高性能大容量SOCKET并发（四）：粘包、分包、解包
粘包
使用TCP长连接就会引入粘包的问题，粘包是指发送方发送的若干包数据到接收方接收时粘成一包，从接收缓冲区看，后一包数据的头紧接着前一包数据的尾。粘包可能由发送方造成，也可能由接收方造成。TCP为提高传输效率，发送方往往要收集到足够多的数据后才发送一包数据，造成多个数据包的粘连。如果接收进程不及时接收数据，已收到的数据就放在系统接收缓冲区，用户进程读取数据时就可能同时读到多个数据包。
粘包一般的解决办法是制定通讯协议，由协议来规定如何分包解包。
分包
在IOCPDemo例子程序中，我们分包的逻辑是先发一个长度，然后紧接着是数据包内容，这样就可以把每个包分开。
应用层数据包格式如下：
应用层数据包格式
数据包长度Len：Cardinal（4字节无符号整数） 数据包内容，长度为Len
IOCPSocket分包处理主要代码，我们收到的数据都是在TSocketHandle.ProcessIOComplete方法中处理：
procedure TSocketHandle.ProcessIOComplete(AIocpRecord: PIocpRecord; const ACount: Cardinal); begin case AIocpRecord.IocpOperate of ioNone: Exit; ioRead: //收到数据 begin FActiveTime := Now; ReceiveData(AIocpRecord.WsaBuf.buf, ACount); if FConnected then PreRecv(AIocpRecord); //投递请求 end; ioWrite: //发送数据完成，需要释放AIocpRecord的指针 begin FActiveTime := Now; FSendOverlapped.Release(AIocpRecord); end; ioStream: begin FActiveTime := Now; FSendOverlapped.Release(AIocpRecord); WriteStream; //继续发送流 end; end; end;
procedure TSocketHandle.ReceiveData(AData: PAnsiChar; const ALen: Cardinal); begin FInputBuf.Write(AData^, ALen); Process; end;
procedure TSocketHandle.Process; var AData, ALast, NewBuf: PByte; iLenOffset, iOffset, iReserveLen: Integer; function ReadLen: Integer; var wLen: Word; cLen: Cardinal; begin FInputBuf.Position := iOffset; if FLenType = ltWord then begin FInputBuf.Read(wLen, SizeOf(wLen)); //wLen := ntohs(wLen); Result := wLen; end else begin FInputBuf.Read(cLen, SizeOf(cLen)); //cLen := ntohl(cLen); Result := cLen; end; end; begin case FLenType of ltWord, ltCardinal: begin if FLenType = ltWord then iLenOffset := 2 else iLenOffset := 4; iReserveLen := 0; FPacketLen := 0; iOffset := 0; if FPacketLen <= 0 then begin if FInputBuf.Size < iLenOffset then Exit; FInputBuf.Position := 0; //移动到最前面 FPacketLen := ReadLen; iOffset := iLenOffset; iReserveLen := FInputBuf.Size - iOffset; if FPacketLen > iReserveLen then //不够一个包的长度 begin FInputBuf.Position := FInputBuf.Size; //移动到最后，以便接收后续数据 FPacketLen := 0; Exit; end; end; while (FPacketLen > 0) and (iReserveLen >= FPacketLen) do //如果数据够长，则处理 begin //多个包循环处理 AData := Pointer(Longint(FInputBuf.Memory) + iOffset); //取得当前的指针 Execute(AData, FPacketLen); iOffset := iOffset + FPacketLen; //移到下一个点 FPacketLen := 0; iReserveLen := FInputBuf.Size - iOffset; if iReserveLen > iLenOffset then //剩下的数据 begin FPacketLen := ReadLen; iOffset := iOffset + iLenOffset; iReserveLen := FInputBuf.Size - iOffset; if FPacketLen > iReserveLen then //不够一个包的长度，需要把长度回退 begin iOffset := iOffset - iLenOffset; iReserveLen := FInputBuf.Size - iOffset; FPacketLen := 0; end; end else //不够长度字节数 FPacketLen := 0; end; if iReserveLen > 0 then //把剩下的自己缓存起来 begin ALast := Pointer(Longint(FInputBuf.Memory) + iOffset); GetMem(NewBuf, iReserveLen); try CopyMemory(NewBuf, ALast, iReserveLen); FInputBuf.Clear; FInputBuf.Write(NewBuf^, iReserveLen); finally FreeMemory(NewBuf); end; end else begin FInputBuf.Clear; end; end; else begin FInputBuf.Position := 0; AData := Pointer(Longint(FInputBuf.Memory)); //取得当前的指针 Execute(AData, FInputBuf.Size); FInputBuf.Clear; end; end; end;
function TBaseSocket.DecodePacket(APacketData: PByte; const ALen: Integer): Boolean; var CommandLen: Integer; UTF8Command: UTF8String; begin if ALen > 4 then //命令长度为4字节，因而长度必须大于4 begin CopyMemory(@CommandLen, APacketData, SizeOf(Cardinal)); //获取命令长度 Inc(APacketData, SizeOf(Cardinal)); SetLength(UTF8Command, CommandLen); CopyMemory(PUTF8String(UTF8Command), APacketData, CommandLen); //读取命令 Inc(APacketData, CommandLen); FRequestData := APacketData; //数据 FRequestDataLen := ALen - SizeOf(Cardinal) - CommandLen; //数据长度 FRequest.Text := Utf8ToAnsi(UTF8Command); //把UTF8转为Ansi Result := True; end else Result := False; end;
procedure TSQLSocket.Execute(AData: PByte; const ALen: Cardinal); var sErr: string; begin inherited; FRequest.Clear; FResponse.Clear; try AddResponseHeader; if ALen = 0 then begin DoFailure(CIPackLenError); DoSendResult; Exit; end; if DecodePacket(AData, ALen) then begin FResponse.Clear; AddResponseHeader; case StrToSQLCommand(Command) of scLogin: begin DoCmdLogin; DoSendResult; end; scActive: begin DoSuccess; DoSendResult; end; scSQLOpen: begin DoCmdSQLOpen; end; scSQLExec: begin DoCmdSQLExec; DoSendResult; end; scBeginTrans: begin DoCmdBeginTrans; DoSendResult; end; scCommitTrans: begin DoCmdCommitTrans; DoSendResult; end; scRollbackTrans: begin DoCmdRollbackTrans; DoSendResult; end; else DoFailure(CINoExistCommand, 'Unknow Command'); DoSendResult; end; end else begin DoFailure(CIPackFormatError, 'Packet Must Include \r\n\r\n'); DoSendResult; end; except on E: Exception do //发生未知错误，断开连接 begin sErr := RemoteAddress + ':' + IntToStr(RemotePort) + CSComma + 'Unknow Error: ' + E.Message; WriteLogMsg(ltError, sErr); Disconnect; end; end; end;
