Gio.DataInputStream.prototype.read_line_finish

function read_line_finish(result: Gio.AsyncResult): [return_value: ByteArray, length: Number(gsize)] {
    // Gjs wrapper for g_data_input_stream_read_line_finish()
}

Finish an asynchronous call started by Gio.DataInputStream.prototype.read_line_async. Note the warning about string encoding in Gio.DataInputStream.prototype.read_line applies here as well.

Since 2.20

result: the Gio.AsyncResult that was provided to the callback.
return_value: a NUL-terminated byte array with the line that was read in (without the newlines). Set length to a #gsize to get the length of the read line. On an error, it will return null and @error will be set. If there's no content to read, it will still return null, but @error won't be set.
length: a #gsize to get the length of the data read in.