Implement BasicAuth decode classmethod.

aiohttp/helpers.py

@@ -2,6 +2,7 @@
 
 import asyncio
 import base64
+import binascii
 import datetime
 import functools
 import io
@@ -42,6 +43,27 @@ def __new__(cls, login, password='', encoding='latin1'):
 
         return super().__new__(cls, login, password, encoding)
 
+    @classmethod
+    def decode(cls, auth_header, encoding='latin1'):
+        """Create a :class:`BasicAuth` object from an ``Authorization`` HTTP
+        header."""
+        split = auth_header.strip().split(' ')
+        if len(split) == 2:
+            if split[0].strip().lower() != 'basic':
+                raise ValueError('Unknown authorization method %s' % split[0])
+            to_decode = split[1]
+        else:
+            raise ValueError('Could not parse authorization header.')
+
+        try:
+            username, _, password = base64.b64decode(
+                to_decode.encode('ascii')
+            ).decode(encoding).partition(':')
+        except binascii.Error:
+            raise ValueError('Invalid base64 encoding.')
+
+        return cls(username, password, encoding=encoding)
+
     def encode(self):
         """Encode credentials."""
         creds = ('%s:%s' % (self.login, self.password)).encode(self.encoding)

docs/client_reference.rst

@@ -1291,6 +1291,16 @@ BasicAuth
    e.g. *auth* parameter for :meth:`ClientSession.request`.
 
 
+   .. classmethod:: decode(auth_header, encoding='latin1')
+
+      Decode HTTP basic authentication credentials.
+
+      :param str auth_header:  The ``Authorization`` header to decode.
+      :param str encoding: (optional) encoding ('latin1' by default)
+
+      :return:  decoded authentication data, :class:`BasicAuth`.
+
+
    .. method:: encode()
 
       Encode credentials into string suitable for ``Authorization``

tests/test_helpers.py

@@ -71,6 +71,27 @@ def test_basic_auth4():
     assert auth.encode() == 'Basic bmtpbTpwd2Q='
 
 
+def test_basic_auth_decode():
+    auth = helpers.BasicAuth.decode('Basic bmtpbTpwd2Q=')
+    assert auth.login == 'nkim'
+    assert auth.password == 'pwd'
+
+
+def test_basic_auth_invalid():
+    with pytest.raises(ValueError):
+        helpers.BasicAuth.decode('bmtpbTpwd2Q=')
+
+
+def test_basic_auth_decode_not_basic():
+    with pytest.raises(ValueError):
+        helpers.BasicAuth.decode('Complex bmtpbTpwd2Q=')
+
+
+def test_basic_auth_decode_bad_base64():
+    with pytest.raises(ValueError):
+        helpers.BasicAuth.decode('Basic bmtpbTpwd2Q')
+
+
 def test_invalid_formdata_params():
     with pytest.raises(TypeError):
         helpers.FormData('asdasf')