Decode AmneziaWG client key in Java

decode.java

public static class Decoder {
  
	public void test() throws Exception {
    // AmneziaWG client key which starts with "vpn://" is just a Base64 encoded and compressed JSON configuration file
		final var encoded = "vpn://<insert your client key>".replace("vpn://", "");
    // They use Base64 URL encoder. Inside of the Base64 encoded string is a compressed data.
		final var compressed = ByteBuffer.wrap(Base64.getUrlDecoder().decode(encoded));
    // Data is compressed using QT qCompress function, which uses zlib and adds a 4 byte header to the compressed data
		final var header = new byte[4]; // The header is 32-bit unsigned integer representing the size of uncompressed data
		compressed.get(header); // This will remove 4 byte header from the buffer
		
		final var inflater = new Inflater();
		inflater.setInput(compressed);
    // 10 KB should be enough to fit uncompressed data because configs are quite small. Increase if needed.
		final var uncompressed = ByteBuffer.allocate(1024 * 10);
		inflater.inflate(uncompressed);
		uncompressed.flip(); // After data is written to the buffer, flip the buffer so we can start reading from it
		
		final var data = new byte[uncompressed.remaining()];
		uncompressed.get(data);
		final var text = new String(data);
		System.out.println(text); // This will print the entire AmneziaWG client configuration
		
    // JsonObject is from the Vertx.io library (you can use any other JSON library)
		final var lastConfig = new JsonObject(text)
			.getJsonArray("containers") // Different connection protocols they call "containers"
			.getJsonObject(0)
			.getJsonObject("awg") // "awg" is for the AmneziaWG connection protocol
			.getString("last_config");
		System.out.println(lastConfig); // This will be the specific configuration for awg protocol
	} 

}