fix 400 errors on retries in _call (#380)

* fix 400 errors on retries in _call

The kwargs was being overwritten by ._get_args. If any retries are
needed, then on the second iteration datain will always be 'None'.  This
will cause uploading steps to return with exit code 400.

This commit fixes this bug by refactoring the _call method to minimize
the number of variabes in the scope.

Resolves #290

* rename to params for clarity

gcsfs/core.py

@@ -498,6 +498,27 @@ def _get_args(self, path, *args, **kwargs):
             kwargs["userProject"] = user_project
         return path, jsonin, datain, headers, kwargs
 
+    async def _request(self, method, path, *args, **kwargs):
+        await self._set_session()
+        self.maybe_refresh()
+        path, jsonin, datain, headers, params = self._get_args(path, *args, **kwargs)
+        async with self.session.request(
+            method=method,
+            url=path,
+            params=params,
+            json=jsonin,
+            headers=headers,
+            data=datain,
+            timeout=self.requests_timeout,
+        ) as r:
+
+            status = r.status
+            headers = r.headers
+            info = r.request_info  # for debug only
+            contents = await r.read()
+
+            return status, headers, info, contents
+
     async def _call(
         self, method, path, *args, json_out=False, info_out=False, **kwargs
     ):
@@ -507,26 +528,9 @@ async def _call(
             try:
                 if retry > 0:
                     await asyncio.sleep(min(random.random() + 2 ** (retry - 1), 32))
-                self.maybe_refresh()
-                path, jsonin, datain, headers, kwargs = self._get_args(
-                    path, *args, **kwargs
+                status, headers, info, contents = await self._request(
+                    method, path, *args, **kwargs
                 )
-                await self._set_session()
-                async with self.session.request(
-                    method=method,
-                    url=path,
-                    params=kwargs,
-                    json=jsonin,
-                    headers=headers,
-                    data=datain,
-                    timeout=self.requests_timeout,
-                ) as r:
-
-                    status = r.status
-                    headers = r.headers
-                    info = r.request_info  # for debug only
-                    contents = await r.read()
-
                 self.validate_response(status, contents, path, headers)
                 break
             except (HttpError, RequestException, GoogleAuthError, ChecksumError) as e: