wpiutil: Add C++ libuv wrappers (#1166)

- Provide an EventLoopRunner to run uv::Loop on a separate thread.

- Add raw_ostream wrapper for uv::Buffer.

wpiutil/src/main/native/include/wpi/uv/Buffer.h

@@ -0,0 +1,92 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018 FIRST. 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#ifndef WPIUTIL_WPI_UV_BUFFER_H_
+#define WPIUTIL_WPI_UV_BUFFER_H_
+
+#include <uv.h>
+
+#include <cstring>
+#include <initializer_list>
+#include <utility>
+
+#include "wpi/ArrayRef.h"
+#include "wpi/StringRef.h"
+
+namespace wpi {
+namespace uv {
+
+/**
+ * Data buffer.  Convenience wrapper around uv_buf_t.
+ */
+class Buffer : public uv_buf_t {
+ public:
+  Buffer() {
+    base = nullptr;
+    len = 0;
+  }
+  /*implicit*/ Buffer(const uv_buf_t& oth) {  // NOLINT(runtime/explicit)
+    base = oth.base;
+    len = oth.len;
+  }
+  /*implicit*/ Buffer(StringRef str)  // NOLINT(runtime/explicit)
+      : Buffer{str.data(), str.size()} {}
+  /*implicit*/ Buffer(ArrayRef<uint8_t> arr)  // NOLINT(runtime/explicit)
+      : Buffer{reinterpret_cast<const char*>(arr.data()), arr.size()} {}
+  Buffer(char* base_, size_t len_) {
+    base = base_;
+    len = len_;
+  }
+  Buffer(const char* base_, size_t len_) {
+    base = const_cast<char*>(base_);
+    len = len_;
+  }
+
+  ArrayRef<char> data() const { return ArrayRef<char>{base, len}; }
+  MutableArrayRef<char> data() { return MutableArrayRef<char>{base, len}; }
+
+  operator ArrayRef<char>() const { return data(); }
+  operator MutableArrayRef<char>() { return data(); }
+
+  static Buffer Allocate(size_t size) { return Buffer{new char[size], size}; }
+
+  static Buffer Dup(StringRef in) {
+    Buffer buf = Allocate(in.size());
+    std::memcpy(buf.base, in.data(), in.size());
+    return buf;
+  }
+
+  static Buffer Dup(ArrayRef<uint8_t> in) {
+    Buffer buf = Allocate(in.size());
+    std::memcpy(buf.base, in.begin(), in.size());
+    return buf;
+  }
+
+  void Deallocate() {
+    delete[] base;
+    base = nullptr;
+    len = 0;
+  }
+
+  Buffer Move() {
+    Buffer buf = *this;
+    base = nullptr;
+    len = 0;
+    return buf;
+  }
+
+  friend void swap(Buffer& a, Buffer& b) {
+    using std::swap;
+    swap(a.base, b.base);
+    swap(a.len, b.len);
+  }
+};
+
+}  // namespace uv
+}  // namespace wpi
+
+#endif  // WPIUTIL_WPI_UV_BUFFER_H_