Dynamically update the greeter text

[mjkloeckner]

Closes #234

Description

Adds new flag: --greeter-cmd, which accepts a command name to execute and set the output as the greeter text.

This new flag conflicts with --greeter-text because the output from the command overrides the variable containing the greeter text passed with --greeter-text, so they can't be used together.

If the indicator is idle, the greeter gets updated every second, if the user is typing, the greeter gets updated at every key press, this could lead to performance issues?

Alternative

The function that updates the greeter text executes the expression passed by --greeter-cmd this can lead to erratic behavior if the user isn't careful enough, for example if the user passes the i3lock invocation script as the argument it can lead to a fork bomb.

void update_greeter_text() {
    FILE *fp;
    static char file_text[128];

    memset(file_text,0,sizeof(file_text));

    DEBUG("greeter_cmd is: [%s]\n", greeter_cmd);
    if((fp = popen(greeter_cmd, "r")) == NULL)
        return;

    fread(file_text, sizeof(char), sizeof(file_text), fp);
    pclose(fp);

    greeter_text = file_text;
}

An alternative implementation of this function would be using a temporary file for example /tmp/i3lock-greeter-text and updating the greeter text based on the contents of this file. Maybe this would be a better solution?

Screenshots/screencaps

In this example I plug the power cord and the battery icon updates:

In the screencap I invoke i3lock with these flags:

$ i3lock -c 00000000 --wrong-text="" --lock-text="" --lockfailed-text="" \
        --verif-text="" --verif-text="" --noinput-text="" \
        -i $HOME/.cache/wall_dimblur.png \
        -M --pointer default -k \
        --time-str="%H:%M" --time-size=110 \
        --time-font="Segoe UI Variable Static Display:style=Semibold" \
        --time-pos="ix:iy - 142" --time-color="FFFFFFCC" \
        --date-str="%A, %B %d" --date-size=26 \
        --date-font="Segoe UI Variable Static Display:style=Semibold" \
        --date-pos="tx:ty + 35 + 1" --date-color="FFFFFFCC" \
        --bar-indicator --bar-direction 2 --bar-color 00000000 --bar-pos "h" \
        --bar-step 6 --bar-max-height 6 --bar-periodic-step 6 \
        --keyhl-color="736654CC" -e -n \
        --greeter-pos="tx:ty + 70" \
        --greeter-color="FFFFFFCC" --greeter-font="CaskaydiaCove Nerd Font" \
        --greeter-size=20 --greeter-cmd="lockscreen-greeter"

Being lockscreen-greeter a script which contains:

#!/bin/sh

battery=$(battery-percentage-nerd-font)
kbmap=$(setxkbmap -query | grep -oP 'layout:\s*\K\w+')

printf "%s 󰇙 󰌌 %s" "$battery" "$kbmap"

Release notes

Notes: no-notes.