💚 Fix stdout interception

MasKitTests/Commands/InfoCommandSpec.swift

@@ -60,11 +60,11 @@ class InfoCommandSpec: QuickSpec {
                 let result = cmd.run(InfoCommand.Options(appId: result.trackId.description))
 
                 expect(result).to(beSuccess())
-                waitUntil { done in
-                    print(output.contents)
-                    expect(output.contents) == expectedOutput
-                    done()
-                }
+                // output is async so need to wait for contents to be updated
+                expect(output.contents).toNotEventually(beEmpty())
+                expect(output.contents) == expectedOutput
+
+                output.closeConsolePipe()
             }
         }
     }

MasKitTests/OutputListener.swift

@@ -6,60 +6,76 @@
 //  Copyright © 2019 mas-cli. All rights reserved.
 //
 
+import XCTest
 import Foundation
 
+/// Test helper for monitoring strings written to stdout. Modified from:
 /// https://medium.com/@thesaadismail/eavesdropping-on-swifts-print-statements-57f0215efb42
 class OutputListener {
-    // open a new Pipe to consume the messages on STDOUT and STDERR
+    /// consumes the messages on STDOUT
     let inputPipe = Pipe()
 
-    // open another Pipe to output messages back to STDOUT
+    /// outputs messages back to STDOUT
     let outputPipe = Pipe()
 
+    /// Buffers strings written to stdout
     var contents = ""
 
+    /// Sets up the "tee" of piped output, intercepting stdout then passing it through.
+    ///
+    /// ## [dup2 documentation](https://linux.die.net/man/2/dup2)
+    /// `int dup2(int oldfd, int newfd);`
+    /// `dup2()` makes `newfd` be the copy of `oldfd`, closing `newfd` first if necessary.
     func openConsolePipe() {
-        let pipeReadHandle = inputPipe.fileHandleForReading
+        // Set up a read handler which fires when data is written to our inputPipe
+        inputPipe.fileHandleForReading.readabilityHandler = { [weak self] fileHandle in
+            guard let strongSelf = self else { return }
 
-        //from documentation
-        //dup2() makes newfd (new file descriptor) be the copy of oldfd (old file descriptor), closing newfd first if necessary.
+            let data = fileHandle.availableData
+            if let string = String(data: data, encoding: String.Encoding.utf8) {
+                strongSelf.contents += string
+            }
 
-        //here we are copying the STDOUT file descriptor into our output pipe's file descriptor
-        //this is so we can write the strings back to STDOUT, so it can show up on the xcode console
-        dup2(STDOUT_FILENO, outputPipe.fileHandleForWriting.fileDescriptor)
+            // Write input back to stdout
+            strongSelf.outputPipe.fileHandleForWriting.write(data)
+        }
 
-        //In this case, the newFileDescriptor is the pipe's file descriptor and the old file descriptor is STDOUT_FILENO and STDERR_FILENO
+        var dupStatus: Int32
 
-        dup2(inputPipe.fileHandleForWriting.fileDescriptor, STDOUT_FILENO)
-        dup2(inputPipe.fileHandleForWriting.fileDescriptor, STDERR_FILENO)
+        // Copy STDOUT file descriptor to outputPipe for writing strings back to STDOUT
+        dupStatus = dup2(stdoutFileDescriptor, outputPipe.fileHandleForWriting.fileDescriptor)
+        // Status should equal newfd
+        assert(dupStatus == outputPipe.fileHandleForWriting.fileDescriptor)
 
-        //listen in to the readHandle notification
-        NotificationCenter.default.addObserver(self, selector: #selector(self.handlePipeNotification), name: FileHandle.readCompletionNotification, object: pipeReadHandle)
+        // Intercept STDOUT with inputPipe
+        // newFileDescriptor is the pipe's file descriptor and the old file descriptor is STDOUT_FILENO and STDERR_FILENO
+        dupStatus = dup2(inputPipe.fileHandleForWriting.fileDescriptor, stdoutFileDescriptor)
+        // Status should equal newfd
+        assert(dupStatus == stdoutFileDescriptor)
 
-        //state that you want to be notified of any data coming across the pipe
-        pipeReadHandle.readInBackgroundAndNotify()
+        // Don't have any tests on stderr yet
+        // dup2(inputPipe.fileHandleForWriting.fileDescriptor, stderr)
     }
 
-    @objc func handlePipeNotification(notification: Notification) {
-        //note you have to continuously call this when you get a message
-        //see this from documentation:
-        //Note that this method does not cause a continuous stream of notifications to be sent. If you wish to keep getting notified, you’ll also need to call readInBackgroundAndNotify() in your observer method.
-        inputPipe.fileHandleForReading.readInBackgroundAndNotify()
+    /// Tears down the "tee" of piped output.
+    func closeConsolePipe() {
+        // Restore stdout
+        freopen("/dev/stdout", "a", stdout)
 
-        if let userInfo = notification.userInfo,
-            let data = userInfo[NSFileHandleNotificationDataItem] as? Data,
-            let str = String(data: data, encoding: String.Encoding.ascii) {
-
-            contents += str
-
-            //write the data back into the output pipe. the output pipe's write file descriptor points to STDOUT. this allows the logs to show up on the xcode console
-            outputPipe.fileHandleForWriting.write(data)
-
-            // `str` here is the log/contents of the print statement
-            //if you would like to route your print statements to the UI: make
-            //sure to subscribe to this notification in your VC and update the UITextView.
-            //Or if you wanted to send your print statements to the server, then
-            //you could do this in your notification handler in the app delegate.
+        [inputPipe.fileHandleForReading, outputPipe.fileHandleForWriting].forEach { file in
+            file.closeFile()
         }
     }
 }
+
+extension OutputListener {
+    /// File descriptor for stdout (aka STDOUT_FILENO)
+    var stdoutFileDescriptor: Int32 {
+        return FileHandle.standardOutput.fileDescriptor
+    }
+
+    /// File descriptor for stderr (aka STDERR_FILENO)
+    var stderrFileDescriptor: Int32 {
+        return FileHandle.standardError.fileDescriptor
+    }
+}