Add Reuse function to uv::Tcp (#1208)

This allows reusing the Tcp object in cases when the connection errors out.

wpiutil/src/main/native/cpp/uv/Tcp.cpp

@@ -25,6 +25,26 @@ std::shared_ptr<Tcp> Tcp::Create(Loop& loop, unsigned int flags) {
   return h;
 }
 
+void Tcp::Reuse(std::function<void()> callback, unsigned int flags) {
+  if (!IsClosing()) {
+    m_reuseData = std::make_unique<ReuseData>();
+    m_reuseData->callback = callback;
+    m_reuseData->flags = flags;
+    uv_close(GetRawHandle(), [](uv_handle_t* handle) {
+      Tcp& h = *static_cast<Tcp*>(handle->data);
+      if (!h.m_reuseData) return;  // just in case
+      auto data = std::move(h.m_reuseData);
+      int err =
+          uv_tcp_init_ex(h.GetLoopRef().GetRaw(), h.GetRaw(), data->flags);
+      if (err < 0) {
+        h.ReportError(err);
+        return;
+      }
+      data->callback();
+    });
+  }
+}
+
 std::shared_ptr<Tcp> Tcp::Accept() {
   auto client = Create(GetLoopRef());
   if (!client) return nullptr;

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

@@ -56,6 +56,18 @@ class Tcp final : public NetworkStreamImpl<Tcp, uv_tcp_t> {
     return Create(*loop, flags);
   }
 
+  /**
+   * Reuse this handle.  This closes the handle, and after the close completes,
+   * reinitializes it (identically to Create) and calls the provided callback.
+   * Unlike Close(), it does NOT emit the closed signal, however, IsClosing()
+   * will return true until the callback is called.  This does nothing if
+   * IsClosing() is true (e.g. if Close() was called).
+   *
+   * @param flags Flags
+   * @param callback Callback
+   */
+  void Reuse(std::function<void()> callback, unsigned int flags = AF_UNSPEC);
+
   /**
    * Accept incoming connection.
    *
@@ -304,6 +316,12 @@ class Tcp final : public NetworkStreamImpl<Tcp, uv_tcp_t> {
 
  private:
   Tcp* DoAccept() override;
+
+  struct ReuseData {
+    std::function<void()> callback;
+    unsigned int flags;
+  };
+  std::unique_ptr<ReuseData> m_reuseData;
 };
 
 /**