Ensure Content-Length is a string.

requests/models.py

@@ -121,7 +121,7 @@ class RequestEncodingMixin(object):
                 fp = StringIO(fp)
             if isinstance(fp, bytes):
                 fp = BytesIO(fp)
-            
+
             if ft:
                 new_v = (fn, fp.read(), ft)
             else:
@@ -346,7 +346,7 @@ class PreparedRequest(RequestEncodingMixin, RequestHooksMixin):
         ])
 
         try:
-            length = super_len(data)
+            length = str(super_len(data))
         except (TypeError, AttributeError):
             length = False
 

test_requests.py

@@ -9,6 +9,12 @@ import unittest
 
 import requests
 from requests.auth import HTTPDigestAuth
+from requests.compat import str
+
+try:
+    import StringIO
+except ImportError:
+    import io as StringIO
 
 HTTPBIN = os.environ.get('HTTPBIN_URL', 'http://httpbin.org/')
 
@@ -131,8 +137,6 @@ class RequestsTestCase(unittest.TestCase):
         self.assertEqual(r.status_code, 200)
 
     def test_BASICAUTH_TUPLE_HTTP_200_OK_GET(self):
-
-
         auth = ('user', 'pass')
         url = httpbin('basic-auth', 'user', 'pass')
 
@@ -264,6 +268,11 @@ class RequestsTestCase(unittest.TestCase):
         self.assertEqual(r.status_code, 200)
         self.assertTrue(b"text/py-content-type" in r.request.body)
 
+    def test_content_length_is_string_for_file_objects(self):
+        r = requests.Request(url='http://httpbin.org/post',
+                             data=StringIO.StringIO('abc')).prepare()
+        self.assertTrue(type(r.headers['Content-Length']) == str)
+
 
 if __name__ == '__main__':
     unittest.main()