onKeyPressed doesn't listen for modified (e.g. ctrl-u, alt-a, etc.) characters

[stephentalley]

Our app has a need to listen to various control-modified keys (ctrl-u, ctrl-f, ctrl-b, etc.). But:

session {
    var keyPressed by liveVarOf<Key?>(null)
    section {
        if (keyPressed != null) {
            textLine("key pressed: $keyPressed")
        }
    }.runUntilKeyPressed(Keys.Q, Keys.ESC) {
        onKeyPressed {
            keyPressed = key
        }
    }
}

…shows those keys are ignored.

Is there an API to listen for those keys?

• OS: Linux
• Version 1.1.1

[bitspittle]

I don't have access to anything except that which the terminal gives me. So depending on what you're expecting, it's probably not possible. See also: #57 in case it's related.

I wonder if you could write a raw console app, just like a naked main function and use of readLine, and see if you're getting characters in that case.

[bitspittle]

A user on my Discord just pointed out that Mordant has rich support for raw keypresses. Taking notes here.

• At a high level, you have the enterRawMode interface method

• Here's the default JVM implementation, which throws an unsupported error.

Mordant actually supports three implementations that apparently supply raw mode logic.

• Java Foreign Functions and Memory APIs. Requires JDK22+
• JNA. Flexible solution but a bundled native library increases the JAR size
  • See also: https://github.com/java-native-access/jna
• GraalVM FFI (but doesn't support regular JRE runtimes)

Between these three, I think JNA is the way to go. However, I'll need to investigate to see by how much the native library increases the jar size. If it's like a few MBs or less, it may be worth it just to do it. Putting the logic in a separate module doesn't seem too bad.

JNA implementation for windows

Still not sure how mac and linux work. Will investigate later.

---

If I can get this working right, I think for a first pass, I would mostly keep onKeyPressed the same, except I would add
ctrl, alt, and shift booleans. I might also see if I can generate key presses for just CTRL, ALT, and SHIFT on their own.

---

TODO:

• Figure out bundle size of native library / libraries for JNA solution
• Figure out how linux works
• Figure out how mac works
• Update Kotter

[KyleMcB]

I am using kotter to make a shell and also needed alt+n ctrl+n
I wrote my own system to collect and interpret from Terminal.read() from kotter
I'll share it here, but its super early. I wouldn't be surprised if it only works on iTerm2. probably won't work with xterm. also you have to use a runUntilSignal and collect the in the runscope.
https://github.com/KyleMcB/kross/blob/develop/kross/src/main/kotlin/com/xingpeds/kross/utf8Input.kt
my code isn't documented or tested yet sorry. Also it doesn't detect alt+ctrl+n you probably could. I hit a complexity limit before I document and refactor. See the app entry point at
https://github.com/KyleMcB/kross/blob/develop/kross/src/main/kotlin/com/xingpeds/kross/App.kt
note how I signal() and cancel the collectionScope when someone pressing enter.