4 files changed, 47 insertions, 23 deletions

diff --git a/src/android/net/util/FdEventsReader.java b/src/android/net/util/FdEventsReader.java
index 1380ea7..e82c69b 100644
--- a/src/android/net/util/FdEventsReader.java
+++ b/src/android/net/util/FdEventsReader.java
@@ -63,7 +63,6 @@ import java.io.IOException;
  * the Handler constructor argument is associated.
  *
  * @param <BufferType> the type of the buffer used to read data.
- * @hide
  */
 public abstract class FdEventsReader<BufferType> {
     private static final int FD_EVENTS = EVENT_INPUT | EVENT_ERROR;
@@ -93,27 +92,21 @@ public abstract class FdEventsReader<BufferType> {
     }
 
     /** Start this FdEventsReader. */
-    public void start() {
-        if (onCorrectThread()) {
-            createAndRegisterFd();
-        } else {
-            mHandler.post(() -> {
-                logError("start() called from off-thread", null);
-                createAndRegisterFd();
-            });
+    public boolean start() {
+        if (!onCorrectThread()) {
+            throw new IllegalStateException("start() called from off-thread");
         }
+
+        return createAndRegisterFd();
     }
 
     /** Stop this FdEventsReader and destroy the file descriptor. */
     public void stop() {
-        if (onCorrectThread()) {
-            unregisterAndDestroyFd();
-        } else {
-            mHandler.post(() -> {
-                logError("stop() called from off-thread", null);
-                unregisterAndDestroyFd();
-            });
+        if (!onCorrectThread()) {
+            throw new IllegalStateException("stop() called from off-thread");
         }
+
+        unregisterAndDestroyFd();
     }
 
     @NonNull
@@ -178,8 +171,8 @@ public abstract class FdEventsReader<BufferType> {
      */
     protected void onStop() {}
 
-    private void createAndRegisterFd() {
-        if (mFd != null) return;
+    private boolean createAndRegisterFd() {
+        if (mFd != null) return true;
 
         try {
             mFd = createFd();
@@ -189,7 +182,7 @@ public abstract class FdEventsReader<BufferType> {
             mFd = null;
         }
 
-        if (mFd == null) return;
+        if (mFd == null) return false;
 
         mQueue.addOnFileDescriptorEventListener(
                 mFd,
@@ -205,6 +198,7 @@ public abstract class FdEventsReader<BufferType> {
                     return FD_EVENTS;
                 });
         onStart();
+        return true;
     }
 
     private boolean isRunning() {
diff --git a/src/android/net/util/PacketReader.java b/src/android/net/util/PacketReader.java
index 4aec6b6..0be7187 100644
--- a/src/android/net/util/PacketReader.java
+++ b/src/android/net/util/PacketReader.java
@@ -28,8 +28,6 @@ import java.io.FileDescriptor;
  *
  * TODO: rename this class to something more correctly descriptive (something
  * like [or less horrible than] FdReadEventsHandler?).
- *
- * @hide
  */
 public abstract class PacketReader extends FdEventsReader<byte[]> {
 
diff --git a/tests/unit/src/android/net/ip/IpReachabilityMonitorTest.java b/tests/unit/src/android/net/ip/IpReachabilityMonitorTest.java
index 64b168a..428baac 100644
--- a/tests/unit/src/android/net/ip/IpReachabilityMonitorTest.java
+++ b/tests/unit/src/android/net/ip/IpReachabilityMonitorTest.java
@@ -62,6 +62,8 @@ public class IpReachabilityMonitorTest {
 
     @Test
     public void testNothing() {
-        IpReachabilityMonitor monitor = makeMonitor();
+        // make sure the unit test runs in the same thread with main looper.
+        // Otherwise, throwing IllegalStateException would cause test fails.
+        mHandler.post(() -> makeMonitor());
     }
 }
diff --git a/tests/unit/src/android/net/util/PacketReaderTest.java b/tests/unit/src/android/net/util/PacketReaderTest.java
index 289dcad..3947d15 100644
--- a/tests/unit/src/android/net/util/PacketReaderTest.java
+++ b/tests/unit/src/android/net/util/PacketReaderTest.java
@@ -24,6 +24,8 @@ import static android.system.OsConstants.SOCK_NONBLOCK;
 import static android.system.OsConstants.SOL_SOCKET;
 import static android.system.OsConstants.SO_SNDTIMEO;
 
+import static com.android.testutils.MiscAssertsKt.assertThrows;
+
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
@@ -182,7 +184,7 @@ public class PacketReaderTest {
         assertTrue(Arrays.equals(two, mLastRecvBuf));
         assertFalse(mStopped);
 
-        mReceiver.stop();
+        h.post(() -> mReceiver.stop());
         waitForActivity();
         assertEquals(2, mReceiver.numPacketsReceived());
         assertTrue(Arrays.equals(two, mLastRecvBuf));
@@ -208,4 +210,32 @@ public class PacketReaderTest {
             assertEquals(DEFAULT_RECV_BUF_SIZE, b.recvBufSize());
         }
     }
+
+    @Test
+    public void testStartingFromWrongThread() throws Exception {
+        final Handler h = mHandlerThread.getThreadHandler();
+        final PacketReader b = new NullPacketReader(h, DEFAULT_RECV_BUF_SIZE);
+        assertThrows(IllegalStateException.class, () -> b.start());
+    }
+
+    @Test
+    public void testStoppingFromWrongThread() throws Exception {
+        final Handler h = mHandlerThread.getThreadHandler();
+        final PacketReader b = new NullPacketReader(h, DEFAULT_RECV_BUF_SIZE);
+        assertThrows(IllegalStateException.class, () -> b.stop());
+    }
+
+    @Test
+    public void testSuccessToCreateSocket() throws Exception {
+        final Handler h = mHandlerThread.getThreadHandler();
+        final PacketReader b = new UdpLoopbackReader(h);
+        h.post(() -> assertTrue(b.start()));
+    }
+
+    @Test
+    public void testFailToCreateSocket() throws Exception {
+        final Handler h = mHandlerThread.getThreadHandler();
+        final PacketReader b = new NullPacketReader(h, DEFAULT_RECV_BUF_SIZE);
+        h.post(() -> assertFalse(b.start()));
+    }
 }