[WIP] Dash Dev Tools -- backend

dash/dash.py

@@ -8,14 +8,16 @@
 import pkgutil
 import warnings
 import re
+import traceback
 
 from functools import wraps
 
 import plotly
 import dash_renderer
 import flask
-from flask import Flask, Response
+from flask import Flask, Response, got_request_exception
 from flask_compress import Compress
+from flask_socketio import SocketIO
 
 from .dependencies import Event, Input, Output, State
 from .resources import Scripts, Css
@@ -114,6 +116,7 @@ def __init__(
         self.index_string = index_string
         self._meta_tags = meta_tags or []
         self._favicon = None
+        self._errors = ""
 
         if compress:
             # gzip
@@ -760,4 +763,25 @@ def run_server(self,
                    port=8050,
                    debug=False,
                    **flask_run_options):
-        self.server.run(port=port, debug=debug, **flask_run_options)
+        if debug:
+            socketio = SocketIO(self.server)
+
+            @got_request_exception.connect_via(self.server)
+            # pylint: disable=unused-variable
+            def when_dash_gets_exception(server, exception, **extra):
+                socketio.emit(
+                    'error',
+                    {
+                        'errorType': type(exception).__name__,
+                        'errorMessage': str(exception),
+                        'errorTraceback': traceback.format_exc(),
+                    },
+                    namespace=(
+                        '{}_dash-errors'
+                        .format(self.config['routes_pathname_prefix'])
+                    )
+                )
+
+            socketio.run(self.server, port=port, debug=debug)
+        else:
+            self.server.run(port=port, debug=debug, **flask_run_options)

dev-requirements.txt

@@ -13,3 +13,4 @@ plotly>=2.0.8
 requests[security]
 flake8
 pylint==1.9.2
+Flask-SocketIO==3.0.1

requirements.txt

@@ -10,6 +10,7 @@ enum34==1.1.6
 Flask==0.12
 Flask-Compress==1.4.0
 Flask-SeaSurf==0.2.2
+Flask-SocketIO==3.0.1
 funcsigs==1.0.2
 functools32==3.2.3.post2
 ipdb==0.10.2