Fix building ExportedConnection on Windows

[SeverinLeonhardt]

The <unistd.h> header isn't available on Windows. The dup function is deprecated¹ and apparently also not the correct function here.

On Windows uv_fileno currently returns a SOCKET² cast into uv_os_fd_t³. Contrary to many other handles this handle type can't be duplicated using DuplicateHandle⁴. WSADuplicateSocket has to be used instead. As documented an actual SOCKET has to be constructed from WSAPROTOCOL_INFOW. The parameters are taken from the struct, except for g and dwFlags which were taken from libuv's implementation⁵.

Error handling was omitted like with uv_fileno and dup already.

Also changed the type of fd to what uv_tcp_open expects which is SOCKET instead of int on Windows.

Footnotes

1. https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/posix-dup-dup2 ↩

2. https://github.com/libuv/libuv/blob/2f1614b1286f53b3b2ab96a15a525cb25462ba9a/include/uv/win.h#L456 ↩

3. https://github.com/libuv/libuv/blob/2f1614b1286f53b3b2ab96a15a525cb25462ba9a/src/win/core.c#L689 ↩

4. https://learn.microsoft.com/en-us/windows/win32/api/handleapi/nf-handleapi-duplicatehandle#remarks ↩

5. https://github.com/libuv/libuv/blob/2f1614b1286f53b3b2ab96a15a525cb25462ba9a/src/win/tcp.c#L1281-L1282 ↩

[SeverinLeonhardt]

To test whether these changes work I've applied the following patch:

diff --git a/src/connection_pool.cpp b/src/connection_pool.cpp
index 21464b18..891226ec 100644
--- a/src/connection_pool.cpp
+++ b/src/connection_pool.cpp
@@ -95,11 +95,7 @@ ConnectionPool::ConnectionPool(const Connection::Vec& connections, ConnectionPoo
        ++it) {
     const Connection::Ptr& connection(*it);
     if (!connection->is_closing()) {
-      if (connections_by_shard_[connection->shard_id()].size() < num_connections_per_shard_) {
-        add_connection(PooledConnection::Ptr(new PooledConnection(this, connection)));
-      } else {
         host_->add_unpooled_connection(std::move(connection));
-      }
     }
   }

This lead to ExportConnection's constructor and import_connection method being called.
The test application then successfully ran various CQL queries against a single-node Scylla cluster.

[Gor027]

LGTM.