Fix md5 hash logic. Make it order agnostic. (#640)

Co-authored-by: Martin Durant <martindurant@users.noreply.github.com>

gcsfs/checkers.py

@@ -46,7 +46,7 @@ def validate_headers(self, headers):
             dig = [
                 bit.split("=")[1]
                 for bit in headers["X-Goog-Hash"].split(",")
-                if bit.split("=")[0] == "md5"
+                if bit and bit.strip().startswith("md5=")
             ]
             if dig:
                 if b64encode(self.md.digest()).decode().rstrip("=") != dig[0]:

gcsfs/tests/test_checkers.py

@@ -8,7 +8,6 @@
 
 
 def google_response_from_data(expected_data: bytes, actual_data=None):
-
     actual_data = actual_data or expected_data
     checksum = md5(actual_data)
     checksum_b64 = base64.b64encode(checksum.digest()).decode("UTF-8")
@@ -21,7 +20,29 @@ class response:
         content_length = len(actual_data)
         headers = {"X-Goog-Hash": f"md5={checksum_b64}"}
         if crcmod is not None:
-            headers["X-Goog-Hash"] += f",crc32c={crc}"
+            headers["X-Goog-Hash"] += f", crc32c={crc}"
+
+    return response
+
+
+def google_response_from_data_with_reverse_header_order(
+    expected_data: bytes, actual_data=None
+):
+    actual_data = actual_data or expected_data
+    checksum = md5(actual_data)
+    checksum_b64 = base64.b64encode(checksum.digest()).decode("UTF-8")
+    if crcmod is not None:
+        checksum = crcmod.Crc(0x11EDC6F41, initCrc=0, xorOut=0xFFFFFFFF)
+        checksum.update(actual_data)
+        crc = base64.b64encode(checksum.digest()).decode()
+
+    class response:
+        content_length = len(actual_data)
+        headers = {}
+        if crcmod is not None:
+            headers["X-Goog-Hash"] = f"crc32c={crc}, md5={checksum_b64}"
+        else:
+            headers["X-Goog-Hash"] = f"md5={checksum_b64}"
 
     return response
 
@@ -73,6 +94,30 @@ def test_validate_headers(checker, data, actual_data, raises):
         checker.validate_headers(response.headers)
 
 
+params = [
+    (MD5Checker(), b"hello world", b"different checksum", (ChecksumError,)),
+    (MD5Checker(), b"hello world", b"hello world", ()),
+]
+
+if crcmod is not None:
+    params.append(
+        (Crc32cChecker(), b"hello world", b"different checksum", (ChecksumError,))
+    )
+    params.append((Crc32cChecker(), b"hello world", b"hello world", ()))
+
+
+@pytest.mark.parametrize("checker, data, actual_data, raises", params)
+def test_validate_headers_with_reverse_order(checker, data, actual_data, raises):
+    response = google_response_from_data_with_reverse_header_order(actual_data)
+    checker.update(data)
+
+    if raises:
+        with pytest.raises(raises):
+            checker.validate_headers(response.headers)
+    else:
+        checker.validate_headers(response.headers)
+
+
 params = [
     (MD5Checker(), b"hello world", b"different checksum", (ChecksumError,)),
     (MD5Checker(), b"hello world", b"hello world", ()),