Thread: File Writing Problem

So I'm writing a file transfer routine for two networked machines. I have a working version that has one machine read in the entire file into a buffer, and then transfer chunks over the network. However, I'd like to read in chunks from the file and send them as I go in case the file is very large. With that version, the file is transferred, it has the correct size, but no matter what file type it is, it will not open. For example, a .jpg throws an error saying "DNL not supported" or a text file has improper encoding.

The code for the two version is very similar and I'm unable to figure out what the problem is. I believe the sendFile() function is where the problem is seeing as that is the function that differs in the two versions.

Any help would be appreciated!

Here is the working version that loads the entire file into memory:

Code:

void receiveFile(int sock, char* filename)
{
	FILE * pFile;
	pFile = fopen(filename, "wb");

	message msg;
	void* buffer = (void*) &msg;
	int rBytes, rv;
	int pause;
	
	int finished = 0;
	int bytesWritten = 0;
	
	while(!finished)
	{
		//ensure that we receive a complete msg object from the other end
		for(rBytes = 0; rBytes < sizeof(msg); rBytes += rv)
		{
			if((rv = recv(sock, buffer+rBytes, sizeof(msg)-rBytes, 0)) < 0)
				dieWithError("recv() failed");
		}
		
		//convert size from network to host byte order
		msg.size = ntohl(msg.size);
		
		//write the data we just received to the file
		if(msg.size - bytesWritten < sizeof(msg.data))
		{
			fwrite(msg.data,1,msg.size - bytesWritten,pFile);
			finished = 1;
		}
		else
		{
			fwrite(msg.data, 1, sizeof(msg.data), pFile);
			bytesWritten += sizeof(msg.data);
		} 
	}
	//close file
	fclose (pFile);
}

void sendFile(int sock, char* filename)
{
	FILE* pFile;
	long fileSize;
	char* buffer;
	size_t result;
	
	int copied;

	pFile = fopen(filename,"rb");
	if(pFile==NULL)
		printf("error with fopen()");
		
	// obtain file size:
	fseek(pFile, 0, SEEK_END);
	fileSize = ftell(pFile);
	fseek(pFile, 0, SEEK_SET);

	// allocate memory to contain the whole file:
	buffer = (char*)malloc(sizeof(char) * fileSize);
	if(buffer == NULL)
		printf("error with malloc()");

	// copy the file into the buffer:
	result = fread(buffer, 1, fileSize,pFile);
	if(result != fileSize)
		printf("error with fread()");

	//the whole file is now loaded in the memory buffer.
	
	//send file to other client
	message msg;
	
	copied = 0;
	while(copied < fileSize)
	{
		memset(&msg, 0, sizeof(msg));
		if(fileSize - copied < sizeof(msg.data))
		{
			memcpy(msg.data, buffer + copied, fileSize - copied);
			copied += fileSize - copied;
		}
		else
		{
			memcpy(msg.data, buffer + copied, sizeof(msg.data));
			copied += sizeof(msg.data);
		} 
		msg.size = htonl(fileSize);
		send(sock, &msg, sizeof(msg), 0);
	}

	//close file
	fclose(pFile);
	free(buffer);
}

Here is the one that doesn't work. It uses the same corresponding receiveFile() function.

Code:

void sendFile(int sock, char* filename)
{
	FILE* pFile;
	long fileSize;
	char* buffer;
	size_t readIn;
	
	int copied;

	pFile = fopen(filename,"rb");
	if(pFile==NULL)
		printf("error with fopen()");
		
	// obtain file size:
	fseek(pFile, 0, SEEK_END);
	fileSize = ftell(pFile);
	fseek(pFile, 0, SEEK_SET);
	
	//send file to other client
	message msg;
	copied = 0;
	
	while(copied < fileSize)
	{
		//allocate a buffer of appropriate size
		if(fileSize - copied < sizeof(msg.data))
			buffer = (char*)malloc((fileSize - copied) * sizeof(char));
		else
			buffer = (char*)malloc(sizeof(msg.data) * sizeof(char));
		
		//read in some data from the file
		readIn = fread(buffer, 1, sizeof(buffer), pFile);
		if(readIn != sizeof(buffer))
			printf("error with fread()");
		
		//transfer the data into our message struct
		memset(&msg, 0, sizeof(msg));
		memcpy(msg.data, buffer, sizeof(buffer));
		copied += sizeof(buffer);

		msg.size = htonl(fileSize);
		send(sock, &msg, sizeof(msg), 0);
		free(buffer);
	}

	//close file
	fclose(pFile);
}