class EvictIdleConnectionsTask extends AsyncTask {
+    @Override
+    protected Object doInBackground(Object[] objects) {
+      for (OkHttpClient client: sClients) {
+        client.connectionPool().evictAll();
+      }
+      return null;
+    }
+  }
+
+  /*
+    See https://github.com/facebook/react-native/issues/19709 for context.
+    We know that idle connections get corrupted when the connectivity state
+    changes to disconnected, but the debugging of this issue hasn't been
+    exhaustive and it's possible that other changes in connectivity also
+    corrupt idle connections. `CONNECTIVITY_ACTION`s occur infrequently
+    enough to go safe and evict all idle connections on every such action.
+   */
+  public static void addNetworkListenerToEvictIdleConnectionsOnNetworkChange(Context context) {
+    final BroadcastReceiver br = new BroadcastReceiver() {
+      @Override
+      public void onReceive(Context context, Intent intent) {
+        if (intent.getAction().equals(ConnectivityManager.CONNECTIVITY_ACTION)) {
+          new EvictIdleConnectionsTask().execute();
+        }
+      }
+    };
+    final IntentFilter intentFilter = new IntentFilter();
+    intentFilter.addAction(ConnectivityManager.CONNECTIVITY_ACTION);
+    context.registerReceiver(br, intentFilter);
+  }
 
   // okhttp3 OkHttpClient is immutable
   // This allows app to init an OkHttpClient with custom settings.
@@ -54,7 +102,11 @@ public static OkHttpClient createClient() {
     if (sFactory != null) {
       return sFactory.createNewNetworkModuleClient();
     }
-    return createClientBuilder().build();
+    else {
+      final OkHttpClient client = createClientBuilder().build();
+      registerClientToEvictIdleConnectionsOnNetworkChange(client);
+      return client;
+    }
   }
 
   public static OkHttpClient.Builder createClientBuilder() {
@@ -68,6 +120,10 @@ public static OkHttpClient.Builder createClientBuilder() {
     return enableTls12OnPreLollipop(client);
   }
 
+  public static void registerClientToEvictIdleConnectionsOnNetworkChange(OkHttpClient client) {
+    sClients.add(client);
+  }
+
   /*
     On Android 4.1-4.4 (API level 16 to 19) TLS 1.1 and 1.2 are
     available but not enabled by default. The following method