User friendly way to close websocket with code (via CloseException) (#468)

* User friendly way to close websocket with status

* More generic way  to close(whatever) connection by exception

* Fix import ordering for exceptions (isort)

channels/exceptions.py

@@ -1,3 +1,7 @@
+from __future__ import unicode_literals
+import six
+
+
 class ConsumeLater(Exception):
     """
     Exception that says that the current message should be re-queued back
@@ -39,6 +43,33 @@ class DenyConnection(Exception):
     pass
 
 
+class ChannelSocketException(Exception):
+    """
+    Base Exception is intended to run some action ('run' method)
+    when it is raised at a consumer body
+    """
+
+    def run(self, message):
+        raise NotImplementedError
+
+
+class WebsocketCloseException(ChannelSocketException):
+    """
+    ChannelSocketException based exceptions for close websocket connection with code
+    """
+
+    def __init__(self, code=None):
+        if code is not None and not isinstance(code, six.integer_types) \
+                and code != 1000 and not (3000 <= code <= 4999):
+            raise ValueError("invalid close code {} (must be 1000 or from [3000, 4999])".format(code))
+        self._code = code
+
+    def run(self, message):
+        if message.reply_channel.name.split('.')[0] != "websocket":
+            raise ValueError("You cannot raise CloseWebsocketError from a non-websocket handler.")
+        message.reply_channel.send({"close": self._code or True})
+
+
 class SendNotAvailableOnDemultiplexer(Exception):
     """
     Raised when trying to send with a WebsocketDemultiplexer. Use the multiplexer instead.

channels/worker.py

@@ -8,7 +8,7 @@ import sys
 import threading
 import time
 
-from .exceptions import ConsumeLater, DenyConnection
+from .exceptions import ChannelSocketException, ConsumeLater, DenyConnection
 from .message import Message
 from .signals import consumer_finished, consumer_started, worker_ready
 from .utils import name_that_thing
@@ -122,6 +122,8 @@ class Worker(object):
                 if message.channel.name != "websocket.connect":
                     raise ValueError("You cannot DenyConnection from a non-websocket.connect handler.")
                 message.reply_channel.send({"close": True})
+            except ChannelSocketException as e:
+                e.run(message)
             except ConsumeLater:
                 # They want to not handle it yet. Re-inject it with a number-of-tries marker.
                 content['__retries__'] = content.get("__retries__", 0) + 1