convert a RFC3339 date string into a NSDate object

convertDate.m

#import <Foundation/Foundation.h>

// convert a RFC3399 date (& time) into a NSDate object
// NOTE: This function ignores fractions of a second in the RFC3339
// representation.
NSDate *getDateObject(NSString *rfc3339)
{
    // Date and Time representation in RFC3399:
    // Pattern #1: "YYYY-MM-DDTHH:MM:SSZ"
    //                      1                  
    //  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
    // [Y|Y|Y|Y|-|M|M|-|D|D|T|H|H|:|M|M|:|S|S|Z]
    //
    // Pattern #2: "YYYY-MM-DDTHH:MM:SS.sssZ"
    //                      1                   2
    //  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
    // [Y|Y|Y|Y|-|M|M|-|D|D|T|H|H|:|M|M|:|S|S|.|s|s|s|Z]
    //   NOTE: The number of digits in the "sss" part is not defined.
    //
    // Pattern #3: "YYYY-MM-DDTHH:MM:SS+HH:MM"
    //                      1                   2
    //  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 
    // [Y|Y|Y|Y|-|M|M|-|D|D|T|H|H|:|M|M|:|S|S|+|H|H|:|M|M]
    //
    // Pattern #4: "YYYY-MM-DDTHH:MM:SS.sss+HH:MM"
    //                      1                   2
    //  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8
    // [Y|Y|Y|Y|-|M|M|-|D|D|T|H|H|:|M|M|:|S|S|.|s|s|s|+|H|H|:|M|M]
    //   NOTE: The number of digits in the "sss" part is not defined.

    // NSDate format: "YYYY-MM-DD HH:MM:SS +HHMM".

    NSCharacterSet *setOfT = [NSCharacterSet characterSetWithCharactersInString:@"tT"];
    NSRange tMarkPos = [rfc3339 rangeOfCharacterFromSet:setOfT];
    if (tMarkPos.location == NSNotFound) return nil;

    // extract date and time part:
    NSString *datePart = [rfc3339 substringToIndex:tMarkPos.location];
    NSString *timePart = [rfc3339 substringWithRange:NSMakeRange(tMarkPos.location + tMarkPos.length, 8)];
    NSString *restPart = [rfc3339 substringFromIndex:tMarkPos.location + tMarkPos.length + 8];

    // extract time offset part:
    NSString *tzSignPart, *tzHourPart, *tzMinPart;
    NSCharacterSet *setOfZ = [NSCharacterSet characterSetWithCharactersInString:@"zZ"];
    NSRange tzPos = [restPart rangeOfCharacterFromSet:setOfZ];
    if (tzPos.location == NSNotFound) { // Pattern #3 or #4
        NSCharacterSet *setOfSign = [NSCharacterSet characterSetWithCharactersInString:@"+-"];
        NSRange tzSignPos = [restPart rangeOfCharacterFromSet:setOfSign];
        if (tzSignPos.location == NSNotFound) return nil;

        tzSignPart = [restPart substringWithRange:tzSignPos];
        tzHourPart = [restPart substringWithRange:NSMakeRange(tzSignPos.location + tzSignPos.length, 2)];
        tzMinPart = [restPart substringFromIndex:tzSignPos.location + tzSignPos.length + 2 + 1];
    } else { // Pattern #1 or #2
        // "Z" means UTC.
        tzSignPart = @"+";
        tzHourPart = @"00";
        tzMinPart = @"00";
    }
    
    // construct a date string in the NSDate format
    NSString *dateStr = [NSString stringWithFormat:@"%@ %@ %@%@%@", datePart, timePart, tzSignPart, tzHourPart, tzMinPart];
    NSDate *dateObj = [[NSDate alloc] initWithString:dateStr];
    [dateObj autorelease];
    return dateObj;
}

void testGetDateObject(NSString *rfc3339)
{
    NSLog(@"----------------------------------------");
    NSLog(@"RFC3339 Format: %@", rfc3339);
    NSDate *date = getDateObject(rfc3339);
    NSLog(@"NSDate object: %@", date);
    
    NSString *dateFormat = @"%Y-%m-%d %H:%M:%S %z";
    NSString *dateInDefaultTZ = [date descriptionWithCalendarFormat:dateFormat timeZone:nil locale:nil];
    NSLog(@"Default TZ: %@", dateInDefaultTZ);
    NSTimeZone *aTimeZone = [NSTimeZone timeZoneWithName:@"UTC"];
    NSString *dateInUTC = [date descriptionWithCalendarFormat:dateFormat timeZone:aTimeZone locale:nil];
    NSLog(@"UTC: %@", dateInUTC);
}

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    // insert code here...
    testGetDateObject(@"2010-11-22T12:34:56Z");
    testGetDateObject(@"2010-11-22t12:34:56z");
    testGetDateObject(@"2010-11-22T12:34:56.123Z");
    testGetDateObject(@"2010-11-22t12:34:56.123z");
    testGetDateObject(@"2010-11-22T12:34:56+09:00");
    testGetDateObject(@"2010-11-22t12:34:56+09:00");
    testGetDateObject(@"2010-11-22T12:34:56.123+09:00");
    testGetDateObject(@"2010-11-22t12.34.56.123+09:00");
    testGetDateObject(@"2010-11-22T12:34:56-05:00");
    testGetDateObject(@"2010-11-22T12:34:56.123-05:00");

    [pool drain];
    return 0;
}