tcp-multiplexer

README

tcp-multiplexer

Use it in front of a target server and let your client programs connect to it, if target server only allows you to create a limited number of TCP connections concurrently. While it has its limitation: increased latency as incoming request will block each other.

A common use case for tcp-multiplexer is to allow multiple modbus/TCP clients connect to solar inverters which often only support a single TCP connection.

Architecture

┌──────────┐
│ ┌────────┴──┐      ┌─────────────────┐      ┌───────────────┐
│ │           ├─────►│                 │      │               │
│ │ client(s) │      │ tcp-multiplexer ├─────►│ target server │
└─┤           ├─────►│                 │      │               │
  └───────────┘      └─────────────────┘      └───────────────┘


─────► TCP connection

drawn by https://asciiflow.com/

Unlike with a reverse proxy, the TCP connection between tcp-multiplexer and the target server will be reused for all clients' TCP connections.

Multiplexer is simple. For every TCP connection from clients, the handling logic:

for {
get lock...
data pipe:
	1. get request message from client
	2. forward request message to target server
	3. get response message from target server
	4. forward response message to client
release lock...
}

The lock makes sure that at any time, the TCP connection to the target server will be used in exactly one request-response loop. This way, all connections from clients share one TCP connection to the target server.

Next key point is how to detect message (e.g., HTTP) from the TCP data stream.

Supported application protocols

Every application protocol (request–response message exchange pattern) has its own message format. The following formats are supported currently:

1. echo: \n terminated
2. http1 (not including https, websocket): not fully supported
3. iso8583: with 2 bytes header of the length of iso8583 message
4. modbus-tcp

$ ./tcp-multiplexer list                                    
* iso8583
* echo
* http
* modbus

usage for example: ./tcp-multiplexer server -p echo

See detailed: https://github.com/ingmarstein/tcp-multiplexer/tree/master/example

Usage

$ ./tcp-multiplexer server -h
start multiplexer proxy server

Usage:
  tcp-multiplexer server [flags]

Flags:
  -p, --applicationProtocol string   multiplexer will parse to message echo/http/iso8583 (default "echo")
      --delay duration               delay after connect
  -h, --help                         help for server
  -l, --listen string                multiplexer will listen on (default "8000")
  -t, --targetServer string          multiplexer will forward message to (default "127.0.0.1:1234")
      --timeout int                  timeout in seconds (default 60)

Global Flags:
  -v, --verbose   verbose log

In a container

docker run ghcr.io/ingmarstein/tcp-multiplexer server -t 127.0.0.1:1234 -l 8000 -p modbus

Alternatively, use the included compose.yml file as a template if you prefer to use Docker Compose.

Testing

Start echo server (listen on port 1234)

$ go run example/echo-server/main.go
1: 127.0.0.1:1234 <-> 127.0.0.1:58088

Start TCP multiplexing (listen on port 8000)

$ ./tcp-multiplexer server -p echo -t 127.0.0.1:1234 -l 8000
INFO[2021-05-09T02:06:40+08:00] creating target connection
INFO[2021-05-09T02:06:40+08:00] new target connection: 127.0.0.1:58088 <-> 127.0.0.1:1234
INFO[2021-05-09T02:07:57+08:00] #1: 127.0.0.1:58342 <-> 127.0.0.1:8000
INFO[2021-05-09T02:08:16+08:00] closed: 127.0.0.1:58342 <-> 127.0.0.1:8000
INFO[2021-05-09T02:08:19+08:00] #2: 127.0.0.1:58402 <-> 127.0.0.1:8000

client test

$ nc 127.0.0.1 8000
kkk
kkk
^C
$ nc 127.0.0.1 8000
mmm
mmm

Documentation

Overview

Copyright © 2021 xujiahua <littleguner@gmail.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.