#!/usr/bin/env python3
# SPDX-License-Identifier: GPL-3.0-only
"""Print textual metadata from a PNG file."""

import struct, sys

with open(sys.argv[1], "rb") as source:
    if source.read(8) != b"\x89PNG\r\n\x1a\n":
        raise SystemExit("not a PNG")
    while True:
        header = source.read(8)
        if len(header) != 8:
            raise SystemExit("truncated PNG")
        length, kind = struct.unpack(">I4s", header)
        data = source.read(length)
        if len(data) != length or len(source.read(4)) != 4:
            raise SystemExit("truncated PNG")
        if kind == b"tEXt":
            key, _, value = data.partition(b"\0")
            print(key.decode("latin-1") + "=" + value.decode("latin-1"))
        if kind == b"IEND":
            break