isolateserver: add checkbox to enable ts_mon

appengine/isolate/config.py

 # Copyright 2013 The Swarming Authors. All rights reserved.
 # Use of this source code is governed by the Apache v2.0 license that can be
 # found in the LICENSE file.
 
 """Instance specific settings."""
 
 import os
 
 from google.appengine.api import app_identity
 from google.appengine.api import modules
@@ skipping 37 matching lines @@
   # id to inject into pages if applicable.
   google_analytics = ndb.StringProperty(indexed=False, default='')
 
   # Enable ts_mon based monitoring.
   enable_ts_monitoring = ndb.BooleanProperty(indexed=False, default=False)
 
   def set_defaults(self):
     self.global_secret = os.urandom(16)
     self.gs_bucket = app_identity.get_application_id()
 
+  @classmethod

[M-A Ruel, 2016/02/19 02:44:40]

This code belongs to the frontend in my opinion, not here.

[Sergey Berezin, 2016/02/19 20:35:32]

IMHO, keeping the type conversion closer to the definition of the parameters is
more intuitive. You only need to modify one class (and one file) when updating
the types, and the cast can be reused in other places, not just in the handler.

But the way it's set up now, the handler still needs to know all the parameters
anyway, so I don't feel strongly about it. Your call.

[M-A Ruel, 2016/02/19 20:37:26]

Yes but this function is purely related to form like behavior. If it were an API
for example, the format would be different. Because it is about a web form, this
is leaking the abstraction layer too low, that's why it should be in
handlers_frontend.

[Sergey Berezin, 2016/02/19 20:46:51]

OK, done.

+  def cast_to_type(cls, param_name, value):
+    """Convert parameter's value to its type.
+
+    The intended use is to convert strings from HTTP request to the
+    appropriate parameter's type.
+    """
+    def to_bool(value):
+      if type(value) is bool:
+        return value
+      return {'True': True, 'False': False}.get(value, False)
+
+    def to_str(value):
+      return str(value)
+
+    cast = {
+        'enable_ts_monitoring': to_bool,
+    }.get(param_name, to_str)
+    return cast(value)
+
 
 def settings(fresh=False):
   """Loads GlobalConfig or a default one if not present.
 
   If fresh=True, a full fetch from NDB is done.
   """
   if fresh:
     GlobalConfig.clear_cache()
   return GlobalConfig.cached()
 
 
 def get_local_dev_server_host():
   """Returns 'hostname:port' for a default module on a local dev server."""
   assert utils.is_local_dev_server()
   return modules.get_hostname(module='default')
 
 
 def warmup():
   """Precaches configuration in local memory, to be called from warmup handler.
 
   This call is optional. Everything works even if 'warmup' is never called.
   """
   settings()
   utils.get_task_queue_host()
   utils.get_app_version()