Opening new pseudo-terminal device file in macOS with swift

Question

I am trying to keep a shell (bash/zsh/etc) running by using Process from the Foundation library.

I know how to use Pipe for standard input/output/error for other command line executables but it seems like the shell programs require that the standard input/output/error file be a terminal device file.

It looks like these are the files called /dev/ttys<3 digit number> which are created for every new shell instance. How can I create these files myself and use them in swift?

Answer 1

SOLUTION:

So this turned out to be a lot easier than I thought it would be. Here are the steps needed to create a pair of master and slave pseudo-terminal FileHandle objects:

1. Import the Darwin module.
2. Call on posix_openpt(int oflag) to get a file descriptor for an available master pseudo-terminal device.
3. Call on grantpt(int filedes) to establish ownership of corresponding slave pseudo-terminal device.
4. Call on unlockpt(int filedes) to unlock the slave pseudo-terminal device.
5. Call on ptsname(int filedes) to get path to slave pseudo-terminal device.
6. Create FileHandle objects using the file descriptor from step 2 and path from step 5.

In steps 3 - 5 filedes is the file descriptor returned by the call to posix_openpt(int oflag) from step 1. Use O_RDRW for the oflag parameter in step 1 for read-write permissions on the master pseudo-terminal device file.

Example code where we keep a bash session alive and have it run the tty command:

import Foundation
import Darwin

class A: NSObject {
    var task: Process?
    var slaveFile: FileHandle?
    var masterFile: FileHandle?

    override init() {
        self.task = Process()
        var masterFD: Int32 = 0
        masterFD = posix_openpt(O_RDWR)
        grantpt(masterFD)
        unlockpt(masterFD)
        self.masterFile = FileHandle.init(fileDescriptor: masterFD)
        let slavePath = String.init(cString: ptsname(masterFD))
        self.slaveFile = FileHandle.init(forUpdatingAtPath: slavePath)
        self.task!.executableURL = URL(fileURLWithPath: "/bin/bash")
        self.task!.arguments = ["-i"]
        self.task!.standardOutput = slaveFile
        self.task!.standardInput = slaveFile
        self.task!.standardError = slaveFile
    }

    func run() {
        DispatchQueue.global(qos: .userInitiated).async { [weak self] in
            guard let self = self else {
                return
            }
            do {
                try self.task!.run()
            } catch {
                print("Something went wrong.\n")
            }
        }
        let data = self.masterFile!.availableData
        let strData = String(data: data, encoding: String.Encoding.utf8)!
        print("Output: "+strData)
        self.masterFile!.write("tty\u{0D}".data(using: String.Encoding.utf8)!)
        sleep(1)
        let data1 = self.masterFile!.availableData
        let strData1 = String(data: data1, encoding: String.Encoding.utf8)!
        print("Output: "+strData1)
    }
}

let a = A()
a.run()