problem with applying md5 to data

Wilker Wed, 29 Jun 2011 00:03:51 -0700

Hi guys,

I need to generate a hash from a file, the hash algorithm is here:
http://thesubdb.com/api/


I'm trying to implement it on Objective-C but I'm having really trouble on
it...

This is my current implementation:

//
//  SMSubdbSource.m
//  Subtitle Master
//
//  Created by Wilker Lúcio da Silva on 6/23/11.
//  Copyright 2011 __MyCompanyName__. All rights reserved.
//

#import "SMSubdbSource.h"
#import <CommonCrypto/CommonDigest.h>

@implementation SMSubdbSource

+(NSString *)md5:(NSString *)str {
    const char *cStr = [str UTF8String];
    unsigned char result[16];
    CC_MD5(cStr, (unsigned int) strlen(cStr), result);
    return [NSString stringWithFormat:

@"%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X",
            result[0], result[1], result[2], result[3],
            result[4], result[5], result[6], result[7],
            result[8], result[9], result[10], result[11],
            result[12], result[13], result[14], result[15]
            ];
}

+(NSString *)generateHashFromPath:(NSString *)path {
    const NSUInteger CHUNK_SIZE = 65536;

    NSFileHandle *file = [NSFileHandle fileHandleForReadingAtPath:path];

    if (file == nil) return nil;

    unsigned long fileSize = [[[NSFileManager defaultManager]
attributesOfItemAtPath:path error:nil] fileSize];

    NSMutableData *fileData = [[NSMutableData alloc]
initWithCapacity:CHUNK_SIZE * 2];

    [fileData appendData:[file readDataOfLength:CHUNK_SIZE]];
    [file seekToFileOffset:MAX(0, fileSize - CHUNK_SIZE)];
    [fileData appendData:[file readDataOfLength:CHUNK_SIZE]];

    [file closeFile];

    NSString *dataString = [[NSString alloc] initWithData:fileData
encoding:NSASCIIStringEncoding];

    return [[SMSubdbSource md5:dataString] lowercaseString];
}

@end

It works well if file only contains ASCII simple chars, but the real files
(that contains video binary data) generates wrong hash... I mean the problem
should be when trying to generate the string and MD5 digest from it...

How I can make it work correctly?

---
Wilker Lúcio
http://about.me/wilkerlucio/bio
Kajabi Consultant
+55 81 82556600
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