In this case, a filter channel is used. The implementation of RPCs changed significantly in DP 4.0. The new mechanism allows RPCs to be issued over any Tcl channel, and handles duplicate or out of order return of RPCs. These changes make the new protocol incompatible with previous versions, but we felt the new features and bug fixes justified the incompatibility. Length is a six digit decimal string that gives the size of the entire packet, including the length field itself.
Space is a delimiter between fields and is simply the space character.
Type is a one byte token character that denotes the type of this packet. Finally, msg is the Tcl command to be evaluated. This callback reads the message, buffering partial reads if necessary. If the packet is an RDO, the command is evaluated. Nothing is returned to the sender.