Fetch the full widget state via a control Comm

ipywidgets/__init__.py

@@ -38,6 +38,7 @@ def register_comm_target(kernel=None):
     if kernel is None:
         kernel = get_ipython().kernel
     kernel.comm_manager.register_target('jupyter.widget', Widget.handle_comm_opened)
+    kernel.comm_manager.register_target('jupyter.widget.control', Widget.handle_control_comm_opened)
 
 # deprecated alias
 handle_kernel = register_comm_target

ipywidgets/_version.py

@@ -9,6 +9,7 @@
   '' if version_info[3]=='final' else _specifier_[version_info[3]]+str(version_info[4]))
 
 __protocol_version__ = '2.0.0'
+__control_protocol_version__ = '1.0.0'
 
 # These are *protocol* versions for each package, *not* npm versions. To check, look at each package's src/version.ts file for the protocol version the package implements.
 __jupyter_widgets_base_version__ = '1.2.0'

ipywidgets/widgets/tests/test_send_state.py

@@ -3,7 +3,7 @@
 
 from traitlets import Bool, Tuple, List
 
-from .utils import setup, teardown
+from .utils import setup, teardown, DummyComm
 
 from ..widget import Widget
 
@@ -23,3 +23,12 @@ def test_empty_hold_sync():
     with w.hold_sync():
         pass
     assert w.comm.messages == []
+
+
+def test_control():
+    comm = DummyComm()
+    Widget.close_all()
+    w = SimpleWidget()
+    Widget.handle_control_comm_opened(comm, {})
+    Widget.handle_control_comm_msg({'type': 'models-request'})
+    assert comm.messages

ipywidgets/widgets/widget.py

@@ -25,8 +25,9 @@
 
 from base64 import standard_b64encode
 
-from .._version import __protocol_version__, __jupyter_widgets_base_version__
+from .._version import __protocol_version__, __control_protocol_version__, __jupyter_widgets_base_version__
 PROTOCOL_VERSION_MAJOR = __protocol_version__.split('.')[0]
+CONTROL_PROTOCOL_VERSION_MAJOR = __control_protocol_version__.split('.')[0]
 
 def _widget_to_json(x, obj):
     if isinstance(x, dict):
@@ -290,6 +291,7 @@ class Widget(LoggingHasTraits):
     # Class attributes
     #-------------------------------------------------------------------------
     _widget_construction_callback = None
+    _control_comm = None
 
     # widgets is a dictionary of all active widget objects
     widgets = {}
@@ -302,7 +304,6 @@ def close_all(cls):
         for widget in list(cls.widgets.values()):
             widget.close()
 
-
     @staticmethod
     def on_widget_constructed(callback):
         """Registers a callback to be called when a widget is constructed.
@@ -317,6 +318,51 @@ def _call_widget_constructed(widget):
         if Widget._widget_construction_callback is not None and callable(Widget._widget_construction_callback):
             Widget._widget_construction_callback(widget)
 
+    @classmethod
+    def handle_control_comm_opened(cls, comm, msg):
+        """
+        Class method, called when the comm-open message on the
+        "jupyter.widget.control" comm channel is received
+        """
+        version = msg.get('metadata', {}).get('version', '')
+        if version.split('.')[0] != CONTROL_PROTOCOL_VERSION_MAJOR:
+            raise ValueError("Incompatible widget control protocol versions: received version %r, expected version %r"%(version, __control_protocol_version__))
+
+        cls._control_comm = comm
+        cls._control_comm.on_msg(cls._handle_control_comm_msg)
+
+    @classmethod
+    def _handle_control_comm_msg(cls, msg):
+        # This shouldn't happen unless someone calls this method manually
+        if cls._control_comm is None:
+            raise RuntimeError('Control comm has not been properly opened')
+
+        data = msg['content']['data']
+        method = data['method']
+
+        if method == 'request_states':
+            # Send back the full widgets state
+            cls.get_manager_state()
+            widgets = cls.widgets.values()
+            full_state = {}
+            drop_defaults = False
+            for widget in widgets:
+                full_state[widget.model_id] = {
+                    'model_name': widget._model_name,
+                    'model_module': widget._model_module,
+                    'model_module_version': widget._model_module_version,
+                    'state': widget.get_state(drop_defaults=drop_defaults),
+                }
+            full_state, buffer_paths, buffers = _remove_buffers(full_state)
+            cls._control_comm.send(dict(
+                method='update_states',
+                states=full_state,
+                buffer_paths=buffer_paths
+            ), buffers=buffers)
+
+        else:
+            self.log.error('Unknown front-end to back-end widget control msg with method "%s"' % method)
+
     @staticmethod
     def handle_comm_opened(comm, msg):
         """Static method, called when a widget is constructed."""

packages/base/src/version.ts

@@ -6,4 +6,3 @@ const JUPYTER_WIDGETS_VERSION = '1.2.0';
 
 export
 const PROTOCOL_VERSION = '2.0.0';
-

packages/schema/messages.md

@@ -338,3 +338,44 @@ To display a widget, the kernel sends a Jupyter [iopub `display_data` message](h
   }
 }
 ```
+
+
+
+
+# Control Widget messaging protocol, version 1.0
+
+This is implemented in ipywidgets 7.7.
+
+### The `jupyter.widget.control` comm target
+
+A kernel-side Jupyter widgets library registers a `jupyter.widget.control` comm target that is used for fetching all widgets states through a "one shot" comm message (one for all widget instances). Unlike the `jupyter.widget` comm target, the created comm is global to all widgets,
+
+#### State requests: `request_states`
+
+When a frontend wants to request the full state of a all widgets, the frontend sends a `request_states` message:
+
+```
+{
+  'comm_id' : 'u-u-i-d',
+  'data' : {
+    'method': 'request_states'
+  }
+}
+```
+
+The kernel side of the widget should immediately send an `update_states` message with all widgets states:
+
+```
+{
+  'comm_id' : 'u-u-i-d',
+  'data' : {
+    'method': 'update_states',
+    'states': {
+      <widget1 u-u-i-d>: <widget1 state>,
+      <widget2 u-u-i-d>: <widget2 state>,
+      [...]
+    },
+    'buffer_paths': [ <list with paths corresponding to the binary buffers> ]
+  }
+}
+```