How do I send filename from server to client in MFC socket programming

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I'm just trying to read filename i have in folder and send the name to client so that client will create file with that name. Fyi... I'm sending the filename through command header. The code I written is sending the name from server but receiver is not getting it. here's my command header:

typedef enum {
    CREATE_FILE     =   0,
    SEND_FILE       =   10,
    FILE_SIZE       =   20,
}CommandList;

typedef struct {
    CommandList command;
    CString iDataBuffer;
} COMMAND_HEADER;

Server Code:
COMMAND_HEADER command_header; 
command_header.command = CREATE_FILE;
command_header.iDataBuffer = findfile.cFileName;
int nfRet = SockConnection.Send((char*)&command_header,
sizeof(command_header));

nfRet = SockConnection.Send(command_header.iDataBuffer,
sizeof(command_header.iDataBuffer));

Client code:
CString fname[50];
int nRet = SockConnection.Receive((char*)&hCommand_header, sizeof(hCommand_header));
nRet = SockConnection.Receive(fname, 50);<pre>

what am I doing wrong?

What I have tried:

here, fname receives like <bad ptr>garbage values. Please let me know if this not clear and I'll strive to make this right.

Posted 30-Jan-19 20:40pm

rmds

Updated 30-Jan-19 22:10pm

v4

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CPallini · Accepted Answer · 2019-01-30T22:11:00

Solution 1

Quote:
int nfRet = SockConnection.Send((char*)&command_header,
sizeof(command_header));

nfRet = SockConnection.Send(command_header.iDataBuffer,
sizeof(command_header.iDataBuffer));

The above calls don't make sense.
On my system

sizeof(command_header)=8
sizeof(command_header.iDataBuffer)=4

independent on actual iDataBuffer string length.
You should write something similar to

C++

int nfRet = SockConnection.Send((char*)&command_header.command,
sizeof(command_header.command));// send the command
size_t iDataLen = command_header.iDataBuffer.GetLength() * sizeof(TCHAR);
nfRet = SockConnection.Send((char*)command_header.iDataBuffer.GetBuffer(),
iDataLen);
command_header.iDataBuffer.ReleaseBuffer();

Posted 30-Jan-19 22:11pm

CPallini

Comments

rmds 31-Jan-19 4:42am

Thank you, it says a lot! I tried above however, still receiving client not getting the filename. Here's my client end code:

COMMAND_HEADER hCommand_header;
CString fname[50];
int nRet = SockConnection.Receive((char*)&hCommand_header, sizeof(hCommand_header));
switch(hCommand_header.command) {
case CREATE_FILE: {
nRet = SockConnection.Receive((char*)&hCommand_header.iDataBuffer, 50); // instead I
// also tried this:
nRet = SockConnection.Receive(fname, 50);
}
break;
Thank you!

rmds 31-Jan-19 5:04am

OK...instead this code reads the filename but along with the garbage value:
int nRet = SockConnection.Receive((char*)&hCommand_header.command,
sizeof(hCommand_header.command));

switch(hCommand_header.command) {
case CREATE_FILE: {
nRet = SockConnection.Receive((char*)hCommand_header.iDataBuffer.GetBuffer(), 50);
}
break;

how to get rid of the garbage and unpack the filename to CString?

rmds 31-Jan-19 5:14am

I got it. It worked! Thank you very much!!!

CPallini 31-Jan-19 5:53am

You are welcome. I suppose you have sent the lenght of the string, before its actual content.

rmds 31-Jan-19 7:44am

I hate to trouble but been checking for quite a while now... A txtfile with the name is created, however the above code crashes with error dialog"Heap Corruption Detected: after Normal block. "CRT detected that the application wrote to memory end of heap buffer". It crashes when I press F10 after "DestFile.Open" in following code:

switch(hCommand_header.command) {
case CREATE_FILE: {
nRet = SockConnection.Receive((char*)hCommand_header.iDataBuffer.GetBuffer(),50);
(hCommand_header.iDataBuffer.GetBuffer())[nRet] = '\0';
Destfile.Open(hCommand_header.iDataBuffer, CFile::modeCreate | CFile::modeWrite);
}
hCommand_header.iDataBuffer.ReleaseBuffer();
break;

CPallini 31-Jan-19 8:27am

Try
nRet = SockConnection.Receive((char*)hCommand_header.iDataBuffer.GetBuffer(50),50*sizeof(TCHAR));
hCommand_header.iDataBuffer.ReleaseBuffer(nRet/sizeof(TCHAR));
Destfile.Open(hCommand_header.iDataBuffer, CFile::modeCreate | CFile::modeWrite);

and remove your ReleaseBuffer() call.

rmds 1-Feb-19 5:33am

Could you please lemme know how you comeup with the calculation of GetBuffer() and ReleaseBuffer()? This is pure mastermind!!! and it worked for CREATE_FILE Command. But, wen I'm changing command to SEND_FILE, hCommand_header.iDataBuffer still has garbage values. thank you very much

CPallini 1-Feb-19 5:43am

I guess you'd better use plain memory buffers instead of CStrings for socket communication.

CPallini 1-Feb-19 5:42am

both GetBuffer and ReleaseBuffer take the number of characters while the socket functions use bytes. The number of bytes is:

bytes = sizeof(TCHAR)*characters

The number of characters is

characters = bytes /sizeof(TCHAR)

Where sizeof(TCHAR) is 1 in ANSI builds, and 2 in UNICODE builds.

rmds 1-Feb-19 5:47am

Here's the snippet:

SERVER SIDE:

command_header.command = SEND_FILE;
command_header.iDataBuffer = findfile.cFileName;
int nfRet = SockConnection.Send((char*)&command_header.command,
sizeof(command_header.command));
size_t iDataLen = command_header.iDataBuffer.GetLength() * sizeof(TCHAR);
nfRet = SockConnection.Send((char*)command_header.iDataBuffer.GetBuffer(),iDataLen);
switch(command_header.command) {
case SEND_FILE: {
CFile Sourcefile;
Sourcefile.Open(Filepath, CFile::modeRead);
ULONGLONG dwLength = Sourcefile.GetLength();
command_header.DataBuffer = new char[(int)dwLength + 1];
UINT nActual = Sourcefile.Read(command_header.DataBuffer,dwLength);
command_header.DataBuffer[nActual] = 0;
nfRet = SockConnection.Send(command_header.DataBuffer, nActual);

CLIENT SIDE:
COMMAND_HEADER hCommand_header;
CFile Destfile;
char nBuf[1000];
int nRet = SockConnection.Receive((char*)&hCommand_header.command,
sizeof(hCommand_header.command));
nRet = SockConnection.Receive((char*)hCommand_header.iDataBuffer.GetBuffer(50),
50*sizeof(TCHAR));
hCommand_header.iDataBuffer.ReleaseBuffer(nRet/sizeof(TCHAR));

here: hCommand_header.iDataBuffer still has junk that was not the case in CREATE_FILE command.