Add OkHttp-specific client when its present on the classpath.

pom.xml

@@ -52,6 +52,7 @@
     <android.platform>16</android.platform>
     <gson.version>2.2.2</gson.version>
     <javax.inject.version>1</javax.inject.version>
+    <okhttp.version>1.0.1</okhttp.version>
 
     <!-- Test Dependencies -->
     <junit.version>4.10</junit.version>
@@ -105,6 +106,11 @@
         <artifactId>android</artifactId>
         <version>${android.version}</version>
       </dependency>
+      <dependency>
+        <groupId>com.squareup.okhttp</groupId>
+        <artifactId>okhttp</artifactId>
+        <version>${okhttp.version}</version>
+      </dependency>
       <dependency>
         <groupId>com.google.code.gson</groupId>
         <artifactId>gson</artifactId>

retrofit/pom.xml

@@ -25,6 +25,11 @@
       <artifactId>android</artifactId>
       <optional>true</optional>
     </dependency>
+    <dependency>
+      <groupId>com.squareup.okhttp</groupId>
+      <artifactId>okhttp</artifactId>
+      <optional>true</optional>
+    </dependency>
 
     <dependency>
       <groupId>junit</groupId>

retrofit/src/main/java/retrofit/http/Platform.java

@@ -10,6 +10,7 @@
 import retrofit.http.android.AndroidApacheClient;
 import retrofit.http.android.MainThreadExecutor;
 import retrofit.http.client.Client;
+import retrofit.http.client.OkClient;
 import retrofit.http.client.UrlConnectionClient;
 
 import static android.os.Process.THREAD_PRIORITY_BACKGROUND;
@@ -36,6 +37,7 @@ private static Platform findPlatform() {
   Converter defaultConverter() {
     return new GsonConverter(new Gson());
   }
+
   abstract Client.Provider defaultClient();
   abstract Executor defaultHttpExecutor();
   abstract Executor defaultCallbackExecutor();
@@ -44,7 +46,12 @@ Converter defaultConverter() {
   /** Provides sane defaults for operation on the JVM. */
   private static class Base extends Platform {
     @Override Client.Provider defaultClient() {
-      final Client client = new UrlConnectionClient();
+      final Client client;
+      if (hasOkHttpOnClasspath()) {
+        client = OkClientInstantiator.instantiate();
+      } else {
+        client = new UrlConnectionClient();
+      }
       return new Client.Provider() {
         @Override public Client get() {
           return client;
@@ -82,7 +89,9 @@ private static class Base extends Platform {
   private static class Android extends Platform {
     @Override Client.Provider defaultClient() {
       final Client client;
-      if (Build.VERSION.SDK_INT < Build.VERSION_CODES.GINGERBREAD) {
+      if (hasOkHttpOnClasspath()) {
+        client = OkClientInstantiator.instantiate();
+      } else if (Build.VERSION.SDK_INT < Build.VERSION_CODES.GINGERBREAD) {
         client = new AndroidApacheClient();
       } else {
         client = new UrlConnectionClient();
@@ -119,4 +128,24 @@ private static class Android extends Platform {
       };
     }
   }
+
+  /** Determine whether or not OkHttp is present on the runtime classpath. */
+  private static boolean hasOkHttpOnClasspath() {
+    try {
+      Class.forName("com.squareup.okhttp.OkHttpClient");
+      return true;
+    } catch (ClassNotFoundException e) {
+      return false;
+    }
+  }
+
+  /**
+   * Indirection for OkHttp class to prevent VerifyErrors on Android 2.0 and earlier when the
+   * dependency is not present..
+   */
+  private static class OkClientInstantiator {
+    static Client instantiate() {
+      return new OkClient();
+    }
+  }
 }

retrofit/src/main/java/retrofit/http/client/OkClient.java

@@ -0,0 +1,24 @@
+// Copyright 2013 Square, Inc.
+package retrofit.http.client;
+
+import com.squareup.okhttp.OkHttpClient;
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.URL;
+
+/** Retrofit client that uses OkHttp for communication. */
+public class OkClient extends UrlConnectionClient {
+  private final OkHttpClient client;
+
+  public OkClient() {
+    this(new OkHttpClient());
+  }
+
+  public OkClient(OkHttpClient client) {
+    this.client = client;
+  }
+
+  @Override protected HttpURLConnection openConnection(Request request) throws IOException {
+    return client.open(new URL(request.getUrl()));
+  }
+}

retrofit/src/main/java/retrofit/http/client/UrlConnectionClient.java

@@ -12,6 +12,7 @@
 import retrofit.http.mime.TypedInput;
 import retrofit.http.mime.TypedOutput;
 
+/** Retrofit client that uses {@link HttpURLConnection} for communication. */
 public class UrlConnectionClient implements Client {
   @Override public Response execute(Request request) throws IOException {
     HttpURLConnection connection = openConnection(request);