Add a unit test for receiving 'finish' message after channel close

After the input channel is closed, the messages that were previously
written to the fd should still be readable. However, in some cases, if
the fd is closed with data in the fd's buffer, the data may be
discarded. This is confirmed by the attached unit test.

Add an explanation of this to the InputChannel implementation, so that
this behaviour is documented.

Bug: 376713684
Test: TEST=libinput_tests; m $TEST && adb sync data && adb shell -t /data/nativetest64/$TEST/$TEST --gtest_filter="*ReceiveAfterClose*" --gtest_repeat=100000 --gtest_break_on_failure
Test: TEST=libinput_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST --gtest_filter="*ReceiveAfterClose*" --gtest_repeat=100000 --gtest_break_on_failure
Flag: TEST_ONLY
Change-Id: I67a6a6432c4756283c8f2cca3c01210a3bcdb42e

Author: vishniakou

include/input/InputTransport.h

@@ -454,4 +454,6 @@ class InputPublisher {
     InputVerifier mInputVerifier;
 };
 
+std::ostream& operator<<(std::ostream& out, const InputMessage& msg);
+
 } // namespace android

libs/input/InputConsumerNoResampling.cpp

@@ -171,11 +171,6 @@ InputMessage createTimelineMessage(int32_t inputEventId, nsecs_t gpuCompletedTim
     return msg;
 }
 
-std::ostream& operator<<(std::ostream& out, const InputMessage& msg) {
-    out << ftl::enum_string(msg.header.type);
-    return out;
-}
-
 } // namespace
 
 // --- InputConsumerNoResampling ---

libs/input/InputTransport.cpp

@@ -436,16 +436,29 @@ android::base::Result<InputMessage> InputChannel::receiveMessage() {
         if (error == EAGAIN || error == EWOULDBLOCK) {
             return android::base::Error(WOULD_BLOCK);
         }
-        if (error == EPIPE || error == ENOTCONN || error == ECONNREFUSED) {
-            return android::base::Error(DEAD_OBJECT);
+        if (error == EPIPE) {
+            return android::base::ResultError("Got EPIPE", DEAD_OBJECT);
+        }
+        if (error == ENOTCONN) {
+            return android::base::ResultError("Got ENOTCONN", DEAD_OBJECT);
+        }
+        if (error == ECONNREFUSED) {
+            return android::base::ResultError("Got ECONNREFUSED", DEAD_OBJECT);
+        }
+        if (error == ECONNRESET) {
+            // This means that the client has closed the channel while there was
+            // still some data in the buffer. In most cases, subsequent reads
+            // would result in more data. However, that is not guaranteed, so we
+            // should not return WOULD_BLOCK here to try again.
+            return android::base::ResultError("Got ECONNRESET", DEAD_OBJECT);
         }
         return android::base::Error(-error);
     }
 
     if (nRead == 0) { // check for EOF
-        ALOGD_IF(DEBUG_CHANNEL_MESSAGES,
-                 "channel '%s' ~ receive message failed because peer was closed", name.c_str());
-        return android::base::Error(DEAD_OBJECT);
+        LOG_IF(INFO, DEBUG_CHANNEL_MESSAGES)
+                << "channel '" << name << "' ~ receive message failed because peer was closed";
+        return android::base::ResultError("::recv returned 0", DEAD_OBJECT);
     }
 
     if (!msg.isValid(nRead)) {
@@ -766,4 +779,9 @@ android::base::Result<InputPublisher::ConsumerResponse> InputPublisher::receiveC
     return android::base::Error(UNKNOWN_ERROR);
 }
 
+std::ostream& operator<<(std::ostream& out, const InputMessage& msg) {
+    out << ftl::enum_string(msg.header.type);
+    return out;
+}
+
 } // namespace android

libs/input/tests/InputChannel_test.cpp

@@ -20,6 +20,7 @@
 #include <time.h>
 #include <errno.h>
 
+#include <android-base/logging.h>
 #include <binder/Binder.h>
 #include <binder/Parcel.h>
 #include <gtest/gtest.h>
@@ -43,6 +44,39 @@ bool operator==(const InputChannel& left, const InputChannel& right) {
     return left.getName() == right.getName() &&
             left.getConnectionToken() == right.getConnectionToken() && lhs.st_ino == rhs.st_ino;
 }
+
+/**
+ * Read a message from the provided channel. Read will continue until there's data, so only call
+ * this if there's data in the channel, or it's closed. If there's no data, this will loop forever.
+ */
+android::base::Result<InputMessage> readMessage(InputChannel& channel) {
+    while (true) {
+        // Keep reading until we get something other than 'WOULD_BLOCK'
+        android::base::Result<InputMessage> result = channel.receiveMessage();
+        if (!result.ok() && result.error().code() == WOULD_BLOCK) {
+            // The data is not available yet.
+            continue; // try again
+        }
+        return result;
+    }
+}
+
+InputMessage createFinishedMessage(uint32_t seq) {
+    InputMessage finish{};
+    finish.header.type = InputMessage::Type::FINISHED;
+    finish.header.seq = seq;
+    finish.body.finished.handled = true;
+    return finish;
+}
+
+InputMessage createKeyMessage(uint32_t seq) {
+    InputMessage key{};
+    key.header.type = InputMessage::Type::KEY;
+    key.header.seq = seq;
+    key.body.key.action = AKEY_EVENT_ACTION_DOWN;
+    return key;
+}
+
 } // namespace
 
 class InputChannelTest : public testing::Test {
@@ -227,6 +261,120 @@ TEST_F(InputChannelTest, SendAndReceive_MotionClassification) {
     }
 }
 
