RFC timestamp in Flash/AS3

actionscript-3dateflash

I'd like to know if Flash/AS3 has any nice way to convert an AS3 'Date' object to/from rfc-850 timestamp format (as used by HTTP date and last-modified).

This question is very similar to this question about rfc 3339, except it's specific to AS3 and rfc-850.

RFC-850 is like: Thu, 09 Oct 2008 01:09:43 GMT

Best Solution

Alright, so here's a couple of functions to do RFC-802/Date conversion in Flash.

I learned that the Date object doesn't really have any notion of a timezone, and assumes that it is in the local timezone. If you pass an RFC-802 date to the Date() constructor, it parses it everything except the "GMT" timezone token at the end, resulting in the correct time but possibly in the wrong timezone.

Subtracting the current timezone from the parsed Date compensates for this, so a timestamp can do a round-trip with these functions without becoming completely wrong.

(Wouldn't it have been great if somebody had included a timezone property when they were designing the Date class?)

/**
 * Converts an RFC string to a Date object.
 */
function fromRFC802(date:String):Date {
    // Passing in an RFC802 date to the Date constructor causes flash
    // to conveniently ignore the "GMT" timezone at the end, and assumes
    // that it's in the Local timezone.
    // If we additionally convert it back to GMT, then we're sweet.

    var outputDate:Date = new Date(date);
    outputDate = new Date(outputDate.time - outputDate.getTimezoneOffset()*1000*60);
    return outputDate;
}

/** 
 * Converts a Date object to an RFC802-formatted string (GMT/UTC).
 */
function toRFC802 (date:Date):String {
    // example: Thu, 09 Oct 2008 01:09:43 GMT

    // Convert to GMT

    var output:String = "";

    // Day
    switch (date.dayUTC) {
    case 0: output += "Sun"; break;
    case 1: output += "Mon"; break;
    case 2: output += "Tue"; break;
    case 3: output += "Wed"; break;
    case 4: output += "Thu"; break;
    case 5: output += "Fri"; break;
    case 6: output += "Sat"; break;
    }

    output += ", ";

    // Date
    if (date.dateUTC < 10) {
        output += "0"; // leading zero
    }
    output += date.dateUTC + " ";

    // Month
    switch(date.month) {
    case 0: output += "Jan"; break;
    case 1: output += "Feb"; break;
    case 2: output += "Mar"; break;
    case 3: output += "Apr"; break;
    case 4: output += "May"; break;
    case 5: output += "Jun"; break;
    case 6: output += "Jul"; break;
    case 7: output += "Aug"; break;
    case 8: output += "Sep"; break;
    case 9: output += "Oct"; break;
    case 10: output += "Nov"; break;
    case 11: output += "Dec"; break;
    }

    output += " ";

    // Year
    output += date.fullYearUTC + " ";

    // Hours
    if (date.hoursUTC < 10) {
        output += "0"; // leading zero
    }
    output += date.hoursUTC + ":";

    // Minutes
    if (date.minutesUTC < 10) {
        output += "0"; // leading zero
    }
    output += date.minutesUTC + ":";

    // Seconds
    if (date.seconds < 10) {
        output += "0"; // leading zero
    }
    output += date.secondsUTC + " GMT";

    return output;
}

var dateString:String = "Thu, 09 Oct 2008 01:09:43 GMT";

trace("Round trip proof:");

trace(" RFC-802: " + dateString);
trace("Date obj: " + fromRFC802(dateString));
trace(" RFC-802: " + toRFC802(fromRFC802(dateString)));
trace("Date obj: " + fromRFC802(toRFC802(fromRFC802(dateString))));
trace(" RFC-802: " + toRFC802(fromRFC802(toRFC802(fromRFC802(dateString)))));
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