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GjsPipe

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GjsPipe provides utilities to safely manage your Gio.Subprocess.

The library provides a Pipe class for easily and safely creating processes in your gjs application and consuming the process output line by line.

Basic Usage

    // define a process to run a script in your system
    let p = new Pipe('bash', '-c', 'while sleep 1; do echo "looping"; done')

    // start the process and start reading output line by line
    let cancel = p.start(line => print(line))

    // if required, stop the pipe using the cancel function
    cancel()

    // That's all!

WARNING: Make sure to call cancel before exiting your gjs app.

An unclean exit of your gjs app can create orphaned processes in your system. Unfortunately gjs does not ensure that all instances of Gio.Subprocess are killed automatically on program exit.

Complete Usage Example

Here is an example how to turn a system program on and off and consume its output.

    const script = 'my-command'
    const p = new Pipe('bash', '-c', script)
    let cancel = null

    function onResult(line) {
        print(line)
    }

    function onExit(ok) {
        if (ok) log(`pipe ${script} stopped`)
        else    logError(new Error(`pipe ${script} failed, see logs for details`))
    }

    function onError(err) {
        logError(err)
        if (cancel) {
            log(`pipe ${script} had errors, stopping pipe...`)
            cancel()
        }
    }

    function startPipe() {
        return p.start(onResult, onExit, onError)
    }

    function toggle() {
        if (cancel) { cancel(); cancel = null }
        else        { cancel = startPipe()    }
    }

    toggleBtn.connect('toggled', (btn) => toggle())

The onExit and onError callbacks are optional.

Without onError any errors will be logged via logError.
Without onExit the pipe may exit and fail silently.

Async Features

In addition to two simple asyncTimeout and makeAsync functions for running and awaiting any function asynchronously, this library also provides a glibAsync function to await async Glib start and finish calls.

Async Execution of Gio/GLib Functions

Async Gio and Glib functions usually consist of a <func>_async and a <func>_finish for calling and handling async IO. They do not return a Promise and thus cannot be awaited.

GjsPipe provides glibAsync to mitigate this.

Instead of callback-based execution, where errors may get lost in async nirvana:

const ctx = new Gio.Cancellable()
try {
    proc.wait_check_async(ctx, (_, res) => {
        try {
            const ok = proc.wait_check_finish(res)
        } catch (e) {
            // async errors must be handled in the async handler functions
            // and somehow be exposed the start-level using another callback
            handleAsyncError(e)
        }
    }
} catch (e) {
    // only "start" errors can be catched
}

You can now use async and await and have errors thrown to where you started the execution:

try {
    const ctx = new Gio.Cancellable()
    const ok = await glibAsync(
        (finish) => proc.wait_check_async(ctx, finish),  // GLib start logic
        (_, res) => proc.wait_check_finish(res),         // GLib finish logic
    )
} catch (e) {
    // all errors can handled at the start-level of the async function
}