From 3113e2809249e1fa9a1c71f3e210d4d74ae47502 Mon Sep 17 00:00:00 2001
From: Aaron LI <aaronly.me@outlook.com>
Date: Wed, 9 Nov 2016 20:21:22 +0800
Subject: webui: Add "WebSocketLogHandler" to push log to client through
 WebSocket

---
 fg21sim/webui/loghandler.py | 61 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 fg21sim/webui/loghandler.py

diff --git a/fg21sim/webui/loghandler.py b/fg21sim/webui/loghandler.py
new file mode 100644
index 0000000..0b457b5
--- /dev/null
+++ b/fg21sim/webui/loghandler.py
@@ -0,0 +1,61 @@
+# Copyright (c) 2016 Weitian LI <liweitianux@live.com>
+# MIT license
+
+"""
+Custom logging handlers
+
+WebSocketLogHandler :
+    Send logging messages to the WebSocket as JSON-encoded string.
+"""
+
+
+import logging
+import json
+
+
+class WebSocketLogHandler(logging.Handler):
+    """
+    Send logging messages to the WebSocket as JSON-encoded string.
+
+    Parameters
+    ----------
+    websocket : `~tornado.websocket.WebSocketHandler`
+        An `~tornado.websocket.WebSocketHandler` instance, which has
+        the ``write_message()`` method that will be used to send the
+        logging messages.
+    msg_type : str, optional
+        Set the type of the sent back message, for easier processing
+        by the client.
+
+    NOTE
+    ----
+    The message sent through the WebSocket is a JSON-encoded string
+    from a dictionary, e.g.,
+    ``{"type": self.msg_type,
+       "action": "log",
+       "levelname": record.levelname,
+       "levelno": record.levelno,
+       "name": record.name,
+       "asctime": record.asctime,
+       "message": <formatted-message>}``
+    """
+    def __init__(self, websocket, msg_type=None):
+        super().__init__()
+        self.websocket = websocket
+        self.msg_type = msg_type
+
+    def emit(self, record):
+        try:
+            message = self.format(record)
+            msg = json.dumps({
+                "type": self.msg_type,
+                "action": "log",
+                "levelname": record.levelname,
+                "levelno": record.levelno,
+                "name": record.name,
+                "asctime": record.asctime,
+                "message": message,
+            })
+            self.websocket.write_message(msg)
+        except Exception:
+            self.handleError(record)
-- 
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