Delphi XE2 Indy10 udp客户端-服务器交换使用SendBuffer-ReceiveBuffer

Question

我使用Delphi XE2和Indy10 UDP协议。如果我使用ReceiveBuffer方法，我无法在客户端接收服务器回声。我得到了"套接字错误# 10040"，虽然我发回非常小的回声从服务器到客户机的消息。控制台应用程序来说明我的问题如下。提前谢谢。

program Project1;
{$APPTYPE CONSOLE}
{$R *.res}
uses
  System.SysUtils, IdGlobal, IdBaseComponent, IdComponent, IdSocketHandle,
  IdUDPClient, IdUDPServer, IdUDPBase, IdStack;
type
  TUDP_Serv = class(TIdUDPServer)
    procedure udpSvUDPRead(AThread: TIdUDPListenerThread;
      AData: TIdBytes; ABinding: TIdSocketHandle);
  end;
var
  udpServer: TUDP_Serv;
  udpCl: TIdUDPClient;
  bSnd, bRcv: TBytes;
  s: string;
  k: integer;
//==============================================================================
procedure TUDP_Serv.udpSvUDPRead(AThread: TIdUDPListenerThread; AData: TIdBytes;
  ABinding: TIdSocketHandle);
begin
writeln(' Server read: ' + ToHex(AData, length(AData)));
with ABinding do SendTo(PeerIP, PeerPort, AData);
end;
//==============================================================================
begin
try
  udpServer := TUDP_Serv.Create;
  with udpServer do begin
    OnUDPRead := udpSvUDPRead; DefaultPort := 20001; BufferSize := 2048;
    ThreadedEvent := true; Active := True;
    if Active then writeln('Server started on port: ' + IntToStr(DefaultPort));
  end;
  udpCl := TIdUDPClient.Create;
  with udpCl do begin
    BufferSize := 2048; Host := '127.0.0.1'; Port := 20001;
  end;
  SetLength(bSnd, 5); bSnd[0] := $31; bSnd[1] := $0;
  bSnd[2] := $33; bSnd[3] := $0; bSnd[4] := $0;
  repeat
    writeln(' Client send: ' + ToHex(bSnd, length(bSnd)));
    with udpCl do SendBuffer(Host, Port, bSnd); sleep(100);
    try
      k := udpCl.ReceiveBuffer(bRcv, 10);
      if k > 0 then writeln(' Client read: ' + ToHex(bRcv, length(bRcv)));
    except
      on E: exception do begin
        writeln(Format(' Client read err: %s',[E.Message]));
      end;
    end;
    readln(s);
  until s <> '';
except
  on E: Exception do begin
    Writeln(E.ClassName, ': ', E.Message); readln(s);
  end;
end;
end.

屏幕输出:

Server started on prot: 20001
 Client send: 3100330000
 Server read: 3100330000
Client read err: Socket Error # 10040
Message too long.

Answer 1

10040是WSAEMSGSIZE，这意味着您尝试接收到的缓冲区小于接收到的消息的实际大小。

在调用ReceiveBuffer()之前，您没有为bRcv分配任何内存，因此您试图接收到0字节的缓冲区，因此出现错误。您需要将bRcv预分配到至少与消息相同的大小，如果不是更大的话。

ReceiveBuffer()不为每个接收到的消息分配一个新的TBytes。您必须事先自己分配缓冲区，然后ReceiveBuffer()将仅仅填充它，返回实际接收到的字节数。