PeerConnection(java): rationalize pointer-to-jlong conversion.

In r4665 I went a bit crazy with the manual reinterpretation of a pointer to a
jlong (to avoid undefined behavior) but that's what reinterpret_cast<> is for.
So use it directly now.
Added a do-nothing DataChannel to AppRTCDemo to regression test this, since the
only repro I've found of the original bug requires ARM ABI (PeerConnectionTest
on ia32 fails to repro).

BUG=2302
R=henrike@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/5489004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5269 4adac7df-926f-26a2-2b94-8c16560cd09d

talk/app/webrtc/java/jni/peerconnection_jni.cc

@@ -195,22 +195,18 @@ static JNIEnv* AttachCurrentThreadIfNeeded() {
   return jni;
 }
 
-// Return a |jlong| that will automatically convert back to |ptr| when assigned
-// to a |uint64|
+// Return a |jlong| that will correctly convert back to |ptr|.  This is needed
+// because the alternative (of silently passing a 32-bit pointer to a vararg
+// function expecting a 64-bit param) picks up garbage in the high 32 bits.
 static jlong jlongFromPointer(void* ptr) {
-  COMPILE_ASSERT(sizeof(intptr_t) <= sizeof(uint64),
+  COMPILE_ASSERT(sizeof(intptr_t) <= sizeof(jlong),
                  Time_to_rethink_the_use_of_jlongs);
-  // Guaranteed to fit by the COMPILE_ASSERT above.
-  uint64 u64 = reinterpret_cast<intptr_t>(ptr);
-  // If the unsigned value fits in the signed type, return it directly.
-  if (u64 <= std::numeric_limits<int64>::max())
-    return u64;
-  // Otherwise, we need to get move u64 into the range of [int64min, -1] subject
-  // to the constraints of remaining equal to |u64| modulo |2^64|.
-  u64 = std::numeric_limits<uint64>::max() - u64;  // In [0,int64max].
-  int64 i64 = -u64; // In [-int64max, 0].
-  i64 -= 1; // In [int64min, -1], and i64+2^64==u64.
-  return i64;
+  // Going through intptr_t to be obvious about the definedness of the
+  // conversion from pointer to integral type.  intptr_t to jlong is a standard
+  // widening by the COMPILE_ASSERT above.
+  jlong ret = reinterpret_cast<intptr_t>(ptr);
+  assert(reinterpret_cast<void*>(ret) == ptr);
+  return ret;
 }
 
 // Android's FindClass() is trickier than usual because the app-specific
@@ -1104,7 +1100,7 @@ JOW(jlong, DataChannel_registerObserverNative)(
   talk_base::scoped_ptr<DataChannelObserverWrapper> observer(
       new DataChannelObserverWrapper(jni, j_observer));
   ExtractNativeDC(jni, j_dc)->RegisterObserver(observer.get());
-  return reinterpret_cast<jlong>(observer.release());
+  return jlongFromPointer(observer.release());
 }
 
 JOW(void, DataChannel_unregisterObserverNative)(

talk/app/webrtc/javatests/src/org/webrtc/PeerConnectionTest.java

@@ -533,9 +533,11 @@ public class PeerConnectionTest extends TestCase {
         factory, offeringPC, videoSource, "oLMS", "oLMSv0", "oLMSa0",
         offeringExpectations);
 
-    offeringExpectations.setDataChannel(offeringPC.createDataChannel(
-        "offeringDC", new DataChannel.Init()));
+    DataChannel offeringDC = offeringPC.createDataChannel(
+        "offeringDC", new DataChannel.Init());
+    assertEquals("offeringDC", offeringDC.label());
 
+    offeringExpectations.setDataChannel(offeringDC);
     SdpObserverLatch sdpLatch = new SdpObserverLatch();
     offeringPC.createOffer(sdpLatch, new MediaConstraints());
     assertTrue(sdpLatch.await());

talk/examples/android/src/org/appspot/apprtc/AppRTCDemoActivity.java

@@ -171,11 +171,26 @@ public class AppRTCDemoActivity extends Activity
     }
   }
 
+
+  // Just for fun (and to regression-test bug 2302) make sure that DataChannels
+  // can be created, queried, and disposed.
+  private static void createDataChannelToRegressionTestBug2302(
+      PeerConnection pc) {
+    DataChannel dc = pc.createDataChannel("dcLabel", new DataChannel.Init());
+    abortUnless("dcLabel".equals(dc.label()), "WTF?");
+    dc.dispose();
+  }
+
   @Override
   public void onIceServers(List<PeerConnection.IceServer> iceServers) {
     factory = new PeerConnectionFactory();
-    pc = factory.createPeerConnection(
-        iceServers, appRtcClient.pcConstraints(), pcObserver);
+
+    MediaConstraints pcConstraints = appRtcClient.pcConstraints();
+    pcConstraints.optional.add(
+        new MediaConstraints.KeyValuePair("RtpDataChannels", "true"));
+    pc = factory.createPeerConnection(iceServers, pcConstraints, pcObserver);
+
+    createDataChannelToRegressionTestBug2302(pc);  // See method comment.
 
     // Uncomment to get ALL WebRTC tracing and SENSITIVE libjingle logging.
     // NOTE: this _must_ happen while |factory| is alive!