Adds wpi GetHostname function (#25)

src/main/native/cpp/support/hostname.cpp

@@ -0,0 +1,64 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2017. 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "support/hostname.h"
+
+#ifdef _WIN32
+#include <Winsock2.h>
+#pragma comment(lib, "Ws2_32.lib")
+#else
+#include <unistd.h>
+#endif
+
+#include <string>
+#include "llvm/SmallVector.h"
+#include "llvm/StringRef.h"
+
+#ifdef _WIN32
+struct WSAHelper {
+  WSAHelper() {
+    WSAData wsaData;
+    WORD wVersionRequested = MAKEWORD(2, 2);
+    WSAStartup(wVersionRequested, &wsaData);
+  }
+  ~WSAHelper() { WSACleanup(); }
+};
+
+static WSAHelper& GetWSAHelper() {
+  static WSAHelper helper;
+  return helper;
+}
+#endif
+
+namespace wpi {
+static bool GetHostnameImpl(char* name, size_t name_len) {
+#ifdef _WIN32
+  GetWSAHelper();
+#endif
+  if (::gethostname(name, name_len) != 0) return false;
+  name[name_len - 1] = '\0'; // Per POSIX, may not be null terminated if too long
+  return true;
+}
+
+std::string GetHostname() {
+  char name[256];
+  if (!GetHostnameImpl(name, sizeof(name))) return "";
+  return name;
+}
+
+llvm::StringRef GetHostname(llvm::SmallVectorImpl<char>& name) {
+  // Use a tmp array to not require the SmallVector to be too large.
+  char tmpName[256];
+  if (!GetHostnameImpl(tmpName, sizeof(tmpName))) {
+    return llvm::StringRef{};
+  }
+  name.clear();
+  name.append(tmpName, tmpName + std::strlen(tmpName) + 1);
+
+  return llvm::StringRef{name.data(), name.size(), true};
+}
+}  // namespace wpi