Notes on using the Samsung Galaxy s7 (and similar) Keyboard Cover with termux and ssh

I have been a diehard hardware keyboard user on Android phones starting from the HTC Dream, Desire and finally the Galaxy S Relay which seemed to be the end of the line...

Recently I found out that Samsung is making a Keyboard Cover add-on for the newer Galaxy S series phones including the S7 and the S8 and picked one of these up to replace my ancient Relay.

My main use case for the keyboard is ssh. On the S7 I use https://termux.com/ and this setup is workable out of the box with some annoyances and limitations:

Ctrl and ESC

The keyboard cover has no way to generate Ctrl shifted characters or ESC. Termux allows working around this by using the volume up/down buttons or on-screen buttons which is workable but not perfect.

Termux also allows configuring the Back key to send ESC by putting the following lines in .termux/termux.properties:

bell-character=ignore
back-key=escape

This takes care of ESC. For Ctrl I decided to use the keyboard's "$" as a Ctrl prefix. This could be done by modifying Termux and maybe I will try that later but for now I decided to handle it on the Linux side. At first I attempted to do it with the tmux configuration in ctrlhack.tmux

This mostly works but it doesn't allow sending the tmux escape sequence itself using the $ key. So I wrote a small pty wrapper to do the translation that which be found in ctrlhack.go

Since it's written in Go and uses only pure Go libraries it is trivial to cross-compile to an Arm binary that will run on Android:

go get -d .
GOARCH=arm go build -o ctrlhack-arm

It will launch bash or the executable specified in the first argument. In the child shell (or process) you can type "$c" for Ctrl-C and enter other Ctrl shifted characters similarly. "$$" will emit a real "$".

Other notes

• The keyboard cover only works with the "Samsung Keyboard" virtual keyboard. This means that it cannot be used with "Hacker's Keyboard" and may not work with custom ROMs.
• Samsung Themes doesn't work with the Keyboard Cover
• No search key, I miss that in the browser and some other apps that supported it and also for quick launch
• There is not backlight so not great in complete dark but the shape of the keys is easy to make out with your fingertips

Despite these shortcomings this is probably still the best pocket-ssh solution on a modern device.