I was looking at the response headers for my GMail account and noticed that the date Fri, 01 Jan 1990 00:00:00 GMT shows up as the value for "Expires" over and over again. I suppose this is just an easy constant to make sure the browser understands this is past its freshness date. But is there any significance to that particular date? One might as easily have used the same date in 2000, or 1970, or whatever. It's not quirky enough to be someone's birthday or date of college graduation or anything personal like that. Maybe it's just arbitrary, but I was wondering if someone has a good explanation why that particular date was chosen.
No significance, any date in the past will do the job, someone just picked an arbitrary past date. This is so your browser won't cache the page :)
Your browser understands "this is good until..." oh, I need to fetch it again, every time in this case.
Related
I am working with an API that generates time periods based on a configured set of parameters.
So for example, I can specify I want 12 one month periods starting Jan 1st at midnight, and therefore the API will generate 12 monthly periods
01 Jan 2016 00:00:00 – 31 Jan 2016 23:59:59
01 Feb 2016 00:00:00 – 28 Feb 2016 23:59:59
Through to
01 Dec 2016 00:00:00 – 31 Dec 2016 23:59:59
Now the API expects a start date param supplied for the sequence of periods to be an ISO formatted string in UTC. So I’m currently in the UK, therefore if I choose to start the monthly periods from Jan 1st 2016 this would be 2016-01-01T00:00:00Z and is what I supply to the API call I am making to say when the first instance of my monthly periods should begin.
So now if I view the start and end dates of the generated monthly periods via the API, I will see them come back as
2016-01-01T00:00:00Z - 2016-01-31T23:59:59Z
2016-02-01T00:00:00Z - 2016-02-28T23:59:59Z
Etc to
2016-12-01T00:00:00Z - 2016-12-31T23:59:59Z
Something struck me about these generated periods and that is I want them to begin at midnight for where I currently am, but a period that is affected by GMT Daylight Time, so say my April period will look like so in the generated period from the API
2016-04-01T00:00:00Z - 2016-04-30T23:59:59Z
Parsing the start date for the above into a date object for viewing in the client (on my machine) will show up as
Fri Apr 01 2016 01:00:00 GMT+0100 (GMT Daylight Time)
So it’s saying that period starts at 1am and not midnight.
Now say if I wanted 12 months to be generated from 1st Jun when Daylight Savings is in effect.
My client side code currently will supply a start date to the API of 2016-05-31T23:00:00Z. This causes the API to generate start dates for each monthly period as being
2016-05-31T23:00:00Z - 2016-06-31T22:59:59Z (June Period)
2016-06-31T23:00:00Z - 2016-07-31T22:59:59Z (July)
Etc to
2017-04-30T23:00:00Z - 2017-05-31T22:59:59Z (May)
But now for a period that is not in GMT Daylight Time, so Jan for example it will show up as
2016-12-31T23:00:00Z - 2017-01-31T22:59:59Z
Meaning my client will see that start date as
Sat Dec 31 2016 23:00:00 GMT+0000 (GMT Standard Time)
So not Jan 1st at 00:00
Does this suggest that the API should know about the users timezone so the period generation logic in the API can factor this is when calculating the start and end dates?
Maybe I'm over thinking things here?!
The only real question I see here is:
Does this suggest that the API should know about the users timezone so the period generation logic in the API can factor this is when calculating the start and end dates?
In general, the answer is YES. Any time you are mapping calendar dates back to specific instants in time, then by definition you must involve time zones. That time zone can be that of the user's, or of some specific business location, or fixed to UTC, but they indeed part of the logic.
Consider that not every calendar date has a valid local "midnight" in every time zone. An example is 2015-10-18 in Sao Paulo Brazil, where the first moment of that day was 1:00 AM due to their spring-forward daylight saving time transition. There are many other examples of this around the world.
The only way to avoid the problem entirely is to not deal in specific times. If you are only working with whole dates, then your code can certainly compute the exact dates of each month without knowing anything about time zones. 2016-01-01 through 2016-01-31 has no awareness of time or time zone. It's only when you try to ask what the current date is, or if now is within that range, or if some other specific instant in time is within that range that you have to start thinking about time zones.
I have problem understanding the following date formate from apiblueprint tutorial
2016-02-05T08:40:51.620Z
I now 2016 is the year 02 is the month 05 is the date and 08:40:51 is the time but I dont understand the last part .620Z.
