sockets - TServerSocket : How check if a specific client on ListView still is connected before send message?

Question

我有一个 Timer并希望向 ListView 的每个客户端发送一条消息例如，确定 ping 时间。然后我有以下代码:

procedure TMainForm.Timer1Timer(Sender: TObject);
var
  i: Integer;
begin
  try
    for i := 0 to ListView1.Items.count - 1 do
    begin
      ListView1.Items.Item[i].SubItems.Objects[2] := TObject(GetTickCount);
      ServerSocket1.Socket.Connections[i].SendText('ping' + #13#10);
    end;
  except
    exit;
  end;
end;

在发送之前，可能更适合检查客户端是否真的连接或类似的。这个怎么做？提前致谢。

Answer 1

无需检查连接。如果客户端实际断开连接，它不会在服务器的Connections[] 中。当您的 OnTimer 时不再列出处理程序被触发。你应该有一个 OnClientDisconnect分配给 TServerSocket 的处理程序从 TListView 中删除客户端.

如果由于某种原因，客户端仍在 Connections[]列表(即，因为底层连接已丢失但 TServerSocket 尚未检测到它)，然后套接字将简单地缓存所有传出数据，直到其出站缓冲区填满，然后它将开始返回 WSAWOULDBLOCK每次发送的错误。最终，操作系统将超时死连接和TServerSocket将从 Connections[] 中删除它列表，触发 OnClientDisconnect事件。

至少，在您显示的代码中，您应该将发送循环更新为 Close()任何实际发送失败的套接字，从而触发 OnClientDisconnect从 TListView 中删除该客户端的事件，例如:

procedure TMainForm.ServerSocket1ClientConnect(Sender: TObject; Socket: TCustomWinSocket);
var
  Item: TListItem;
begin
  Item := ListView1.Items.Add;
  Item.Data := Socket;
  ...
end;

procedure TMainForm.ServerSocket1ClientDisconnect(Sender: TObject; Socket: TCustomWinSocket);
var
  Item: TListItem;
begin
  Item := ListView1.FindData(0, Socket, True, False);
  if Item <> nil then
    Item.Delete;
end;

procedure TMainForm.Timer1Timer(Sender: TObject);
const
  s: AnsiString = 'ping' + #13#10;
var
  Item: TListItem;
  Socket: TCustomWinSocket;
  p: PAnsiChar;
  i, len, sent: Integer;
begin
  for i := 0 to ListView1.Items.Count - 1 do
  begin
    Item := ListView1.Items[i];
    Item.SubItems.Objects[2] := TObject(GetTickCount);
    Socket := TCustomWinSocket(Item.Data);
    try
      // SendText() does not handle partial sends, or Unicode strings...
      //Socket.SendText('ping' + #13#10);
      p := PAnsiChar(s);
      len := Length(s);
      repeat
        sent := Socket.SendBuf(p^, len);
        if sent = -1 then
        being
          if WSAGetLastError() <> WSAEWOULDBLOCK then
            Break;
          // TODO: stop trying after several attempts fail...
          Continue;
        end;
        Inc(p, sent);
        Dec(len, sent);
      until len = 0;
      if len = 0 then
        Continue;
    except
    end;
    Socket.Close;
  end;
end;