fix: fix processing lambda container response if nothing returned (#5771

)

* fix: fix processing lambda container response if nothing returned

* add integration test case

samcli/local/docker/container.py

@@ -331,7 +331,7 @@ def wait_for_http_response(self, name, event, stdout) -> str:
             data=event.encode("utf-8"),
             timeout=(self.RAPID_CONNECTION_TIMEOUT, None),
         )
-        return json.dumps(json.loads(resp.content), ensure_ascii=False)
+        return json.dumps(json.loads(resp.content), ensure_ascii=False) if resp.content else ""
 
     def wait_for_result(self, full_path, event, stdout, stderr, start_timer=None):
         # NOTE(sriram-mv): Let logging happen in its own thread, so that a http request can be sent.

tests/integration/local/invoke/test_integrations_cli.py

@@ -47,6 +47,21 @@ def test_invoke_returncode_is_zero(self):
 
         self.assertEqual(process.returncode, 0)
 
+    @pytest.mark.flaky(reruns=3)
+    def test_invoke_no_response_returncode_is_zero(self):
+        command_list = InvokeIntegBase.get_command_list(
+            "NoResponseServerlessFunction", template_path=self.template_path, event_path=self.event_path
+        )
+
+        process = Popen(command_list, stdout=PIPE)
+        try:
+            process.communicate(timeout=TIMEOUT)
+        except TimeoutExpired:
+            process.kill()
+            raise
+
+        self.assertEqual(process.returncode, 0)
+
     # https://github.com/aws/aws-sam-cli/issues/2494
     @pytest.mark.flaky(reruns=3)
     def test_invoke_with_utf8_event(self):

tests/integration/testdata/invoke/main.py

@@ -56,3 +56,7 @@ def execute_git(event, context):
     assert return_code == 0
 
     return "git init passed"
+
+
+def no_response(event, context):
+    print("lambda called")

tests/integration/testdata/invoke/template.yml

@@ -35,6 +35,14 @@ Resources:
       CodeUri: .
       Timeout: 600
 
+  NoResponseServerlessFunction:
+    Type: AWS::Serverless::Function
+    Properties:
+      Handler: main.no_response
+      Runtime: python3.9
+      CodeUri: .
+      Timeout: 600
+
   HelloWorldLambdaFunction:
     Type: AWS::Lambda::Function
     Properties: