fix: avoid double encoding

Author: rubenfonseca

aws_lambda_powertools/event_handler/api_gateway.py

@@ -789,7 +789,10 @@ def build(self, event: ResponseEventT, cors: Optional[CORSConfig] = None) -> Dic
             logger.debug("Encoding bytes response with base64")
             self.response.base64_encoded = True
             self.response.body = base64.b64encode(self.response.body).decode()
-        elif self.response.is_json():
+
+        # We only apply the serializer when the content type is JSON and the
+        # body is not a str, to avoid double encoding
+        elif self.response.is_json() and not isinstance(self.response.body, str):
             self.response.body = self.serializer(self.response.body)
 
         # We only apply the serializer when the content type is JSON and the

tests/functional/event_handler/test_api_gateway.py

@@ -1482,7 +1482,7 @@ def get_lambda() -> Response:
     # THEN call the exception_handler
     assert result["statusCode"] == 500
     assert result["multiValueHeaders"]["Content-Type"] == [content_types.APPLICATION_JSON]
-    assert result["body"] == '"CUSTOM ERROR FORMAT"'
+    assert result["body"] == "CUSTOM ERROR FORMAT"
 
 
 def test_exception_handler_not_found():

tests/functional/event_handler/test_base_path.py

@@ -21,7 +21,7 @@ def handle():
 
     result = app(event, {})
     assert result["statusCode"] == 200
-    assert result["body"] == '""'
+    assert result["body"] == ""
 
 
 def test_base_path_api_gateway_http():
@@ -38,7 +38,7 @@ def handle():
 
     result = app(event, {})
     assert result["statusCode"] == 200
-    assert result["body"] == '""'
+    assert result["body"] == ""
 
 
 def test_base_path_alb():
@@ -53,7 +53,7 @@ def handle():
 
     result = app(event, {})
     assert result["statusCode"] == 200
-    assert result["body"] == '""'
+    assert result["body"] == ""
 
 
 def test_base_path_lambda_function_url():
@@ -70,7 +70,7 @@ def handle():
 
     result = app(event, {})
     assert result["statusCode"] == 200
-    assert result["body"] == '""'
+    assert result["body"] == ""
 
 
 def test_vpc_lattice():
@@ -85,7 +85,7 @@ def handle():
 
     result = app(event, {})
     assert result["statusCode"] == 200
-    assert result["body"] == '""'
+    assert result["body"] == ""
 
 
 def test_vpc_latticev2():
@@ -100,4 +100,4 @@ def handle():
 
     result = app(event, {})
     assert result["statusCode"] == 200
-    assert result["body"] == '""'
+    assert result["body"] == ""