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10.3.2 Accepting and Refusing Connections

 

By default, NExS is set to ``refuse'' connections, meaning that an external program cannot compel an NExS spreadsheet to accept connections. From the NExS side, connections are controlled using the following Connections menu selections:

Accept Connections -
tells NExS that it should accept requests for connection. Remote clients seeking connections will connect with the NExS spreadsheet that most recently executed the Accept Connections operation.
Refuse Connections -
tells NExS to refuse connection attempts from client programs. This operation has no effect on existing connections.
Lock Connections -
  tells NExS to lock out the NExS Connection manager from connecting to an NExS instance.
Connection List... -
  displays current connections by port number and name. You can display this dialog box during other NExS operations, if you wish to stay informed of current connection status.

To set NExS to accept connections, select Accept Connections from the Connections menu.

Note that at any given time, only one instance of NExS on your X Window display can be set to accept connections. If you are running more than one instance NExS on your display and set one instance to accept connections, all other instances will automatically be set to Refuse Connections (unless they were already set to Lock Connections - see below). The reason for this behavior is to avoid ambiguity when a client application attempts to connect to a NExS instance running on your display.

    For security reasons, you may want to prevent external applications from connecting to your NExS spreadsheets. Selecting Refuse Connections is sufficient to prevent ``normal'' client applications from connecting. However, NExS supports a special class of client application called a ``connection manager'' which has special abilities to interact with all of the NExS instances running on your display. A connection manager application can connect to NExS instances even if they are set to Refuse Connections. To disallow all external applications, including connection managers, from connecting to NExS you must set Lock Connections from the Connections menu.

Note that setting NExS to Refuse or Lock Connections after one or more client applications have connected to the spreadsheet does not disable those existing connections. It does prevent new connections from being established, however. Once a connection is established, it remains connected until it is explicitly disconnected, or until the NExS instance to which it is connected terminates.

The current ``connectability'' status (accept/refuse/lock) can be determined by observing which of the three options is not grayed out on the Connections menu.


The standard X Window authorization mechanisms, xhost (which is relatively insecure) and xauth (which is relatively secure), provide an added layer of security between NExS and client applications running over a network.

To display a list of current client connections:

  1. Select Connections List from the Connections menu. NExS displays Active Connections dialog box as shown in Figure 10.4. This dialog box lists the client programs that are presently connected to the spreadsheet. The information contained in this dialog box is updated immediately after any change in connection status.

  2. Click Cancel to dismiss the dialog box.

   figure3478
Figure 10.4: Active Connections Dialog Box


next up previous contents index
Next: 11 Printing the Spreadsheet Up: 10.3 Connecting NExS to Previous: 10.3.1 How Connections Work

NExS User's Guide, Version 1.4.5
Grey Trout Software
11 April 1999