Indy的idTcpServer如何判断连接已断开(300分)

如何判断Indy的idTcpServer因客户端机器死机（或断电）造成的连接断开？

设置一个读写超时，超过了这个时间没有新的数据进来就是对方断开了

原码如下：
unit ServerFrmMainUnit;

interface

uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls, IdTCPServer, IdThreadMgr, IdThreadMgrDefault, IdBaseComponent,
IdComponent;

type
TCommBlock = record // the Communication Block used in both parts (Server+Client)
Command,
MyUserName, // the sender of the message
Msg, // the message itself
ReceiverName: string[100]; // name of receiver
end;

type
PClient = ^TClient;
TClient = record // Object holding data of client (see events)
DNS : String[20]; { Hostname }
Connected, { Time of connect }
LastAction : TDateTime; { Time of last transaction }
Thread : Pointer; { Pointer to thread }
end;

TServerFrmMain = class(TForm)
Server: TIdTCPServer;
CBServerActive: TCheckBox;
Protocol: TMemo;
IdThreadMgrDefault1: TIdThreadMgrDefault;

procedure CBServerActiveClick(Sender: TObject);
procedure ServerConnect(AThread: TIdPeerThread);
procedure ServerExecute(AThread: TIdPeerThread);
procedure ServerDisconnect(AThread: TIdPeerThread);
procedure FormCreate(Sender: TObject);
procedure FormClose(Sender: TObject; var Action: TCloseAction);

private

public
end;

var
ServerFrmMain : TServerFrmMain;
Clients : TThreadList; // Holds the data of all clients

implementation

uses GlobalUnit;

{$R *.DFM}

procedure TServerFrmMain.CBServerActiveClick(Sender: TObject);
begin
Server.Active := CBServerActive.Checked;
end;

procedure TServerFrmMain.ServerConnect(AThread: TIdPeerThread);
var
NewClient: PClient;

begin
GetMem(NewClient, SizeOf(TClient));

NewClient.DNS := AThread.Connection.LocalName;
NewClient.Connected := Now;
NewClient.LastAction := NewClient.Connected;
NewClient.Thread :=AThread;

AThread.Data:=TObject(NewClient);

try
Clients.LockList.Add(NewClient);
finally
Clients.UnlockList;
end;

Protocol.Lines.Add(TimeToStr(Time)+' Connection from "'+NewClient.DNS+'"');
end;

procedure TServerFrmMain.ServerExecute(AThread: TIdPeerThread);
var
ActClient, RecClient: PClient;
CommBlock, NewCommBlock: TCommBlock;
RecThread: TIdPeerThread;
i: Integer;

begin
if not AThread.Terminated and AThread.Connection.Connected then
begin
AThread.Connection.ReadBuffer (CommBlock, SizeOf (CommBlock));
ActClient := PClient(AThread.Data);
ActClient.LastAction := Now; // update the time of last action

if (CommBlock.Command = 'MESSAGE') or (CommBlock.Command = 'DIALOG') then
begin // 'MESSAGE': A message was send - forward or broadcast it
// 'DIALOG': A dialog-window shall popup on the recipient's screen
// it's the same code for both commands...

if CommBlock.ReceiverName = '' then
begin // no recipient given - broadcast
Protocol.Lines.Add (TimeToStr(Time)+' Broadcasting '+CommBlock.Command+': "'+CommBlock.Msg+'"');
NewCommBlock := CommBlock; // nothing to change ;-))

