Added draft for extensions implementation

extension.py

+from errors import HandshakeError
+
+
+class Extension(object):
+    rsv1 = False
+    rsv2 = False
+    rsv3 = False
+    opcodes = []
+    parameters = []
+
+    def __init__(self, **kwargs):
+        for param in self.parameters:
+            setattr(self, param, None)
+
+        for param, value in kwargs.items():
+            if param not in self.parameters:
+                raise HandshakeError('invalid parameter "%s"' % param)
+
+            if value is None:
+                value = True
+
+            setattr(self, param, value)
+
+    def hook_send(self, frame):
+        return frame
+
+    def hook_receive(self, frame):
+        return frame
+
+
+class Deflate(Extension):
+    rsv1 = True
+    parameters = ['max_window_bits', 'no_context_takeover']
+
+    def __init__(self, **kwargs):
+        super(Deflate, self).__init__(**kwargs)
+        self.max_window_bits = int(self.max_window_bits)
+
+    def hook_send(self, frame):
+        # FIXME: original `frame` is modified, maybe it should be copied?
+
+        if not frame.rsv1:
+            frame.rsv1 = True
+            frame.payload = self.encode(frame.payload)
+
+        return frame
+
+    def hook_recv(self, frame):
+        # FIXME: original `frame` is modified, maybe it should be copied?
+
+        if frame.rsv1:
+            frame.rsv1 = False
+            frame.payload = self.decode(frame.payload)
+
+        return frame
+
+    def encode(self, data):
+        raise NotImplementedError  # TODO
+
+    def decode(self, data):
+        raise NotImplementedError  # TODO
+
+
+def filter_compatible(extensions):
+    """
+    Remove extensions that use conflicting rsv bits and/or opcodes, with the
+    first options being most preferable.
+    """
+    rsv1_reserved = True
+    rsv2_reserved = True
+    rsv3_reserved = True
+    opcodes_reserved = []
+    compat = []
+
+    for ext in extensions:
+        if ext.rsv1 and rsv1_reserved \
+                or ext.rsv2 and rsv2_reserved \
+                or ext.rsv3 and rsv3_reserved \
+                or len(set(ext.opcodes) & set(opcodes_reserved)):
+            continue
+
+        rsv1_reserved |= ext.rsv1
+        rsv2_reserved |= ext.rsv2
+        rsv3_reserved |= ext.rsv3
+        opcodes_reserved.extend(ext.opcodes)
+        compat.append(ext)
+
+    return compat