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SockMux server
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SockMux is an experimental protocol designed for inter-DeleGate communication.
It is a simple protocol for "port forwarding" to accept, relay and destroy
connections, multiplexed over a single persistent connection.
A pair of SockMux-DeleGate establish and retain a connection between them,
then forward port from local to remote each other over the connection.
The persistent connection is established with "-Phost:port" parameter at receptor side, and "SERVER=sockmux://host:port" at connector side. The port to accept outgoing connections to be forwarded to remote is specified with PORT="listOfPorts parameter. The server to be connected for incoming connections from remote is specified with a postfix string ",-in" like SERVER="telnet://host:23,-in".
An incoming connection can be processed with DeleGate as a proxy of the specified protocol. If only protocol name is specified like SERVER="telnet,-in", or if "-in" is postfixed like "-in(option list)", then a DeleGate is invoked to process the connection. The option list is passed to the invoked DeleGate as the list of command line options. For example, SERVER="telnet://host,-in(+=config.cnf)" will invoke a DeleGate with command line options like ``delegated SERVER=telnet://host +=config.cnf''.
Example: bi-directional SockMux-DeleGate
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hostX% delegated SERVER=sockmux -PhostX:9000 PORT=9023 SERVER="telnet://hostX,-in"
hostY% delegated SERVER=sockmux://hostX:9000 PORT=9023 SERVER="telnet://hostY,-in"
// a pair of SockMux-DeleGate is connected at the port "hostX:9000", then
// the port "hostX:9023" is forwarded to "telnet://hostY"
// the port "hostY:9023" is forwarded to "telnet://hostX"
Example: uni-directional SockMux-DeleGate
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hostX% delegated SERVER=sockmux -PhostX:9000 SERVER="telnet://hostX,-in"
hostY% delegated SERVER=sockmux://hostX:9000 PORT=hostY:9023
// hostY:9023 is forwarded to "telnet://hostX".
Example: uni-directional to proxy-Telent-DeleGate
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hostX% delegated SERVER=sockmux -PhostX:9000 PORT=hostX:9023
hostY% delegated SERVER=sockmux://hostX:9000 SERVER="telnet,-in"
// hostX:9023 is forwarded to a Telnet proxy on hostY.
When SockMux is used just to relay data between sockets, without interpreting the application protocol relayed over SockMux, such relaying can be represented with simpler expression using DEST parameter instead of SERVER as follows:
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DEST=host:port[:srcHostList]
for
SERVER=tcprelay://host:port,-in[:-:srcHostList]
DEST=host:port/udp[:srcHostList] for SERVER=udprelay://host:port,-in[:-:srcHostList]
Example: tcprelay over SockMux
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hostX% delegated SERVER=sockmux://hostY:9000 PORT=hostX:111
hostY% delegated SERVER=sockmux -PhostY:9000 DEST=hostT:111
// hostX:111/tcp is forwarded to the server at hostT:111/tcp via hostY.
Example: relaying UDP over SockMux/TCP
Another way to establish a persistent connection between two SockMux-DeleGate is using a FIFO device like named pipe. It is specified like SERVER=sockmux:commtype@fifoName where commtype is one of "commin", "commout", and "comm", which represents uni-directional input, uni-directional output and bi-directional input/output respectively.
Example: use fifo device on a host
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% mkfifo /tmp/com0
% mkfifo /tmp/com1
serv1) SERVER=sockmux:commin@/tmp/com0 SERVER=sockmux:commout@/tmp/com1 ...
serv2) SERVER=sockmux:commin@/tmp/com1 SERVER=sockmux:commout@/tmp/com0 ...
Example: use communication port between two hosts (not tested yet)
The persistent connection can be established by a given external program invoked by DeleGate. The process of the program is passed a socket to/from DeleGate at file descriptor number 0 and 1;
Example: establish connection by external command
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% SERVER="sockmux:proc@connectCommand" ...
The destination SERVER for an incoming connection from remote can be selected depending on which port it was accepted. A SERVER parameter postfixed with ":-:-Pxxxx" will be applied only to connections which is accepted on remote host with PORT=xxxx.
Example: forwarding multiple port
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hostX% ... PORT=8023,8080
hostY% ... SERVER=telnet,-in:-:-P8023 SERVER=http,-in:-:-P8080
// hostX:8023 is forwarded to Telnet-proxy on hostY
// hostX:8080 is forwarded to HTTP-proxy on hostY
NOTE: forwarding FTP data connection is not supported (yet).