with Clients.LockList do
try
for i := 0 to Count-1 do // iterate through client-list
begin
RecClient := Items; // get client-object
RecThread := RecClient.Thread; // get client-thread out of it
RecThread.Connection.WriteBuffer(NewCommBlock, SizeOf(NewCommBlock), True); // send the stuff
end;
finally
Clients.UnlockList;
end;
end
else
begin // receiver given - search him and send it to him
NewCommBlock := CommBlock; // again: nothing to change ;-))
Protocol.Lines.Add(TimeToStr(Time)+' Sending '+CommBlock.Command+' to "'+CommBlock.ReceiverName+'": "'+CommBlock.Msg+'"');
with Clients.LockList do
try
for i := 0 to Count-1 do
begin
RecClient:=Items;
if RecClient.DNS=CommBlock.ReceiverName then // we don't have a login function so we have to use the DNS (Hostname)
begin
RecThread:=RecClient.Thread;
RecThread.Connection.WriteBuffer(NewCommBlock, SizeOf(NewCommBlock), True);
end;
end;
finally
Clients.UnlockList;
end;
end;
end
else
begin // unknown command given
Protocol.Lines.Add (TimeToStr(Time)+' Unknown command from "'+CommBlock.MyUserName+'": '+CommBlock.Command);
NewCommBlock.Command := 'DIALOG'; // the message should popup on the client's screen
NewCommBlock.MyUserName := '[Server]'; // the server's username
NewCommBlock.Msg := 'I don''t understand your command: "'+CommBlock.Command+'"'; // the message to show
NewCommBlock.ReceiverName := '[return-to-sender]'; // unnecessary

AThread.Connection.WriteBuffer (NewCommBlock, SizeOf (NewCommBlock), true); // and there it goes...
end;
end;
end;

procedure TServerFrmMain.ServerDisconnect(AThread: TIdPeerThread);
var
ActClient: PClient;

begin
ActClient := PClient(AThread.Data);
Protocol.Lines.Add (TimeToStr(Time)+' Disconnect from "'+ActClient^.DNS+'"');
try
Clients.LockList.Remove(ActClient);
finally
Clients.UnlockList;
end;
FreeMem(ActClient);
AThread.Data := nil;
end;

procedure TServerFrmMain.FormCreate(Sender: TObject);
begin
Clients := TThreadList.Create;
end;

procedure TServerFrmMain.FormClose(Sender: TObject; var Action: TCloseAction);
begin
Server.Active := False;
Clients.Free;
end;

end.

AThread.Connection.Connected 不行吗？

如何判断Indy的idTcpServer因客户端机器死机（或断电）造成的连接断开，
AThread.Connection.Connected 好像不行吧

对，确实不能判断他是否断开，所以服务器必须一直在等待新的数据到来或者是在写数据
我认为要判断Client是否断开，写操作失败不能说明问题，只要读操作长时间没有收到
数据才能说明对方断开了

if Athread=nil then exit;
if Athread.Terminated then exit;
if Not AThread.Connection.Connected then exit;
就可以解决了

To StevenPeng:
可是因为idTcpServer是阻塞的，所以他会停在Read上，这时客户端机器死机，服务器
还是停在Read上，你的代码并没有解决问题，让他从Read中跳出来。

To 张无忌
因为idTcpServer是阻塞的， 如果设一个timeout，那么客户端没有断开时，如果很长
时间没有发送数据，idTcpServer就会认为它断开了。

to qince:
如果不这样，你根本没有办法判断是否断开，除非你要Client在空闲里发送
小数据包，证明自己还在线，这样看，还是用我的办法，如果长时间没收到
数据就断开。。。

To 张无忌
（如果不这样，你根本没有办法判断是否断开，除非你要Client在空闲里发送
小数据包，证明自己还在线，这样看，还是用我的办法，如果长时间没收到
数据就断开。。。）
可是我们的客户端已经写完代码了，要改很困难。我想Indy不会不提供判断客户端
非法断开的方法吧？

这个控件当然不会提供，因为这涉及到协议，一般要自己写的。。。，

To 张无忌
可是如果用API写阻塞方式，如果客户端死机，那么服务端会从READ中返回，且
READ返回0字节。这样就能判断客户端非法断开。

不啊，如果连接方死了，不一定发FIN数据包给你的，TCP不保证及时的断开通知，要自己写

To 张无忌
可以提供用Indy判断对方非法断开的编码思路吗？

我说过了的，就是读数据超时

还有一种办法，比如在聊天室里，因为你不停的把数据广播般发出去，这个时候就不用考虑异常
推出的问题，如果发送失败，可以考虑关掉套接字（只要不是有人刷屏），

To 张无忌
谢谢，还有其他方法吗？因为设置一个读写超时，超过了这个时间没有新的数据进来
服务端就会认为客户端非法断开。

基本上没其他好的办法了...

可不可以每隔几秒钟ping一下客户端，如果连续几次ping不通，就认为客户端死机，然
后处理断开连接?