1 files changed, 168 insertions, 0 deletions
diff --git a/ios/MullvadLogging/LogFileOutputStream.swift b/ios/MullvadLogging/LogFileOutputStream.swift
new file mode 100644
index 0000000000..0ffd434c65
--- /dev/null
+++ b/ios/MullvadLogging/LogFileOutputStream.swift
@@ -0,0 +1,168 @@
+//
+//  LogFileOutputStream.swift
+//  MullvadVPN
+//
+//  Created by pronebird on 02/08/2020.
+//  Copyright © 2020 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+/// Interval used for reopening the log file descriptor in the event of failure to open it in
+/// the first place, or when writing to it.
+private let reopenFileLogInterval: TimeInterval = 5
+
+class LogFileOutputStream: TextOutputStream {
+    private let queue = DispatchQueue(label: "LogFileOutputStreamQueue", qos: .utility)
+
+    private let fileURL: URL
+    private let encoding: String.Encoding
+    private let maxBufferCapacity: Int
+
+    private var state: State = .closed {
+        didSet {
+            switch (oldValue, state) {
+            case (.opened, .waitingToReopen), (.closed, .waitingToReopen):
+                startTimer()
+
+            case (.waitingToReopen, .opened), (.waitingToReopen, .closed):
+                stopTimer()
+
+            default:
+                break
+            }
+        }
+    }
+
+    private var timer: DispatchSourceTimer?
+    private var buffer = Data()
+
+    private enum State {
+        case closed
+        case opened(FileHandle)
+        case waitingToReopen
+    }
+
+    init(fileURL: URL, encoding: String.Encoding = .utf8, maxBufferCapacity: Int = 16 * 1024) {
+        self.fileURL = fileURL
+        self.encoding = encoding
+        self.maxBufferCapacity = maxBufferCapacity
+    }
+
+    deinit {
+        stopTimer()
+    }
+
+    func write(_ string: String) {
+        queue.async {
+            self.writeNoQueue(string)
+        }
+    }
+
+    private func writeNoQueue(_ string: String) {
+        guard let data = string.data(using: encoding) else { return }
+
+        switch state {
+        case .closed:
+            do {
+                let fileHandle = try openFile()
+                state = .opened(fileHandle)
+                try write(fileHandle: fileHandle, data: data)
+            } catch {
+                bufferData(data)
+                state = .waitingToReopen
+            }
+
+        case let .opened(fileHandle):
+            do {
+                try write(fileHandle: fileHandle, data: data)
+            } catch {
+                bufferData(data)
+                state = .waitingToReopen
+            }
+
+        case .waitingToReopen:
+            bufferData(data)
+        }
+    }
+
+    @discardableResult private func write(fileHandle: FileHandle, data: Data) throws -> Int {
+        let bytesWritten = data.withUnsafeBytes { buffer -> Int in
+            guard let ptr = buffer.baseAddress else { return 0 }
+
+            return Darwin.write(fileHandle.fileDescriptor, ptr, buffer.count)
+        }
+
+        if bytesWritten == -1 {
+            let code = POSIXErrorCode(rawValue: errno)!
+            throw POSIXError(code)
+        } else {
+            return bytesWritten
+        }
+    }
+
+    private func openFile() throws -> FileHandle {
+        let oflag: Int32 = O_WRONLY | O_CREAT
+        let mode: mode_t = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH
+
+        let fd = fileURL.path.withCString { Darwin.open($0, oflag, mode) }
+
+        if fd == -1 {
+            let code = POSIXErrorCode(rawValue: errno)!
+            throw POSIXError(code)
+        } else {
+            return FileHandle(fileDescriptor: fd, closeOnDealloc: true)
+        }
+    }
+
+    private func startTimer() {
+        timer?.cancel()
+
+        let timer = DispatchSource.makeTimerSource(queue: queue)
+        timer.setEventHandler { [weak self] in
+            self?.reopenFile()
+        }
+        timer.schedule(
+            wallDeadline: .now() + reopenFileLogInterval,
+            repeating: reopenFileLogInterval
+        )
+        timer.activate()
+
+        self.timer = timer
+    }
+
+    private func stopTimer() {
+        timer?.cancel()
+        timer = nil
+    }
+
+    private func reopenFile() {
+        do {
+            let fileHandle = try openFile()
+
+            // Write a message indicating that the file was reopened.
+            let messageData =
+                "<Log file re-opened after failure. Buffered \(buffer.count) bytes of messages>\n"
+                    .data(using: encoding, allowLossyConversion: true)!
+            try write(fileHandle: fileHandle, data: messageData)
+
+            // Write all buffered messages.
+            if !buffer.isEmpty {
+                try write(fileHandle: fileHandle, data: buffer)
+                buffer.removeAll()
+            }
+
+            state = .opened(fileHandle)
+        } catch {
+            state = .waitingToReopen
+        }
+    }
+
+    private func bufferData(_ data: Data) {
+        buffer.append(data)
+
+        if buffer.count > maxBufferCapacity {
+            buffer.removeFirst(buffer.count - maxBufferCapacity)
+        }
+    }
+}