From Xcode, how do I read data from a text file that is constantly being updated?

Question

Hello,

I'm working with a GPS module that is transferring data to my mac over a serial RS232-to-USB interface. I've written a objC program that takes the raw data and converts it into meaningful information.

Using a program called goSerial, I'm able to log all incoming data into a text file. I have been able to make my program read the text file and process data line by line.

I would like this procedure to happen in real time i.e. as soon as the data is received, it gets logged into the text file and my program reads it. The first part of this happens automatically that is the text file is being constantly appended (when not open). Is it possible to monitor a text file for appended data and only read new lines? Also, will doing this affect the ability of new incoming data to be saved?

Thanks!!!

(Also, if anyone knows how I may send serial data directly to Xcode, please let me know!)

Answer 1

You should be able to create a unix domain socket, which you can then have your goSerial application open (as it looks like a normal file on the fs)

And then read from the other end, linewise in your application. This is probably the easiest way, or alternately have a look at the source of tail in GNU's coreutils, specifically it's -f function (although thinking more you'll probably want to look at how the FreeBSD implementation works, as I believe that the GNU version uses some linux specific callback)

Answer 2

You can use a kqueue (perhaps with a wrapper such as UKKQueue) to watch the file for changes.

Answer 3

I'm not sure how the serial-to-USB affects things but traditionally, unix accesses serial devices using the Device-File Mechanism which treats the input from the device as a file to be read. You would use NSFileHandle to read the file from Cocoa/Foundation. You probably want to checkout the IORegistryExplorer app to see how your device shows up.