qemu-resize.py

#!/usr/bin/env python3
"""
My QEMU SDL window resizes itself to the correct size for its guest display, then forgets about that size for some reason when it loses focus. This script restores the window so its content size is as specified.

See sway-ipc(7) for protocol and message ids/formats.
"""

import json
import os
import socket
import struct
import sys


MAGIC = b"i3-ipc"
HEADER = struct.Struct("=6xII")
RUN_COMMAND = 0
GET_TREE = 4

TARGET_APP_ID = "qemu-system-x86_64"
TARGET_WIDTH = 1440
TARGET_HEIGHT = 900


def format_message(type_id, payload):
	buf = bytearray(HEADER.size + len(payload))
	HEADER.pack_into(buf, 0, len(payload), type_id)
	buf[:len(MAGIC)] = MAGIC
	buf[HEADER.size:] = payload
	return buf


def recv_sized(sock, byte_length):
	buf = bytearray(byte_length)
	view = memoryview(buf)

	while view:
		r = sock.recv_into(view)
		view = view[r:]

		if r == 0:
			raise EOFError

	return buf


def read_message(sock):
	header_buf = recv_sized(sock, HEADER.size)

	if not header_buf.startswith(MAGIC):
		raise Exception("expected i3-ipc magic string")

	payload_len, type_id = HEADER.unpack(header_buf)

	payload_buf = recv_sized(sock, payload_len)

	return (type_id, payload_buf)


def walk(root):
	stack = [root]

	while stack:
		node = stack.pop()
		yield node
		stack.extend(node["nodes"])
		stack.extend(node["floating_nodes"])


def main():
	with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as sock:
		sock.connect(os.environb[b"SWAYSOCK"])

		sock.sendall(format_message(GET_TREE, b""))
		_, tree_json = read_message(sock)
		tree = json.loads(tree_json)
		target_node = next((node for node in walk(tree) if node.get("app_id") == TARGET_APP_ID), None)

		if target_node is None:
			print(f"No node with target app_id {TARGET_APP_ID!r} found.", file=sys.stderr)
			raise SystemExit(1)

		dw = (
			target_node["rect"]["width"]
			- target_node["window_rect"]["width"]
		)
		dh = (
			target_node["rect"]["height"]
			+ target_node["deco_rect"]["height"]
			- target_node["window_rect"]["height"]
		)

		sock.sendall(
			format_message(
				RUN_COMMAND,
				b"[app_id=%s] resize set width %d px height %d px" % (
					TARGET_APP_ID.encode(),
					TARGET_WIDTH + dw,
					TARGET_HEIGHT + dh,
				),
			)
		)
		_, response_json = read_message(sock)

	print(json.loads(response_json))


if __name__ == "__main__":
	main()