PulseAudio 'System Events' volume knob

knob.c

#if 0
pkg = libpulse
src = $(MAKEFILE_LIST)
app = $(basename $(src))

CFLAGS  = $(shell pkg-config --cflags $(pkg)) -x c
LDFLAGS = $(shell pkg-config --libs $(pkg))

$(app): $(src)

define source
#endif

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>

#include <pulse/mainloop.h>
#include <pulse/ext-stream-restore.h>

#include <err.h>

void adjust_stream(pa_mainloop *loop, pa_context *ctx,
                   char *name, unsigned value, bool mute)
{
	pa_volume_t vol;
	pa_ext_stream_restore_info info;
	pa_operation *o;

	vol = (value * PA_VOLUME_NORM) / 100;

	info = (pa_ext_stream_restore_info) {
		.name = name,
		.channel_map = {
			.channels = 1,
			.map = { PA_CHANNEL_POSITION_MONO },
		},
		.volume = {
			.channels = 1,
			.values = { mute ? PA_VOLUME_MUTED : vol },
		},
		.device = "",
		.mute = mute,
	};

	//assert(pa_cvolume_compatible_with_channel_map(&info.volume, &info.channel_map));

	o = pa_ext_stream_restore_write(ctx, PA_UPDATE_REPLACE, &info, 1,
					true, NULL, NULL);
	if (!o)
		errx(1, "pa_ext_stream_restore_write failed");

	pa_mainloop_iterate(loop, 1, NULL);
}

void try_connect(pa_mainloop *loop, pa_context *ctx) {
	if (pa_context_connect(ctx, NULL, PA_CONTEXT_NOFAIL, NULL) < 0)
		errx(1, "connection to PulseAudio failed");

	for (;;) {
		pa_mainloop_iterate(loop, 1, NULL);
		switch (pa_context_get_state(ctx)) {
		case PA_CONTEXT_READY:
			return;
		case PA_CONTEXT_FAILED:
			errx(1, "handshake with PulseAudio failed");
			return;
		}
	}
}

void pa_main(unsigned percent, bool muted) {
	pa_mainloop *loop;
	pa_context *ctx;

	loop = pa_mainloop_new();
	ctx = pa_context_new(pa_mainloop_get_api(loop), "knob");

	try_connect(loop, ctx);
	adjust_stream(loop, ctx, "sink-input-by-media-role:event", percent, muted);

	pa_context_unref(ctx);
	pa_mainloop_free(loop);
}

int main(int argc, char *argv[]) {
	unsigned long percent = 0;
	bool muted = false;

	if (argc != 2)
		errx(1, "missing volume level argument");
	
	percent = strtoul(argv[1], NULL, 10);

	pa_main(percent, muted);

	return 0;
}

#if 0
endef
#endif