Custom markdown filter, 3rd party one wasn't thread safe

setup.py

@@ -23,7 +23,7 @@ INSTALL_REQUIRES = [
 	"Flask-Principal>=0.3.5,<0.4",
 	"Flask-Babel>=0.9,<0.10",
 	"Flask-Assets>=0.10,<0.11",
-	"Flask-Markdown>=0.3,<0.4",
+	"markdown>=2.6.4,<2.7",
 	"pyserial>=2.7,<2.8",
 	"netaddr>=0.7.17,<0.8",
 	"watchdog>=0.8.3,<0.9",

src/octoprint/server/__init__.py

@@ -12,7 +12,6 @@ from flask.ext.login import LoginManager, current_user
 from flask.ext.principal import Principal, Permission, RoleNeed, identity_loaded, UserNeed
 from flask.ext.babel import Babel, gettext, ngettext
 from flask.ext.assets import Environment, Bundle
-from flaskext.markdown import Markdown
 from babel import Locale
 from watchdog.observers import Observer
 from watchdog.observers.polling import PollingObserver
@@ -649,7 +648,8 @@ class Server(object):
 			response.headers.add("X-Clacks-Overhead", "GNU Terry Pratchett")
 			return response
 
-		Markdown(app)
+		from octoprint.util.jinja import MarkdownFilter
+		MarkdownFilter(app)
 
 	def _setup_i18n(self, app):
 		global babel

src/octoprint/util/jinja.py

@@ -159,3 +159,18 @@ class ExceptionHandlerExtension(Extension):
 			return "Unknown error"
 
 trycatch = ExceptionHandlerExtension
+
+
+class MarkdownFilter(object):
+
+	def __init__(self, app, **markdown_options):
+		self._markdown_options = markdown_options
+		app.jinja_env.filters.setdefault("markdown", self)
+
+	def __call__(self, stream):
+		from jinja2 import Markup
+		from markdown import Markdown
+
+		# Markdown is not thread safe
+		markdown = Markdown(**self._markdown_options)
+		return Markup(markdown.convert(stream))