Add new API to support config replace (#125)

Why I did it
Sonic host services need to support GCU config replace operation.

How I did it
Add new API for config replace

How did I verify it
Run unit test

host_modules/gcu.py

@@ -39,6 +39,36 @@ def apply_patch_yang(self, patch_text):
                     break
         return result.returncode, msg
 
+    @host_service.method(host_service.bus_name(MOD_NAME), in_signature='s', out_signature='is')
+    def replace_db(self, patch_text):
+        input_bytes = (patch_text + '\n').encode('utf-8')
+        cmd = ['/usr/local/bin/config', 'replace', '-f', 'CONFIGDB', '/dev/stdin']
+
+        result = subprocess.run(cmd, input=input_bytes, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+        msg = ''
+        if result.returncode:
+            lines = result.stderr.decode().split('\n')
+            for line in lines:
+                if 'Error' in line:
+                    msg = line
+                    break
+        return result.returncode, msg
+
+    @host_service.method(host_service.bus_name(MOD_NAME), in_signature='s', out_signature='is')
+    def replace_yang(self, patch_text):
+        input_bytes = (patch_text + '\n').encode('utf-8')
+        cmd = ['/usr/local/bin/config', 'replace', '-f', 'SONICYANG', '/dev/stdin']
+
+        result = subprocess.run(cmd, input=input_bytes, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+        msg = ''
+        if result.returncode:
+            lines = result.stderr.decode().split('\n')
+            for line in lines:
+                if 'Error' in line:
+                    msg = line
+                    break
+        return result.returncode, msg
+
     @host_service.method(host_service.bus_name(MOD_NAME), in_signature='s', out_signature='is')
     def create_checkpoint(self, checkpoint_file):
 

tests/host_modules/gcu_test.py

@@ -79,6 +79,80 @@ def test_apply_patch_yang(self, MockInit, MockBusName, MockSystemBus):
             assert ret == test_ret, "Return value is wrong"
             assert msg == "Error: this is the test message", "Return message is wrong"
 
+    @mock.patch("dbus.SystemBus")
+    @mock.patch("dbus.service.BusName")
+    @mock.patch("dbus.service.Object.__init__")
+    def test_replace_db(self, MockInit, MockBusName, MockSystemBus):
+        with mock.patch("subprocess.run") as mock_run:
+            res_mock = mock.Mock()
+            test_ret = 0
+            test_msg = b"Error: this is the test message\nHello world\n"
+            attrs = {"returncode": test_ret, "stderr": test_msg}
+            res_mock.configure_mock(**attrs)
+            mock_run.return_value = res_mock
+            patch_text = "{}"
+            gcu_stub = gcu.GCU(gcu.MOD_NAME)
+            ret, msg = gcu_stub.replace_db(patch_text)
+            call_args = mock_run.call_args[0][0]
+            assert "replace" in call_args
+            assert "CONFIGDB" in call_args
+            assert '/dev/stdin' in call_args
+            assert ret == test_ret, "Return value is wrong"
+            assert msg == "", "Return message is wrong"
+        with mock.patch("subprocess.run") as mock_run:
+            res_mock = mock.Mock()
+            test_ret = 1
+            test_msg = b"Error: this is the test message\nHello world\n"
+            attrs = {"returncode": test_ret, "stderr": test_msg}
+            res_mock.configure_mock(**attrs)
+            mock_run.return_value = res_mock
+            patch_text = "{}"
+            gcu_stub = gcu.GCU(gcu.MOD_NAME)
+            ret, msg = gcu_stub.replace_db(patch_text)
+            call_args = mock_run.call_args[0][0]
+            assert "replace" in call_args
+            assert "CONFIGDB" in call_args
+            assert '/dev/stdin' in call_args
+            assert ret == test_ret, "Return value is wrong"
+            assert msg == "Error: this is the test message", "Return message is wrong"
+
+    @mock.patch("dbus.SystemBus")
+    @mock.patch("dbus.service.BusName")
+    @mock.patch("dbus.service.Object.__init__")
+    def test_replace_yang(self, MockInit, MockBusName, MockSystemBus):
+        with mock.patch("subprocess.run") as mock_run:
+            res_mock = mock.Mock()
+            test_ret = 0
+            test_msg = b"Error: this is the test message\nHello world\n"
+            attrs = {"returncode": test_ret, "stderr": test_msg}
+            res_mock.configure_mock(**attrs)
+            mock_run.return_value = res_mock
+            patch_text = "{}"
+            gcu_stub = gcu.GCU(gcu.MOD_NAME)
+            ret, msg = gcu_stub.replace_yang(patch_text)
+            call_args = mock_run.call_args[0][0]
+            assert "replace" in call_args
+            assert "SONICYANG" in call_args
+            assert '/dev/stdin' in call_args
+            assert ret == test_ret, "Return value is wrong"
+            assert msg == "", "Return message is wrong"
+        with mock.patch("subprocess.run") as mock_run:
+            res_mock = mock.Mock()
+            test_ret = 1
+            test_msg = b"Error: this is the test message\nHello world\n"
+            attrs = {"returncode": test_ret, "stderr": test_msg}
+            res_mock.configure_mock(**attrs)
+            mock_run.return_value = res_mock
+            patch_text = "{}"
+            gcu_stub = gcu.GCU(gcu.MOD_NAME)
+            ret, msg = gcu_stub.replace_yang(patch_text)
+            call_args = mock_run.call_args[0][0]
+            assert "replace" in call_args
+            assert "SONICYANG" in call_args
+            assert '/dev/stdin' in call_args
+            assert ret == test_ret, "Return value is wrong"
+            assert msg == "Error: this is the test message", "Return message is wrong"
+
     @mock.patch("dbus.SystemBus")
     @mock.patch("dbus.service.BusName")
     @mock.patch("dbus.service.Object.__init__")