feat: error message return from api (#235)

* feat(storage): error message retyrn from api

* feat: add comment for clarification

* fix: remove unknown error

Co-authored-by: Tres Seaver <tseaver@palladion.com>
Co-authored-by: Frank Natividad <frankyn@users.noreply.github.com>

google/cloud/storage/blob.py

@@ -3427,7 +3427,13 @@ def _raise_from_invalid_response(error):
              to the failed status code
     """
     response = error.response
-    error_message = str(error)
+
+    # The 'response.text' gives the actual reason of error, where 'error' gives
+    # the message of expected status code.
+    if response.text:
+        error_message = response.text + ": " + str(error)
+    else:
+        error_message = str(error)
 
     message = u"{method} {url}: {error}".format(
         method=response.request.method, url=response.request.url, error=error_message

tests/unit/test_blob.py

@@ -4356,14 +4356,15 @@ def _call_fut(error):
 
         return _raise_from_invalid_response(error)
 
-    def _helper(self, message, code=http_client.BAD_REQUEST, args=()):
+    def _helper(self, message, code=http_client.BAD_REQUEST, reason=None, args=()):
         import requests
 
         from google.resumable_media import InvalidResponse
         from google.api_core import exceptions
 
         response = requests.Response()
         response.request = requests.Request("GET", "http://example.com").prepare()
+        response._content = reason
         response.status_code = code
         error = InvalidResponse(response, message, *args)
 
@@ -4381,9 +4382,14 @@ def test_default(self):
 
     def test_w_206_and_args(self):
         message = "Failure"
+        reason = b"Not available"
         args = ("one", "two")
-        exc_info = self._helper(message, code=http_client.PARTIAL_CONTENT, args=args)
-        expected = "GET http://example.com/: {}".format((message,) + args)
+        exc_info = self._helper(
+            message, code=http_client.PARTIAL_CONTENT, reason=reason, args=args
+        )
+        expected = "GET http://example.com/: {}: {}".format(
+            reason.decode("utf-8"), (message,) + args
+        )
         self.assertEqual(exc_info.exception.message, expected)
         self.assertEqual(exc_info.exception.errors, [])