To use the interface, the Tcl program needs to be attached to the ECLiPSe program. The attach request is initiated on the ECLiPSe side, by calling the predicate remote_connect/3 2 from ECLiPSe. The Tcl program is then attached to the ECLiPSe program by executing the procedure ec_remote_init from Tcl. If no error occurs, then the connection is established and the interface is set up.
In more detail, the ECLiPSe predicate remote_connect/3 establishes a socket listening for the connection from the Tcl side. It prints out, on the stream log_output, the hostname and the port number that the Tcl side should connect to:
[eclipse 1]: remote_connect(Host/Port, Control, _InitGoal). Socket created at address chicken.icparc.ic.ac.uk/25909
On the Tcl side, ec_remote_init is called with the hostname and port number given by remote_connect/3:
ec_remote_init chicken.icparc.ic.ac.uk 25909
If successful, some initial links are established between the two sides, such as the control connection and the connection to allow rpc goals to be sent from the Tcl to the ECLiPSe side. After the attachment, optional user-defined initialisations are performed on both sides (via the InitGoal argument on the ECLiPSe side, and the init_command on the Tcl side), and the two sides can then interact. Initially, the control is given to the Tcl side, and remote_connect/3 returns only when control is handed over to the ECLiPSe side.
As part of the attachment process, the ECLiPSe name of the control connection is passed to the Tcl side. This can be accessed by the user using the command:
Unimplemented functionality error will be raised if the Tcl or ECLiPSe side are incompatible with each other. This can happen if one side is outdated, e.g. if the remote Tcl interface used and the ECLiPSe being connected to are not from the same version of ECLiPSe. In this case, it is best to update both sides to the latest version of ECLiPSe.
Once a Tcl side is attached to an ECLiPSe, the Tcl side can execute
ECLiPSe goals on the ECLiPSe side via the ec_rpc mechanism. This
may be a security concern as
this gives the Tcl side as much access to the resources on the ECLiPSe
side as the ECLiPSe process itself, even though the Tcl side can
potentially be anywhere reachable from the ECLiPSe side via TCP.
However, the connection must be initiated from the ECLiPSe side, and the
attachment process must follow a protocol in order for a successful
if a third party somehow knew which Address to connect to, and follows the
protocol, it can ‘steal’ the connection to ECLiPSe. No
authentication is performed by the simple
but remote_connect_accept/6 does allow a simple authentication
where it can require the Tcl side to send an ECLiPSe term that matches
the one specified in calling the predicate. This is done before the Tcl
side is given the ability to run rpc goals on the ECLiPSe side.
It is also possible to limit the remote connection to the same machine as the
ECLiPSe process by specifying ‘localhost’ as the host name in the
Host/Port address of
remote_connect/3. The Tcl side must also
use ‘localhost’ for the Host name in its client connection.
Each peer queue is created by creating a new server socket on the ECLiPSe side and then accepting a client connection from the Tcl side. The accept command is told where the client connection is from, and the client host is checked against the client’s host from the attachment, to ensure that the same host has been connected. If not, the ECLiPSe side will reject the particular connection. At this point, the security has probably been compromised, and the two side should disconnect.
Note also that by default, none of the information sent through the queues between the remote side and the ECLiPSe side is encrypted. If the programmer requires these communication channels to be secure, then such encryptions need to be provided by the programmer.