A callback for CGDataProvider around the file pointer

CGDataProvider+FILEPointer.c

#include <CoreGraphics/CoreGraphics.h>

static size_t FILEGetBytesCallback(void * __nullable info, void *  buffer, size_t count)
{
	if (info == NULL) {
		return 0;
	}
	FILE *fInfo = info;
	size_t retVal = fread(buffer, 1, count, fInfo);
	return retVal;
}

static off_t FILESkipForwardCallback(void * __nullable info, off_t count)
{
	if (info == NULL) {
		return 0;
	}
	FILE *fInfo = info;
	off_t start_position = ftello(fInfo);
	fseeko(fInfo, count, SEEK_CUR);
	off_t end_position = ftello(fInfo);
	return (end_position - start_position);
}

static void FILERewindCallback(void *info)
{
	if (info == NULL) {
		return;
	}
	FILE *fInfo = info;
	rewind(fInfo);
}

static void FILEReleaseCallback(void *info)
{
	if (info == NULL) {
		return;
	}
	FILE *fInfo = info;
	fclose(fInfo);
}

const CGDataProviderSequentialCallbacks FILECallback = {
	0,
	FILEGetBytesCallback,
	FILESkipForwardCallback,
	FILERewindCallback,
	FILEReleaseCallback
};