Fixes SerialHelper when used with OS serial ports. (#411)

Also makes the SerialHelper API public so it can be used externally.

hal/include/HAL/cpp/SerialHelper.h

@@ -0,0 +1,51 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2016. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <stdint.h>
+
+#include <string>
+#include <vector>
+
+#include "HAL/SerialPort.h"
+#include "HAL/cpp/priority_mutex.h"
+#include "llvm/SmallString.h"
+#include "llvm/SmallVector.h"
+
+namespace hal {
+class SerialHelper {
+ public:
+  SerialHelper();
+
+  std::string GetVISASerialPortName(HAL_SerialPort port, int32_t* status);
+  std::string GetOSSerialPortName(HAL_SerialPort port, int32_t* status);
+
+  std::vector<std::string> GetVISASerialPortList(int32_t* status);
+  std::vector<std::string> GetOSSerialPortList(int32_t* status);
+
+ private:
+  void SortHubPathVector();
+  void CoiteratedSort(llvm::SmallVectorImpl<llvm::SmallString<16>>& vec);
+  void QueryHubPaths(int32_t* status);
+
+  int32_t GetIndexForPort(HAL_SerialPort port, int32_t* status);
+
+  // Vectors to hold data before sorting.
+  // Note we will most likely have at max 2 instances, and the longest string
+  // is around 12, so these should never touch the heap;
+  llvm::SmallVector<llvm::SmallString<16>, 4> m_visaResource;
+  llvm::SmallVector<llvm::SmallString<16>, 4> m_osResource;
+  llvm::SmallVector<llvm::SmallString<16>, 4> m_unsortedHubPath;
+  llvm::SmallVector<llvm::SmallString<16>, 4> m_sortedHubPath;
+
+  int32_t m_resourceHandle;
+
+  static priority_mutex m_nameMutex;
+  static std::string m_usbNames[2];
+};
+}  // namespace hal