aprilsh

README

Aprilsh: remote shell support intermittent or mobile network. Inspired by [mosh](https://mosh.org/) and [zutty](https://github.com/tomscii/zutty). aprilsh is a remote shell based on UDP, authenticate user via openssh.

Installation

Requirement

• open-ssh is a must requirement, sshd is required to perform user authentication.
• ncurses and terminfo is a must requirement.
• systmd is required by redhat linux family (fedora, centos, redhat).
• openrc is required by alpine linux.
• utmps is required by alpine linux.
• logrotate is a optional requirement by alpine.
• locale support is a build requirement.

If you prefer to build aprilsh manually, please refer to this document

Alpine linux

Before start apshd, you need to make sure you can ssh login to the target server, please refer to this doc to setup a ssh enabled docker container. Refer to build doc to know how to build apk packages and private repositories.

# add testing repositories
echo "https://dl-cdn.alpinelinux.org/alpine/edge/testing" >> /etc/apk/repositories
# update repositories metadata
apk update
# install client and server
apk add aprilsh

Now you can ssh login to the server, it's time to start apshd server and login with apsh.

# start apshd server
rc-service apshd start
# apsh login with port mapping
apsh -m 100 eric@localhost:8022
# apsh login without port mapping
apsh eric@localhost

After apsh login, you connection to the remote server is provided by aprilsh.

Fedora, CentOS, Redhat linux

Before start apshd, you need to make sure you can ssh login to the target server, please refer to this doc to setup a ssh enabled docker container.

Note: This is a private yum/dnf repositories, it only provides x86_64 packages. Refer to rpms doc to understand how to build rpm packages and dnf repositories.

# import public key to rpm DB
rpm --import https://ericwq.codeberg.page/RPM-GPG-KEY-wangqi
# add new repo to dnf repository
dnf config-manager --add-repo https://ericwq.codeberg.page/aprilsh.repo
# install client and server
dnf install -y aprilsh

Now you can ssh login to the server, it's time to start apshd service and login with apsh.

sudo systemctl start apshd.service      # start apshd service
sudo journalctl -f -u apshd.service     # keep reading the latest apshd.service log
apsh -m 100 packager@localhost:8022     # apsh login to server
apsh packager@localhost                 # apsh login without port mapping

After apsh login, you connection to the remote server is provided by aprilsh.

MacOS

Run the following command to install aprilsh client for macOS.

brew tap ericwq/utils                   # add tap to homebrew
brew install aprilsh                    # only install aprilsh client

After apsh login, you connection to the remote server is provided by aprilsh.

Refer to homebrew doc to know how to create homebrew package and tap.

Validate installation

by default apshd listen on udp localhost:8100.

openrc-nvide:~# netstat -lup
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
udp        0      0 localhost:8100          0.0.0.0:*                           45561/apshd
openrc-nvide:~#

now login to the system with apsh (aprilsh client), note the motd(welcome message) depends on your linux system.

qiwang@Qi15Pro client % apsh ide@localhost
openrc-nvide:0.10.2

Lua, C/C++ and Golang Integrated Development Environment.
Powered by neovim, luals, gopls and clangd.
ide@openrc-nvide:~ $

if you login on two terminals, on the server, there will be two server processes serve the clients. the following shows apshd serve two clients. one is:8101, the other is ':8102'

openrc:~# netstat -lp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:ssh             0.0.0.0:*               LISTEN      225/sshd [listener]
tcp        0      0 :::ssh                  :::*                    LISTEN      225/sshd [listener]
udp        0      0 localhost:8100          0.0.0.0:*                           45561/apshd
udp        0      0 :::8101                 :::*                                45647/apshd
udp        0      0 :::8102                 :::*                                45612/apshd
Active UNIX domain sockets (only servers)
Proto RefCnt Flags       Type       State         I-Node PID/Program name    Path
unix  2      [ ACC ]     STREAM     LISTENING     872486 159/s6-ipcserverd   /run/utmps/.btmpd-socket
unix  2      [ ACC ]     STREAM     LISTENING     869747 253/s6-ipcserverd   /run/utmps/.utmpd-socket
unix  2      [ ACC ]     STREAM     LISTENING     866239 281/s6-ipcserverd   /run/utmps/.wtmpd-socket
openrc-nvide:~#

Motivation

openSSH is excellent. While mosh provides better keystroke prediction/latency and is capable of handle WiFi/cellular mobile network roaming. But mosh project is not active anymore and no release sine 2017. Such a good project like mosh should keeps developing.

After read through mosh source code, I decide to rewrite it with golang. Go is my first choice because the C++ syntax is too complex. Go also has excellent support for UTF-8 and multithreaded programming. The last reason: go compiler is faster than c++ compiler.

There are several rules for this project:

• Keep base design of mosh: SSP, UDP, keystroke prediction.
• Use 3rd party library as less as possible to keep it clean.

There are also some goals for this project:

• Full UTF-8 support, including emoji and flag support.
• Support terminal 24bit color.
• Upgrade to proto3
• Use terminfo database for better compatibility.
• Prove golang is a good choice for terminal developing.

The project name Aprilsh is derived from April+sh. This project started in shanghai April 2022, and it's a remote shell. Use the above command to add musl locales support and utmps support for alpine. Note alpine only support UTF-8 charmap.

Improvement

• prediction engine evaluate based on both user input response and server side timeout
• prediction engine support chinese character
• support XTGETTCAP, SGR 1006, synchronized output, OSC 8, CSI u
• support htop arrow key (mosh has a bug)
• support large volumes of output generated from terminal application (mosh has a bug)
• plan to support terminal query across multi-terminal emulator

Architecture

• The green part is provided by the system/terminal emulator. Such as alacritty or kitty.
• The cyan part is provided by Aprilsh.
• The yellow part is our target terminal application. In the above diagram it's neovim.
• Actually the yellow part can be any terminal based application: emcas, neovim, htop, etc.
• The rest part is provided by the system.

Set GOFLAGS="-tags=utmps" APRILSH_APSHD_PATH=~/.local/bin/apshd before nvim.

Changelog

Ready for early access. Check here for history detail.

License

MIT