remove 'Content-Encoding' header when returning responses

scrapy_zyte_api/responses.py

@@ -8,6 +8,14 @@
 
 
 class ZyteAPIMixin:
+
+    REMOVE_HEADERS = {
+        # Zyte API already decompresses the HTTP Response Body. Scrapy's
+        # HttpCompressionMiddleware will error out when it attempts to
+        # decompress an already decompressed body based on this header.
+        "content-encoding"
+    }
+
     def __init__(self, *args, zyte_api_response: Dict = None, **kwargs):
         super().__init__(*args, **kwargs)
         self._zyte_api_response = zyte_api_response
@@ -27,11 +35,15 @@ def zyte_api_response(self) -> Optional[Dict]:
         """
         return self._zyte_api_response
 
-    @staticmethod
-    def _prepare_headers(init_headers: Optional[List[Dict[str, str]]]):
+    @classmethod
+    def _prepare_headers(cls, init_headers: Optional[List[Dict[str, str]]]):
         if not init_headers:
             return None
-        return {h["name"]: h["value"] for h in init_headers}
+        return {
+            h["name"]: h["value"]
+            for h in init_headers
+            if h["name"].lower() not in cls.REMOVE_HEADERS
+        }
 
 
 class ZyteAPITextResponse(ZyteAPIMixin, TextResponse):

tests/test_responses.py

@@ -135,3 +135,32 @@ def test_non_utf8_response():
     response = ZyteAPITextResponse.from_api_response(sample_zyte_api_response)
     assert response.text == content
     assert response.encoding == "utf-8"
+
+
+@pytest.mark.parametrize(
+    "api_response,cls",
+    [
+        (api_response_browser, ZyteAPITextResponse),
+        (api_response_body, ZyteAPIResponse),
+    ],
+)
+def test_response_headers_removal(api_response, cls):
+    """Headers like 'Content-Encoding' should be removed later in the response
+    instance returned to Scrapy.
+
+    However, it should still be present inside 'zyte_api_response.headers'.
+    """
+    additional_headers = [
+        {"name": "Content-Encoding", "value": "gzip"},
+        {"name": "X-Some-Other-Value", "value": "123"},
+    ]
+    raw_response = api_response()
+    raw_response["httpResponseHeaders"] = additional_headers
+
+    response = cls.from_api_response(raw_response)
+
+    assert response.headers == {b"X-Some-Other-Value": [b"123"]}
+    assert (
+        response.zyte_api_response["httpResponseHeaders"]
+        == raw_response["httpResponseHeaders"]
+    )