maanantai 26. kesäkuuta 2017

Writing your own simple GUI SSH client

Most Unix users are accustomed to using SSH from the command line. On Windows and other platforms GUI tools are popular and they can do some nice tricks such as opening graphical file transfer windows and initiate port forwardings to an existing connection. You can do all the same things with the command line client but you have to specify all things you want to use when first opening the connection.

This got me curious. How many lines of code would one need to build a GUI client that does all that on Linux. The answer turned out to be around 1500 lines of code whose job is mostly to glue together the libvte terminal emulator widget and the libssh network library. This is what it looks like:

Port forwardings can be opened at any time. This allows you to e.g. forward http traffic through your own proxy server to go around draconian firewalls.
File transfers also work.
A lot of things do not work, such as reverse port forwards or changing the remote directory in file transfers. Some key combinations that have ctrl/alt/etc modifiers can't be sent over the terminal. I don't really know why, but it seems the vte terminal does some internal state tracking to know which modifiers are active. There does not seem to be a way to smuggle corresponding raw keycodes out, it seems to send them directly to the terminal it usually controls. I also did not find an easy way of getting full keyboard status from raw GTK+ events.

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