Lua script read from serial port in OpenWRT - lua

Question

I have Openwrt router with Arduino connected via USB FTDI adapter.
Serial port is /dev/ttyUSB0
Arduino code prints some data:
First part of data printed with delay via command print(), for example:
Serial.begin(9600);
Serial.print(var1);
delay(1000);
Serial.print(var2);
delay(1000);
Serial.print(var3);
delay(1000);
And second part printed with println() command:
Serial.println("");
Serial.println(var4);
Serial.println(var5);
Serial.println(var6);
So when I open Serial port in terminal I can see something like this:
1
then timeout in 1 sec, then
1 2
next timeout. and then
1 2 3
last timeout and
1 2 3
4
5
6
It works in Terminal program and in console in OpenWRT, for example screen /dev/ttyUSB0
I need make a Lua script that will read Serial port and print the data in the same way. I have a simple script, but it doesn't work as expected.
rserial=io.open("/dev/ttyUSB0","r")
while true do
chain = nil
while chain==nil do
chain=rserial:read();
print(chain)
end
end
it shows all data at once.
it doesn't show first 3 vars one by one with delays.
Seems it is because of rserial:read() - it will read until it receives a newline character.
It stated in similar question:
How to read from a serial port in lua
I tried to run this command as was advised there:
stty -F /dev/ttyUSB0 -icanon
but it doesn't help and I don't understand why.
Is it the way to fix this behavior via stty?
or I definitely need to use another Serial libs for Lua script?
All of these libs seems pretty outdated for now and I don't want to use outdated stuff..

Answer 1

From the Lua Reference Manual:
When called without formats, it uses a default format that reads the
next line (see below).
A new line is anything in the buffer until the next newline character.
So as long as you don't send a newline character Lua will wait one as it has been told by calling read()
Once a newline character is received you will be prompted any other character in that line.
Terminal programs usually update every byte to show what they receive in "real-time".
So if you want to have the same behaviour you may not use read() without any arguments.
Use read(1) to read every single byte without waiting for anything else.