[wpiutil, wpilib] Add FileLogger and log console output (#6977)

wpiutil/src/main/native/include/wpi/FileLogger.h

@@ -0,0 +1,61 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <functional>
+#include <string_view>
+#include <thread>
+
+#include "wpi/DataLog.h"
+
+namespace wpi {
+/**
+ * A class version of `tail -f`, otherwise known as `tail -f` at home.  Watches
+ * a file and puts the data somewhere else. Only works on Linux-based platforms.
+ */
+class FileLogger {
+ public:
+  FileLogger() = default;
+  /**
+   * Construct a FileLogger. When the specified file is modified, the callback
+   * will be called with the appended changes.
+   *
+   * @param file The path to the file.
+   * @param callback A callback that accepts the appended file data.
+   */
+  FileLogger(std::string_view file,
+             std::function<void(std::string_view)> callback);
+
+  /**
+   * Construct a FileLogger. When the specified file is modified, appended data
+   * will be appended to the specified data log.
+   *
+   * @param file The path to the file.
+   * @param log A data log.
+   * @param key The log key to append data to.
+   */
+  FileLogger(std::string_view file, log::DataLog& log, std::string_view key);
+  FileLogger(FileLogger&& other);
+  FileLogger& operator=(FileLogger&& rhs);
+  ~FileLogger();
+  /**
+   * Creates a function that chunks incoming data into lines before calling the
+   * callback with the individual line.
+   *
+   * @param callback The callback that logs lines.
+   * @return The function.
+   */
+  static std::function<void(std::string_view)> LineBuffer(
+      std::function<void(std::string_view)> callback);
+
+ private:
+#ifdef __linux__
+  int m_fileHandle = -1;
+  int m_inotifyHandle = -1;
+  int m_inotifyWatchHandle = -1;
+  std::thread m_thread;
+#endif
+};
+}  // namespace wpi