+/**
+ * In this test, server writes 3 key events to the client. The client, upon receiving the first key,
+ * sends a "finished" signal back to server, and then closes the fd.
+ *
+ * Next, we check what the server receives.
+ *
+ * In most cases, the server will receive the finish event, and then an 'fd closed' event.
+ *
+ * However, sometimes, the 'finish' event will not be delivered to the server. This is communicated
+ * to the server via 'ECONNRESET', which the InputChannel converts into DEAD_OBJECT.
+ *
+ * The server needs to be aware of this behaviour and correctly clean up any state associated with
+ * the  client, even if the client did not end up finishing some of the messages.
+ *
+ * This test is written to expose a behaviour on the linux side - occasionally, the
+ * last events written to the fd by the consumer are not delivered to the server.
+ *
+ * When tested on 2025 hardware, ECONNRESET was received  approximately 1 out of 40 tries.
+ * In vast majority (~ 29999 / 30000) of cases, after receiving ECONNRESET, the server could still
+ * read the client data after receiving ECONNRESET.
+ */
+TEST_F(InputChannelTest, ReceiveAfterCloseMultiThreaded) {
+    std::unique_ptr<InputChannel> serverChannel, clientChannel;
+    status_t result =
+            InputChannel::openInputChannelPair("channel name", serverChannel, clientChannel);
+    ASSERT_EQ(OK, result) << "should have successfully opened a channel pair";
+
+    // Sender / publisher: publish 3 keys
+    InputMessage key1 = createKeyMessage(/*seq=*/1);
+    serverChannel->sendMessage(&key1);
+    // The client should close the fd after it reads this one, but we will send 2 more here.
+    InputMessage key2 = createKeyMessage(/*seq=*/2);
+    serverChannel->sendMessage(&key2);
+    InputMessage key3 = createKeyMessage(/*seq=*/3);
+    serverChannel->sendMessage(&key3);
+
+    std::thread consumer = std::thread([clientChannel = std::move(clientChannel)]() mutable {
+        // Read the first key
+        android::base::Result<InputMessage> firstKey = readMessage(*clientChannel);
+        if (!firstKey.ok()) {
+            FAIL() << "Did not receive the first key";
+        }
+
+        // Send finish
+        const InputMessage finish = createFinishedMessage(firstKey->header.seq);
+        clientChannel->sendMessage(&finish);
+        // Now close the fd
+        clientChannel.reset();
+    });
+
+    // Now try to read the finish message, even though client closed the fd
+    android::base::Result<InputMessage> response = readMessage(*serverChannel);
+    consumer.join();
+    if (response.ok()) {
+        ASSERT_EQ(response->header.type, InputMessage::Type::FINISHED);
+    } else {
+        // It's possible that after the client closes the fd, server will receive ECONNRESET.
+        // In those situations, this error code will be translated into DEAD_OBJECT by the
+        // InputChannel.
+        ASSERT_EQ(response.error().code(), DEAD_OBJECT);
+        // In most cases, subsequent attempts to read the client channel at this
+        // point would succeed. However, for simplicity, we exit here (since
+        // it's not guaranteed).
+        return;
+    }
+
+    // There should not be any more events from the client, since the client closed fd after the
+    // first key.
+    android::base::Result<InputMessage> noEvent = serverChannel->receiveMessage();
+    ASSERT_FALSE(noEvent.ok()) << "Got event " << *noEvent;
+}
+
+/**
+ * Similar test as above, but single-threaded.
+ */
+TEST_F(InputChannelTest, ReceiveAfterCloseSingleThreaded) {
+    std::unique_ptr<InputChannel> serverChannel, clientChannel;
+    status_t result =
+            InputChannel::openInputChannelPair("channel name", serverChannel, clientChannel);
+    ASSERT_EQ(OK, result) << "should have successfully opened a channel pair";
+
+    // Sender / publisher: publish 3 keys
+    InputMessage key1 = createKeyMessage(/*seq=*/1);
+    serverChannel->sendMessage(&key1);
+    // The client should close the fd after it reads this one, but we will send 2 more here.
+    InputMessage key2 = createKeyMessage(/*seq=*/2);
+    serverChannel->sendMessage(&key2);
+    InputMessage key3 = createKeyMessage(/*seq=*/3);
+    serverChannel->sendMessage(&key3);
+
+    // Read the first key
+    android::base::Result<InputMessage> firstKey = readMessage(*clientChannel);
+    if (!firstKey.ok()) {
+        FAIL() << "Did not receive the first key";
+    }
+
+    // Send finish
+    const InputMessage finish = createFinishedMessage(firstKey->header.seq);
+    clientChannel->sendMessage(&finish);
+    // Now close the fd
+    clientChannel.reset();
+
+    // Now try to read the finish message, even though client closed the fd
+    android::base::Result<InputMessage> response = readMessage(*serverChannel);
+    ASSERT_FALSE(response.ok());
+    ASSERT_EQ(response.error().code(), DEAD_OBJECT);
+
+    // We can still read the finish event (but in practice, the expectation is that the server will
+    // not be doing this after getting DEAD_OBJECT).
+    android::base::Result<InputMessage> finishEvent = serverChannel->receiveMessage();
+    ASSERT_TRUE(finishEvent.ok());
+    ASSERT_EQ(finishEvent->header.type, InputMessage::Type::FINISHED);
+}
+
 TEST_F(InputChannelTest, DuplicateChannelAndAssertEqual) {
     std::unique_ptr<InputChannel> serverChannel, clientChannel;