filters.py: Make decompression robust towards decompressed input

tests/unit/test_filters.py

@@ -298,6 +298,18 @@ def test_decode_response_deflate():
     assert decoded_response["headers"]["content-length"] == [str(len(body))]
 
 
+def test_decode_response_deflate_already_decompressed():
+    body = b"deflate message"
+    gzip_response = {
+        "body": {"string": body},
+        "headers": {
+            "content-encoding": ["deflate"],
+        },
+    }
+    decoded_response = decode_response(gzip_response)
+    assert decoded_response["body"]["string"] == body
+
+
 def test_decode_response_gzip():
     body = b"gzip message"
 
@@ -325,3 +337,15 @@ def test_decode_response_gzip():
     decoded_response = decode_response(gzip_response)
     assert decoded_response["body"]["string"] == body
     assert decoded_response["headers"]["content-length"] == [str(len(body))]
+
+
+def test_decode_response_gzip_already_decompressed():
+    body = b"gzip message"
+    gzip_response = {
+        "body": {"string": body},
+        "headers": {
+            "content-encoding": ["gzip"],
+        },
+    }
+    decoded_response = decode_response(gzip_response)
+    assert decoded_response["body"]["string"] == body

vcr/filters.py

@@ -153,9 +153,15 @@ def decode_response(response):
         if not body:
             return ""
         if encoding == "gzip":
-            return zlib.decompress(body, zlib.MAX_WBITS | 16)
+            try:
+                return zlib.decompress(body, zlib.MAX_WBITS | 16)
+            except zlib.error:
+                return body  # assumes that the data was already decompressed
         else:  # encoding == 'deflate'
-            return zlib.decompress(body)
+            try:
+                return zlib.decompress(body)
+            except zlib.error:
+                return body  # assumes that the data was already decompressed
 
     # Deepcopy here in case `headers` contain objects that could
     # be mutated by a shallow copy and corrupt the real response.