Enumerate lines in a large file with memory mapping through NSData

enumerate-lines.m

#import <Foundation/Foundation.h>

typedef void(^LineEnumerator)(NSData *lineData, BOOL *stop);

void enumerateLinesInFileAtURL(NSURL *url, LineEnumerator lineEnumerator) {
    NSError *error = nil;
    NSData *data = [NSData dataWithContentsOfURL:url options:NSDataReadingMappedAlways error:&error];
    if (!data) {
        NSLog(@"Unable to open: %@", error);
        return;
    }

    NSData *separatorData = [@"\n" dataUsingEncoding:NSUTF8StringEncoding];

    BOOL shouldStop = NO;
    NSRange searchRange = NSMakeRange(0, data.length);
    while (!shouldStop && searchRange.length) {
        NSRange separatorRange = [data rangeOfData:separatorData options:0 range:searchRange];
        if (separatorRange.location == NSNotFound) {
            // Imaginary zero-length separator at the end of the input
            separatorRange = NSMakeRange(NSMaxRange(searchRange), 0);
        }
        
        NSRange lineRange = NSMakeRange(searchRange.location, separatorRange.location - searchRange.location);
        NSData *lineData = [data subdataWithRange:lineRange];
        lineEnumerator(lineData, &shouldStop);

        NSInteger advance = lineRange.length + separatorRange.length;
        searchRange.location += advance;
        searchRange.length -= advance;
    }
}



int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSURL *url = [NSURL fileURLWithFileSystemRepresentation:argv[1] isDirectory:NO relativeToURL:nil];
        enumerateLinesInFileAtURL(url, ^(NSData *lineData, BOOL *stop) {
            NSString *lineString = [[NSString alloc] initWithData:lineData encoding:NSUTF8StringEncoding];
            NSLog(@"line: %@", lineString);
        });
    }
    return 0;
}