diff --git a/trunk/src/utest/srs_utest_protostack.cpp b/trunk/src/utest/srs_utest_protostack.cpp
index f0f2cd200..3c26e3452 100644
--- a/trunk/src/utest/srs_utest_protostack.cpp
+++ b/trunk/src/utest/srs_utest_protostack.cpp
@@ -22,7 +22,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 #include <srs_utest_protostack.hpp>
 
-using namespace std;
+#include <srs_utest_protocol.hpp>
 
 #include <srs_kernel_error.hpp>
 #include <srs_core_autofree.hpp>
@@ -36,6 +36,8 @@ using namespace std;
 #include <srs_service_http_conn.hpp>
 #include <srs_kernel_buffer.hpp>
 
+using namespace std;
+
 class MockErrorPacket : public SrsPacket
 {
 protected:
@@ -75,3 +77,75 @@ VOID TEST(ProtoStackTest, PacketEncode)
     }
 }
 
+VOID TEST(ProtoStackTest, ManualFlush)
+{
+    srs_error_t err;
+
+    if (true) {
+        MockBufferIO io;
+        SrsProtocol p(&io);
+
+        // Always response ACK message.
+        HELPER_EXPECT_SUCCESS(p.set_in_window_ack_size(1));
+
+        // Default is auto response.
+        HELPER_EXPECT_SUCCESS(p.response_acknowledgement_message());
+        EXPECT_EQ(12+4, io.out_buffer.length());
+    }
+
+    if (true) {
+        MockBufferIO io;
+        SrsProtocol p(&io);
+
+        // Always response ACK message.
+        HELPER_EXPECT_SUCCESS(p.set_in_window_ack_size(1));
+
+        p.set_auto_response(true);
+        HELPER_EXPECT_SUCCESS(p.response_acknowledgement_message());
+        EXPECT_EQ(12+4, io.out_buffer.length());
+    }
+
+    if (true) {
+        MockBufferIO io;
+        SrsProtocol p(&io);
+
+        // Always response ACK message.
+        HELPER_EXPECT_SUCCESS(p.set_in_window_ack_size(1));
+
+        // When not auto response, need to flush it manually.
+        p.set_auto_response(false);
+        HELPER_EXPECT_SUCCESS(p.response_acknowledgement_message());
+        EXPECT_EQ(0, io.out_buffer.length());
+
+        HELPER_EXPECT_SUCCESS(p.manual_response_flush());
+        EXPECT_EQ(12+4, io.out_buffer.length());
+    }
+
+    if (true) {
+        MockBufferIO io;
+        SrsProtocol p(&io);
+
+        // Always response ACK message.
+        HELPER_EXPECT_SUCCESS(p.set_in_window_ack_size(1));
+
+        HELPER_EXPECT_SUCCESS(p.response_ping_message(1024));
+        EXPECT_EQ(12+6, io.out_buffer.length());
+    }
+
+    if (true) {
+        MockBufferIO io;
+        SrsProtocol p(&io);
+
+        // Always response ACK message.
+        HELPER_EXPECT_SUCCESS(p.set_in_window_ack_size(1));
+
+        // When not auto response, need to flush it manually.
+        p.set_auto_response(false);
+        HELPER_EXPECT_SUCCESS(p.response_ping_message(1024));
+        EXPECT_EQ(0, io.out_buffer.length());
+
+        HELPER_EXPECT_SUCCESS(p.manual_response_flush());
+        EXPECT_EQ(12+6, io.out_buffer.length());
+    }
+}
+