log exceptions in Comm handlers

IPython/html/static/services/kernels/js/comm.js

@@ -74,7 +74,13 b' var IPython = (function (IPython) {'
         }
         var comm = new Comm(content.comm_id);
         this.register_comm(comm);
+        try {
         f(comm, msg);
+        } catch (e) {
+            console.log("Exception opening new comm:", e, msg);
+            comm.close();
+            this.unregister_comm(comm);
+        }
     };
     
     CommManager.prototype.comm_close = function (msg) {
@@ -84,7 +90,11 b' var IPython = (function (IPython) {'
             return;
         }
         delete this.comms[content.comm_id];
+        try {
         comm.handle_close(msg);
+        } catch (e) {
+            console.log("Exception closing comm: ", e, msg);
+        }
     };
     
     CommManager.prototype.comm_msg = function (msg) {
@@ -93,7 +103,11 b' var IPython = (function (IPython) {'
         if (comm === undefined) {
             return;
         }
+        try {
         comm.handle_msg(msg);
+        } catch (e) {
+            console.log("Exception handling comm msg: ", e, msg);
+        }
     };
     
     //-----------------------------------------------------------------------

IPython/kernel/comm/manager.py

@@ -79,8 +79,10 b' class CommManager(LoggingConfigurable):'
     def register_target(self, target_name, f):
         """Register a callable f for a given target name
         
-        f will be called with a Comm object as its only argument
-        when a comm_open message is received with `target`.
+        f will be called with two arguments when a comm_open message is received with `target`:
+        
+        - the Comm instance
+        - the `comm_open` message itself.
         
         f can be a Python callable or an import string for one.
         """
@@ -141,7 +143,12 b' class CommManager(LoggingConfigurable):'
             comm.close()
             return
         self.register_comm(comm)
+        try:
         f(comm, msg)
+        except Exception:
+            self.log.error("Exception opening comm with target: %s", target_name, exc_info=True)
+            comm.close()
+            self.unregister_comm(comm_id)
     
     @with_output
     def comm_msg(self, stream, ident, msg):
@@ -152,7 +159,10 b' class CommManager(LoggingConfigurable):'
         if comm is None:
             # no such comm
             return
+        try:
         comm.handle_msg(msg)
+        except Exception:
+            self.log.error("Exception in comm_msg for %s", comm_id, exc_info=True)
     
     @with_output
     def comm_close(self, stream, ident, msg):
@@ -162,9 +172,14 b' class CommManager(LoggingConfigurable):'
         comm = self.get_comm(comm_id)
         if comm is None:
             # no such comm
+            self.log.debug("No such comm to close: %s", comm_id)
             return
         del self.comms[comm_id]
+        
+        try:
         comm.handle_close(msg)
+        except Exception:
+            self.log.error("Exception handling comm_close for %s", comm_id, exc_info=True)
 
 
 __all__ = ['CommManager']