Finish std::shared_ptr -> Ref migration

src/connection.cpp

@@ -38,10 +38,14 @@ static thread_local std::vector<struct iovec> g_iovec_buffer{IOV_MAX};
 
 Connection::Connection(struct sockaddr_storage addr, int fd, int64_t id,
                        size_t epoll_index, ConnectionHandler *handler,
-                       Server &server)
+                       WeakRef<Server> server)
     : fd_(fd), id_(id), epoll_index_(epoll_index), addr_(addr), arena_(),
-      handler_(handler), server_(server.weak_from_this()) {
-  server.active_connections_.fetch_add(1, std::memory_order_relaxed);
+      handler_(handler), server_(std::move(server)) {
+  auto server_ref = server_.lock();
+  // This should only be called from a member of Server itself, so I should
+  // hope it's alive.
+  assert(server_ref);
+  server_ref->active_connections_.fetch_add(1, std::memory_order_relaxed);
 
   // Increment connection metrics using thread-local instances
   connections_total.inc();
@@ -55,6 +59,7 @@ Connection::~Connection() {
   if (handler_) {
     handler_->on_connection_closed(*this);
   }
+  // Server may legitimately be gone now
   if (auto server_ptr = server_.lock()) {
     server_ptr->active_connections_.fetch_sub(1, std::memory_order_relaxed);
   }