fix: allow space in checksum header (#170)

The current checksum logic only allowed checksum
 headers in the format "crc32c=hash1,md5=hash2",
 but GCP may actually return them with a space
 in-between as "crc32c=hash1, md5=hash2".

Resolves #169

Co-authored-by: Christopher Wilcox <crwilcox@google.com>

google/resumable_media/_helpers.py

@@ -317,7 +317,8 @@ def _parse_checksum_header(header_value, response, checksum_label):
     matches = []
     for checksum in header_value.split(u","):
         name, value = checksum.split(u"=", 1)
-        if name == checksum_label:
+        # Official docs say "," is the separator, but real-world responses have encountered ", "
+        if name.lstrip() == checksum_label:
             matches.append(value)
 
     if len(matches) == 0:

tests/unit/test__helpers.py

@@ -311,11 +311,12 @@ def test__DoNothingHash():
 
 
 class Test__get_expected_checksum(object):
+    @pytest.mark.parametrize("template", [u"crc32c={},md5={}", u"crc32c={}, md5={}"])
     @pytest.mark.parametrize("checksum", ["md5", "crc32c"])
     @mock.patch("google.resumable_media._helpers._LOGGER")
-    def test__w_header_present(self, _LOGGER, checksum):
+    def test__w_header_present(self, _LOGGER, template, checksum):
         checksums = {"md5": u"b2twdXNodGhpc2J1dHRvbg==", "crc32c": u"3q2+7w=="}
-        header_value = u"crc32c={},md5={}".format(checksums["crc32c"], checksums["md5"])
+        header_value = template.format(checksums["crc32c"], checksums["md5"])
         headers = {_helpers._HASH_HEADER: header_value}
         response = _mock_response(headers=headers)