QCryptographicHash an entire file

[pyramation]

Hello all!

I am successfully hashing an entire file, however, my method seems to produce different results for different block sizes. Let me explain...

My fear is that I don't want to use a Qt data structure to store an entire file to memory, since I want to hash arbitrarily large files. Hence, I am chunking the file into pieces of 'blocksize', and then using addData() to add the data to the hash.

The problem is that for different values of 'blocksize', I am getting a different hash. Any ideas?

FILE * fd = fopen(fileName.toAscii().data(), "rb");
		if (!fd) return;
 
 
		fseek(fd, 0, SEEK_END);
		long fSize = ftell(fd);
		fseek(fd, 0, SEEK_SET);
 
		QCryptographicHash krypo(QCryptographicHash::Sha1);
		const long blockSize = 8192;
		char block[blockSize];
		memset(block, 0, blockSize);
		fread(block, 1, blockSize, fd);
		long c = fSize;
		while( c > 0) {
 
			krypo.addData(block, (c < blockSize) ? c : blockSize);
			c-=(c < blockSize) ? c : blockSize;
		}
		QByteArray hash = krypo.result();

FILE * fd = fopen(fileName.toAscii().data(), "rb");
		if (!fd) return;
		
		
		fseek(fd, 0, SEEK_END);
		long fSize = ftell(fd);
		fseek(fd, 0, SEEK_SET);
		
		QCryptographicHash krypo(QCryptographicHash::Sha1);
		const long blockSize = 8192;
		char block[blockSize];
		memset(block, 0, blockSize);
		fread(block, 1, blockSize, fd);
		long c = fSize;
		while( c > 0) {
			
			krypo.addData(block, (c < blockSize) ? c : blockSize);
			c-=(c < blockSize) ? c : blockSize;
		}
		QByteArray hash = krypo.result();

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I just noticed a bug. I guess it takes posting it to find. I'm not fread'ing in the while loop. I'll fix the bug and see if it works, and post the result.

---

Added after 14 minutes:

Ok, this code works if anyone is interested. Also, please let me know if I should not be using fread, fseek, etc. I hope those work on windows (I use Linux and OS X).

fseek(fd, 0, SEEK_END);
		hashee.fSize = ftell(fd);
		fseek(fd, 0, SEEK_SET);
 
		QCryptographicHash krypo(QCryptographicHash::Sha1);
		const long blockSize = 8192;
		char block[blockSize];
		long c = hashee.fSize;
		while( c > 0) {
			fread(block, 1, (c < blockSize) ? c : blockSize, fd);			
			krypo.addData(block, (c < blockSize) ? c : blockSize);
			c-=(c < blockSize) ? c : blockSize;
		}
		QByteArray hash = krypo.result();

fseek(fd, 0, SEEK_END);
		hashee.fSize = ftell(fd);
		fseek(fd, 0, SEEK_SET);
		
		QCryptographicHash krypo(QCryptographicHash::Sha1);
		const long blockSize = 8192;
		char block[blockSize];
		long c = hashee.fSize;
		while( c > 0) {
			fread(block, 1, (c < blockSize) ? c : blockSize, fd);			
			krypo.addData(block, (c < blockSize) ? c : blockSize);
			c-=(c < blockSize) ? c : blockSize;
		}
		QByteArray hash = krypo.result();

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[wysota]

Why do you complicate things?

QCryptographicHash crypto(QCryptographicHash::Sha1);
QFile file(fileName);
file.open(QFile::ReadOnly);
while(!file.atEnd()){
  crypto.addData(file.read(8192));
}
QByteArray hash = crypto.result();

QCryptographicHash crypto(QCryptographicHash::Sha1);
QFile file(fileName);
file.open(QFile::ReadOnly);
while(!file.atEnd()){
  crypto.addData(file.read(8192));
}
QByteArray hash = crypto.result();

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[pyramation]

@wysota :

Thanks for the tip!