Thread: Write to a file from a socket?

i am having a hard to trying to write a .exe such as calc.exe from a recv Buffer to the file thats created with CreateFile , here is my loop

Code:

while(recv(sock,Buffer,sizeof(Buffer),0) > 0)
{
			
   printf("%s\n","writing contents to file");
   WriteFile(f,Buffer,sizeof(Buffer),&written,0);
   Sleep(50);
}

does anyonr know the correct way?

Code:

 int amount;
			while(1)
			{
				amount = recv(sock,Buffer,sizeof(Buffer),0);
			
				if(amount > 0)
				{
					printf("%s %i\n","Bytes Recieved", amount);
			        WriteFile(f,Buffer,amount,&written,0);
				}
				else
				{
					break;
				}
			}

still cant get it working

I suggest you check all the returns if things go wrong.

This will happen in every app you write, so learning to diagnose these types of issues is vital.



Tell us what this returns (not complied, off the top of my head...)

Code:

int iRet=0,iErr=0;


iRet=WriteFile(f,Buffer,amount,&written,0);
//WriteFile returns 0 for success
if(iRet)
{
     //error occured in WriteFile()
     iErr=GetLastError();
     printf("WriteFile failed with %d and GLE returned %d.",iRet,iErr);
}
//but we should also check if the right amount was writen to file. 
else if(amount!=written)
{
    //WriteFile did not write the correct amount to the file
    iErr=GetLastError();
     printf("WriteFile wrote wrong amount %d of %d [GLE returned %d].",amount,written,iErr);
}
//else success

EDIT:
I also wonder what will happen if amount == sizeof(Buffer) as you will not have a null terminator.

Probably nothing in a complier (and 99.99% of the time in release) but I would be inclined to use (sizeof(Buffer)-1) in recv()

Originally Posted by novacain

I also wonder what will happen if amount == sizeof(Buffer) as you will not have a null terminator.

Probably nothing in a complier (and 99.99% of the time in release) but I would be inclined to use (sizeof(Buffer)-1) in recv()

Why do you need a nul-terminator in the binary buffer? It is not a string and it is not passed to any function expecting string. So why do you need it?

Originally Posted by vart

Why do you need a nul-terminator in the binary buffer? It is not a string and it is not passed to any function expecting string. So why do you need it?

You are right but...

I don't see a declaration, so we don't know it is a byte array.

recv() lists the param as a char* so I assumed an inexperienced (with sockets) coder would use a char array.

As I said '99.99%' and 'inclined'.

I see no harm in being overly careful or teaching people to write robust code (but I write mission critical assest protection systems so I tend to be overly cautious).

Originally Posted by Anddos

i am having a hard to trying to write a .exe such as calc.exe from a recv Buffer to the file thats created with CreateFile , here is my loop

Code:

while(recv(sock,Buffer,sizeof(Buffer),0) > 0)
{
			
   printf("%s\n","writing contents to file");
   WriteFile(f,Buffer,sizeof(Buffer),&written,0);
   Sleep(50);
}

does anyonr know the correct way?

You really should post the code for both the client and server in order for anyone to provide a reasonable solution. Issues may be found on one or both sides.

But anyway, I wrote a very basic file transfer util and my approach was to first transfer the file information (which includes the file size) to the destination host. I used the following structure:

Code:

typedef struct {
    CHAR  szName[MAX_PATH + 1];
    ULARGE_INTEGER ulFileSize;
  
} REQUIREDFILEINFO;

My file data receive is as follows:

Code:

REQUIREDFILEINFO  fReqFileInfo;

while(fReqFileInfo.ulFileSize.QuadPart > 0 && ((iLen = recv(iClient, szBuffer, 4096, 0)) > 0))
{
        if(!WriteFile(handle, szBuffer, iLen, &dwWrite, NULL)) break;
        fReqFileInfo.ulFileSize.QuadPart -= iLen;
}

After the file information is transferred to the destination, the file data is then transferred in 4K chunks.

As Alex31 would say, this issue has been discussed (and solved) many times on the Win32 newsgroups.