Base64 Encode File Using NSData Chunks

Answer 1

How are you converting back the base64 data to an image? Some implementations limit the maximum line length they will accept. Try inserting a line break every so many characters.

Answer 2

I wish I could give credit to GregInYEG, because his original point about padding was the underlying issue. With base64, each chunk has to be a multiple of 3. So this resolved the issue:

chunkSize = 3600

Once I had that, the corruption went away. But then I ran into memory leak issues, so I added the autorelease pool apprach taken from this post: http://www.cocoadev.com/index.pl?ReadAFilePieceByPiece

Final code:

// Read data in chunks from the original file
[originalFile seekToEndOfFile];
NSUInteger fileLength = [originalFile offsetInFile];
[originalFile seekToFileOffset:0];

// For base64, each chunk *MUST* be a multiple of 3
NSUInteger chunkSize = 24000;
NSUInteger offset = 0;
NSAutoreleasePool *chunkPool = [[NSAutoreleasePool alloc] init];
while(offset "];
    serializedString = [serializedString substringFromIndex:r.location+7];
    r = [serializedString rangeOfString:@""];
    serializedString = [serializedString substringToIndex:r.location-1];

    // Write the base64 encoded chunk to our output file
    NSData *base64EncodedChunk = [serializedString dataUsingEncoding:NSASCIIStringEncoding];
    [encodedFile truncateFileAtOffset:[encodedFile seekToEndOfFile]];
    [encodedFile writeData:base64EncodedChunk];

    // Cleanup
    base64EncodedChunk = nil;
    serializedChunk = nil;
    serializedString = nil;
    chunk = nil;

    // Update the progress bar
    [self updateProgress:[NSNumber numberWithInt:offset] total:[NSNumber numberWithInt:fileLength]];

    // Drain and recreate the pool
    [chunkPool release];
    chunkPool = [[NSAutoreleasePool alloc] init];
}
[chunkPool release];