compressed CGImage with CGImageDestination truncated after getting bytes

Question

I want to get the compressed data from a CGImageRef to send it over a network connection. To do so, i use a CGImageDestinationRef (CGImageDestinationCreateWithData).

After pulling the Data out of the CFDataRef Object the image misses a couple of rows at the bottom.

Here is what i do (cleaned for reading purpose...):

CFImageRef image = getTheImageRefIWant();

CFMutableDataRef pngData = CFDataCreateMutable (kCFAllocatorDefault, 0);    

CGImageDestinationRef dataDest = CGImageDestinationCreateWithData (pngData, kUTTypePNG, 1, NULL);

CGImageDestinationAddImage (dataDest, image, NULL); //also tried this with options...

CGImageDestinationFinalize (dataDest);

CFIndex len = CFDataGetLength(pngData);

//copy data
unsigned char* m_image = malloc(len);
CFDataGetBytes (pngData, CFRangeMake(0,len), m_image);

//save data - for testing purpose
FILE *file = fopen("/path/test.png", "wb");
fwrite(m_image, 1, len, file);

//adding header and stuff - skipped here...

//send data
send(sockfd, m_image, len, 0);

If i use the CFData Object as NSData Object and save it to disk it does work:

NSData *data = [(NSData *)pngData autorelease];
[data writeToFile:@"/path/test.png" atomically:YES];

but if is use NSDatas byte method, it is the same (truncated image):

NSUInteger len = [data length];
m_image = malloc(len);
memcpy(m_image, (unsigned char*)[data bytes], len);

seems the data in CFData Object seems to be ok. But how to get the bytes properly?

Thanks for any advice.

Answer 1

Have you either fflush()ed or fclose()d the file after writing it? Your data may just be buffered in memory.