一个文件传输代码中的问题

[arden1019]

下面是一段从server端向client端发送文件的代码：
UINT CFileTransferServerView::ThreadedSendFileToRemoteRecipient(LPVOID pVoid)
{

CFileTransferServerView* pThis = (CFileTransferServerView*)pVoid;
pThis->PostMessage( UWM_FILESENDEVENT, FSE_THREADSTART, 0L );

AfxSocketInit(NULL); // make certain this is done somewhere in each thread (usually in InitInstance for main thread)
CSocket sockSrvr;
sockSrvr.Create(PRE_AGREED_PORT); // Creates our server socket
sockSrvr.Listen(); // Start listening for the client at PORT
CSocket sockConnection;
sockSrvr.Accept(sockConnection); // Use another CSocket to accept the connection

pThis->PostMessage( UWM_FILESENDEVENT, FSE_STATUSCONNECTED, 0L );

// local variables used in file transfer (declared here to avoid "goto skips definition"-style compiler errors)

int fileLength, cbLeftToSend; // used to monitor the progress of a sending operation
int simulate; // used to simulate mismatch events (if designated by user)

BYTE* sendData = NULL; // pointer to buffer for sending data (memory is allocated after sending file size)

int pbInterval = 0; int curPB = 0; // progress bar variables


CFile sourceFile;
CFileException fe;
BOOL bFileIsOpen = FALSE;

if( !( bFileIsOpen = sourceFile.Open( pThis->m_strFileName, CFile::modeRead | CFile::typeBinary, &fe ) ) )
{
TCHAR strCause[256];
fe.GetErrorMessage( strCause, 255 );
TRACE( "SendFileToRemoteRecipient encountered an error while opening the local file\n"
"\tFile name = %s\n\tCause = %s\n\tm_cause = %d\n\tm_IOsError = %d\n",
fe.m_strFileName, strCause, fe.m_cause, fe.m_lOsError );

/* you should handle the error here */

goto PreReturnCleanup;
}



// first send length of file

fileLength = sourceFile.GetLength();
fileLength = htonl( fileLength );

cbLeftToSend = sizeof( fileLength );

// Inject mismatch events (if selected by user)
// Seed the random-number generator with current time
srand( (unsigned)time( NULL ) );

simulate = 1 + rand() % 2; // either 1 or 2
simulate = ( pThis->m_bSimulateEvents ) ? simulate : 0; // zero if user de-selected event simulation

do
{
int cbBytesSent;
BYTE* bp = (BYTE*)(&fileLength) + sizeof(fileLength) - cbLeftToSend;
cbBytesSent = sockConnection.Send( bp, cbLeftToSend - simulate );
simulate = 0;

// test for errors and get out if they occurred
if ( cbBytesSent == SOCKET_ERROR )
{
int iErr = ::GetLastError();
TRACE( "SendFileToRemoteRecipient returned a socket error while sending file length\n"
"\tNumber of Bytes sent = %d\n"
"\tGetLastError = %d\n", cbBytesSent, iErr );

/* you should handle the error here */

goto PreReturnCleanup;
}

// data was successfully sent, so account for it with already-sent data
cbLeftToSend -= cbBytesSent;
}
while ( cbLeftToSend>0 );


// now send the file's data

sendData = new BYTE[SEND_BUFFER_SIZE];

cbLeftToSend = sourceFile.GetLength();


// set up progress bar

fileLength = cbLeftToSend;
pbInterval = fileLength>>7; // divide by 128
curPB = 0;

pThis->m_ctlProgressSend.PostMessage( PBM_SETPOS, (WPARAM) curPB, 0L );

do
{
// read next chunk of SEND_BUFFER_SIZE bytes from file

int sendThisTime, doneSoFar, buffOffset;

sendThisTime = sourceFile.Read( sendData, SEND_BUFFER_SIZE );
buffOffset = 0;

// simulate mismatch events

simulate = rand();
simulate = ( simulate>RAND_MAX/10 ) ? 0 : 2560*simulate/RAND_MAX ; // up to 256 but only inject mismatches 10% of the time
simulate = ( pThis->m_bSimulateEvents ) ? simulate : 0 ; // zero if user de-selected event simulation

do
{
doneSoFar = sockConnection.Send( sendData + buffOffset, sendThisTime - simulate );
simulate = 0;

// test for errors and get out if they occurred
if ( doneSoFar == SOCKET_ERROR )
{
int iErr = ::GetLastError();
TRACE( "SendFileToRemoteRecipient returned a socket error while sending chunked file data\n"
"\tNumber of Bytes sent = %d\n"
"\tGetLastError = %d\n", doneSoFar, iErr );

/* you should handle the error here */

goto PreReturnCleanup;
}

// data was successfully sent, so account for it with already-sent data
// but first, advise main thread of a send mismatch if everything was not sent in one shot

if ( doneSoFar != sendThisTime )
{
pThis->m_iNumMismatches++;
pThis->PostMessage( UWM_FILESENDEVENT, FSE_UPDATECONTROLS, 0L );
}

buffOffset += doneSoFar;
sendThisTime -= doneSoFar;
cbLeftToSend -= doneSoFar;
}
while ( sendThisTime > 0 );

// update progress bar

if ( pbInterval*curPB < (fileLength-cbLeftToSend) )
{
curPB++;
pThis->m_ctlProgressSend.PostMessage( PBM_SETPOS, (WPARAM) curPB, 0L );
}

}
while ( cbLeftToSend > 0 );


PreReturnCleanup: // labelled goto destination

// free allocated memory
// if we got here from a goto that skipped allocation, delete of NULL pointer
// is permissible under C++ standard and is harmless
delete[] sendData;

if ( bFileIsOpen )
sourceFile.Close(); // only close file if it's open (open might have failed above)

sockConnection.Close();

// advise main thread that we're completed
pThis->PostMessage( UWM_FILESENDEVENT, FSE_THREADCOMPLETE, 0L );

return 0;

}


1：其中的simulate实现了什么功能？
2：在第一个do while循环中完成了什么功能？BYTE* bp = (BYTE*)(&fileLength) + sizeof(fileLength) - cbLeftToSend; 是什么意思？

我感觉第一个do while 应该是完成文件大小的传递，是不是呢？

[yzcurry]

up

[cloudgamer]

这样很难看阿

[vivimimi]

太多了。描述一下

[cenchure]

didi ， 你要先用文字描述好你的要实现这个功能的步步骤 ， 按照步骤来分解成子函数，递归进行。 这样你自己 就 可以很清楚的判断了 。

[templarzq]

mark

[arden1019]

仔细看看，又仔细想想，基本上看明白了：）