Add SelectedProtocolQuerier to get protocol selected by NPN on Android.

Fixes #467

Manually tested by using NPN on Android 4.3 (api level 18) talk to GFE.

okhttp/src/main/java/com/squareup/okhttp/OkHttpTlsUpgrader.java

@@ -34,6 +34,7 @@ package com.squareup.okhttp;
 import com.google.common.base.Preconditions;
 
 import com.squareup.okhttp.internal.Platform;
+import com.squareup.okhttp.internal.SelectedProtocolQuerier;
 
 import java.io.IOException;
 import java.net.InetSocketAddress;
@@ -75,22 +76,15 @@ public final class OkHttpTlsUpgrader {
 
     Platform platform = Platform.get();
 
-    String negotiatedProtocol = null;
-    try {
     // It's possible that the user provided SSLSocketFactory has already done the handshake
     // when creates the SSLSocket.
-      negotiatedProtocol = platform.getSelectedProtocol(sslSocket);
-    } catch (Exception e) {
-      // In some implementations, querying selected protocol before the handshake will fail with
-      // exception.
-    }
+    String negotiatedProtocol = SelectedProtocolQuerier.getSelectedProtocol(sslSocket);
     if (negotiatedProtocol == null) {
-
       try {
         // Force handshake.
         sslSocket.startHandshake();
 
-        negotiatedProtocol = platform.getSelectedProtocol(sslSocket);
+        negotiatedProtocol = SelectedProtocolQuerier.getSelectedProtocol(sslSocket);
         if (negotiatedProtocol == null) {
           throw new RuntimeException("protocol negotiation failed");
         }

okhttp/src/main/java/com/squareup/okhttp/internal/SelectedProtocolQuerier.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2014, Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *    * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *    * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *
+ *    * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.squareup.okhttp.internal;
+
+import java.net.Socket;
+
+import javax.net.ssl.SSLSocket;
+
+/**
+ * A helper class located in package com.squareup.okhttp.internal for getting protocol
+ * selected by NPN on Android.
+ */
+public class SelectedProtocolQuerier {
+  private static Platform platform = Platform.get();
+
+  // byte[] getNpnSelectedProtocol()
+  private static final OptionalMethod<Socket> GET_NPN_SELECTED_PROTOCOL =
+      new OptionalMethod<Socket>(byte[].class, "getNpnSelectedProtocol");
+  private static boolean android;
+
+  /** Returns the negotiated protocol, or null if no protocol was negotiated. */
+  public static String getSelectedProtocol(SSLSocket socket) {
+    String protocol = null;
+    try {
+      protocol = platform.getSelectedProtocol(socket);
+    } catch (Exception e) {
+      // In some implementations, querying selected protocol before the handshake will fail with
+      // exception.
+    }
+    if (protocol == null && android && GET_NPN_SELECTED_PROTOCOL.isSupported(socket)) {
+      byte[] result = (byte[]) GET_NPN_SELECTED_PROTOCOL.invokeWithoutCheckedException(socket);
+      if (result != null) {
+        protocol = new String(result, Util.UTF_8);
+      }
+    }
+    return protocol;
+  }
+
+  static {
+    android = true;
+    try {
+      // Attempt to find Android 2.3+ APIs.
+      Class.forName("com.android.org.conscrypt.OpenSSLSocketImpl");
+    } catch (ClassNotFoundException ignored) {
+      try {
+        // Older platform before being unbundled.
+        Class.forName("org.apache.harmony.xnet.provider.jsse.OpenSSLSocketImpl");
+      } catch (ClassNotFoundException ignored2) {
+        android = false;
+      }
+    }
+  }
+}