CODEWITHSUNDEEP
swift
Matheus
Matheus

Reputation: 134

Process data that is being sent to stdout

I'm calling an AVFoundation method that is logging a lot of data to stdout and there's no option to turn this logging off.

Is it possible to write something like a middleware to process the data before sending it to stdout?

Something like this pseudocode:

Process.beforePrint( data => {
   if (data !== blackListedData) {
      print(data);
   }
});

Upvotes: 3

Views: 372

Answers (1)

Aaron Brager
Aaron Brager

Reputation: 66252

There are a number of options you can employ using the stdio functions. Here's a simple one that redirects stdout to a log file:

class StdoutFilter {
    let path: String = {
        let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
        return (paths[0] as NSString).stringByAppendingPathComponent("swift.log")
    }()

    func startFilter() {
        freopen(path, "w", stdout)
    }

    func stopFilter() {
        fclose(stdout)
    }
}

You can use this trivial implementation like this:

let filter = StdoutFilter()

print("This goes to stdout…")

filter.startFilter()

print("This gets logged to the file…")
print("Put your AVFoundation stuff here.")

filter.stopFilter()

print("And we're back to normal!")

This could be modified in a few obvious ways. You could redirect the output to /dev/null, for example. You could also try monitoring the file and applying a predicate to determine whether the filter should be started or stopped, but I think that's more complex than I have time for at the moment.

One final note: "w" in the startFilter() function will overwrite the file if it exists. Use "a" if you prefer to append an existing file.

Upvotes: 3

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