websockets: A progressive masker.

netlib/websockets.py

@@ -35,21 +35,25 @@ OPCODE = utils.BiDi(
 )
 
 
-def apply_mask(message, masking_key):
+class Masker:
     """
-    Data sent from the server must be masked to prevent malicious clients
-    from sending data over the wire in predictable patterns
+        Data sent from the server must be masked to prevent malicious clients
+        from sending data over the wire in predictable patterns
 
-    This method both encodes and decodes strings with the provided mask
-
-    Servers do not have to mask data they send to the client.
-    https://tools.ietf.org/html/rfc6455#section-5.3
+        Servers do not have to mask data they send to the client.
+        https://tools.ietf.org/html/rfc6455#section-5.3
     """
-    masks = [utils.bytes_to_int(byte) for byte in masking_key]
-    result = ""
-    for char in message:
-        result += chr(ord(char) ^ masks[len(result) % 4])
-    return result
+    def __init__(self, key):
+        self.key = key
+        self.masks = [utils.bytes_to_int(byte) for byte in key]
+        self.offset = 0
+
+    def __call__(self, data):
+        result = ""
+        for c in data:
+            result += chr(ord(c) ^ self.masks[self.offset % 4])
+            self.offset += 1
+        return result
 
 
 def client_handshake_headers(key=None, version=VERSION):
@@ -324,7 +328,7 @@ class Frame(object):
         """
         b = self.header.to_bytes()
         if self.header.masking_key:
-            b += apply_mask(self.payload, self.header.masking_key)
+            b += Masker(self.header.masking_key)(self.payload)
         else:
             b += self.payload
         return b
@@ -345,7 +349,7 @@ class Frame(object):
         payload = fp.read(header.payload_length)
 
         if header.mask == 1 and header.masking_key:
-            payload = apply_mask(payload, header.masking_key)
+            payload = Masker(header.masking_key)(payload)
 
         return cls(
             payload,

test/test_websockets.py

@@ -232,3 +232,19 @@ class TestFrame:
     def test_human_readable(self):
         f = websockets.Frame()
         assert f.human_readable()
+
+
+def test_masker():
+    tests = [
+        ["a"],
+        ["four"],
+        ["fourf"],
+        ["fourfive"],
+        ["a", "aasdfasdfa", "asdf"],
+        ["a"*50, "aasdfasdfa", "asdf"],
+    ]
+    for i in tests:
+        m = websockets.Masker("abcd")
+        data = "".join([m(t) for t in i])
+        data2 = websockets.Masker("abcd")(data)
+        assert data2 == "".join(i)