What's the simplest way to parse RFC3339 date string in iOS?

Question

Youtube API returns date string in RFC3339 format. I found how to parse it on manual, anyway, this is too long.

- (NSString *)userVisibleDateTimeStringForRFC3339DateTimeString:(NSString *)rfc3339DateTimeString
    // Returns a user-visible date time string that corresponds to the
    // specified RFC 3339 date time string. Note that this does not handle
    // all possible RFC 3339 date time strings, just one of the most common
    // styles.
{
    NSString *          userVisibleDateTimeString;
    NSDateFormatter *   rfc3339DateFormatter;
    NSLocale *          enUSPOSIXLocale;
    NSDate *            date;
    NSDateFormatter *   userVisibleDateFormatter;

    userVisibleDateTimeString = nil;

    // Convert the RFC 3339 date time string to an NSDate.

    rfc3339DateFormatter = [[[NSDateFormatter alloc] init] autorelease];

    enUSPOSIXLocale = [[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease];

    [rfc3339DateFormatter setLocale:enUSPOSIXLocale];
    [rfc3339DateFormatter setDateFormat:@"yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'"];
    [rfc3339DateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];

    date = [rfc3339DateFormatter dateFromString:rfc3339DateTimeString];
    if (date != nil) {

        // Convert the NSDate to a user-visible date string.

        userVisibleDateFormatter = [[[NSDateFormatter alloc] init] autorelease];
        assert(userVisibleDateFormatter != nil);

        [userVisibleDateFormatter setDateStyle:NSDateFormatterShortStyle];
        [userVisibleDateFormatter setTimeStyle:NSDateFormatterShortStyle];

        userVisibleDateTimeString = [userVisibleDateFormatter stringFromDate:date];
    }
    return userVisibleDateTimeString;
}

I can make a function contains this, but I want to know is there pre-defined way on Cocoa foundations or standard C or POSIX library to do this. And I want to use it if there it is. Can you let me know is there more simpler way? Or It will be very appreciate if you confirm this is most simple way :)

Answer 1

The pure stuff-that-comes-with-Cocoa way is exactly what you're doing. You can make this method both shorter and faster by creating the date formatters elsewhere, probably in init, and using/reusing them in this method.

Answer 2

You need two formats because fractional seconds are optional, and the timezone should be Z5, not Z. So you create two formatters with formats

@"yyyy'-'MM'-'dd'T'HH':'mm':'ssX5"
@"yyyy'-'MM'-'dd'T'HH':'mm':'ss.SSSSSSX5"

and try them both. That's obviously for RFC3339; your strings might not be in that format. Glad you didn't ask for RFC822 which is a pain to do correctly. But you should really have a method first that returns NSDate, because most uses don't actually need a string formatted for the user.

Answer 3

I had some problems with parsing RFC 3339 in Obj-c since the fractional seconds and zone seems to be optional.

The most reliable function that I found was this Gist (of which I am not the author): https://gist.github.com/mwaterfall/953664