Can some one explain it for me. I wanted to find out AM or PM of the time using javascript from the date using javascript and not sure whether the formate is 12 or 24 hours.
Thanks
First of all, API Blueprint doesn't require you to use any particular Date format; you are free to use whatever you want to.
The format used in the tutorial is the standard ISO 8601 format: .620 is the number of miliseconds, and Z designates a Zulu timezone, meaning UTC.
I really have a basic understanding of the world time zone clock. I looked at this site (http://www.pobox.com/helpspot/index.php?pg=kb.page&id=256) and this helps explain how to adjust the time according to its GMT offset on the date in email headers. But I just want clarification since I can't find it anywhere else.
Say you have information like this:
Thu, 27 Dec 2001 07:02:12 -0800 (PST)
Is it possible for a GMT value to be a value not divisible by 100 in email headers? In other words, is it possible for it to show (the 42 was arbitrary chosen):
Thu, 27 Dec 2001 07:02:12 -0842 (PST)
For those of you curious in what I'm doing, I'm trying to write a method that standardizes the time and date according to the time zone listed in email headers. You could argue that many programming languages support an automatic date and time conversion but I want to also know.
Thanks.
It is indeed possible. Currently, there are offsets that contain 30 and 45 in the last two digit positions. The Marquesas Islands is offset by -0930, and Nepal by +0545.
I have a field containing what should be a UNIX time stamp. As an example one value is 1408675380
Now when I do various online conversions, it shows the right day (22nd August) but shows the incorrect time. It should be around 21:00 or so but instead shows 02:43:00 GMT
Likewise, 1408676520 shows the correct day (22nd August) but instead of showing a time of around 22:00/23:00 it shows 03:02:00 GMT
I have no control over the data at all - just wondering if there's something obvious I'm missing?
1408849260 - Sunday, August 24th 2014, 03:01:00 (GMT) - Correct day, around 18 hours too early
1408850640 - Sunday, August 24th 2014, 03:24:00 (GMT) - Correct day, around 18 hours too early
Thanks,
JJ
Is your data in some other timezone than GMT ? something like GMT-5 (america west cost maybe ?)
I've been working on facebook application. But I've faced with strange bug(?).
It I'm trying to get detailed info about any event using graph api start_date differs from the one if I'm trying to get it using fql. for example:
https://graph.facebook.com/209798352393506/ - start date is 2011-05-26T19:00:00
https://api.facebook.com/method/fql.query?query=select%20eid%2C%20name%2C%20tagline%2C%20pic%2C%20host%20%2C%20start_time%20from%20event%20where%20eid%20%3D209798352393506 - start time is 1306461600. Which in human readable format equals to Fri, 27 May 2011 02:00:00 GMT.
As you can see difference between got dates is 5 hours. Somtimes I'm getting dates which differ for 8 hours, sometimes - 6.
Correct date is the first one:
http://www.facebook.com/events/209798352393506/
I can't figure out what happens. All events I'm trying to view are from Denmark. My timezone is Europe/Kiev. Difference is 1 hour.
Is this a facebook's bug? Or documented feature? Or am I doing something wrong?
Link to the documentation or another answer in stackoverflow would be enough.
Here is two events
http://www.facebook.com/events/290600150977115/ - starts on 2012-03-22 at 20:00
http://www.facebook.com/events/289501924395338/ - starts on 2012-03-03 at 21:00
But. Using FQL I'm getting that first event starts on 2012-03-23 at 04:00. Difference is 8 hours. And the second one starts on 2012-03-04 at 06:00. In this case difference is 9 hours. Why???
It was because of daylight saving time.
Time difference between me and facebook(Los Angeles) sometimes was 8 sometimes 9 hours, because there was a moment when Denmakr alredy changed their time to summer time and los angeles - not.
The problem occured when event started "in winter time" and finished in summer time. In this case I needed to add one hour.
Facebook is weird.
From /fql/insights/
The end of the period during which the metrics were collected, expressed as a unix time (which should always be midnight, Pacific Daylight Time) or using the function end_time_date() which takes a date string in 'YYYY-MM-DD' format.
2011-05-26T19:00:00 ===> 2011-05-26T19:00:00 PDT ===> Fri, 27 May 2011 02:00:00 GMT.