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/cpp/uv/GetAddrInfo.cpp

@@ -0,0 +1,55 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "wpi/uv/GetAddrInfo.h"
+
+#include "wpi/uv/Loop.h"
+#include "wpi/uv/util.h"
+
+namespace wpi {
+namespace uv {
+
+GetAddrInfoReq::GetAddrInfoReq() {
+  error = [this](Error err) { GetLoop().error(err); };
+}
+
+void GetAddrInfo(Loop& loop, const std::shared_ptr<GetAddrInfoReq>& req,
+                 const Twine& node, const Twine& service,
+                 const addrinfo* hints) {
+  SmallVector<char, 128> nodeStr;
+  SmallVector<char, 128> serviceStr;
+  int err = uv_getaddrinfo(
+      loop.GetRaw(), req->GetRaw(),
+      [](uv_getaddrinfo_t* req, int status, addrinfo* res) {
+        auto& h = *static_cast<GetAddrInfoReq*>(req->data);
+        if (status < 0)
+          h.ReportError(status);
+        else
+          h.resolved(*res);
+        uv_freeaddrinfo(res);
+        h.Release();  // this is always a one-shot
+      },
+      node.isNull() ? nullptr : node.toNullTerminatedStringRef(nodeStr).data(),
+      service.isNull() ? nullptr
+                       : service.toNullTerminatedStringRef(serviceStr).data(),
+      hints);
+  if (err < 0)
+    loop.ReportError(err);
+  else
+    req->Keep();
+}
+
+void GetAddrInfo(Loop& loop, std::function<void(const addrinfo&)> callback,
+                 const Twine& node, const Twine& service,
+                 const addrinfo* hints) {
+  auto req = std::make_shared<GetAddrInfoReq>();
+  req->resolved.connect(callback);
+  GetAddrInfo(loop, req, node, service, hints);
+}
+
+}  // namespace uv
+}  // namespace wpi