Monday, June 01, 2009
And here I thought dating was easy …
I'm building on the work of indexing my filesystem by indexing all of my email. I have a ton of it spread across various directories and when ever I have to search for something (such as the time I flamed an entire department at FAU on a public mailing list—ah, those were the days), it's a long drawn out ordeal to find it.
Initial stab at the problem is to just index a few email headers, like
To: (and the related
Subject:—the primary headers one would
be interested in.
I decided to tackle one of the harder fields to process
From:. While the format is specified in RFC-822 and RFC-2822, there's still quite a bit of variance in the
format to be annoying.
I was able to squish 23 different formats into four cases:
- email address and real name aren't delimited, in which case, the only thing to parse is the email address;
- email isn't delimited, but the real name is (between parentheses, or quotes), so extract the real name from between the delimeters, and anything that isn't delimited is the email address;
- email is delimited (between angle brackets or square brackets), but the real name isn't, so extract the email address, and anything that isn't delimited is the real name;
- both the email address and real name are delimited, so it's trivial to extract both.
Then, I decided to parse the
Date: header. Now, this
is specified, quite plainly:
5. DATE AND TIME SPECIFICATION 5.1. SYNTAX date-time = [ day "," ] date time ; dd mm yy ; hh:mm:ss zzz day = "Mon" / "Tue" / "Wed" / "Thu" / "Fri" / "Sat" / "Sun" date = 1*2DIGIT month 2DIGIT ; day month year ; e.g. 20 Jun 82 month = "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun" / "Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec" time = hour zone ; ANSI and Military hour = 2DIGIT ":" 2DIGIT [":" 2DIGIT] ; 00:00:00 - 23:59:59 zone = "UT" / "GMT" ; Universal Time ; North American : UT / "EST" / "EDT" ; Eastern: - 5/ - 4 / "CST" / "CDT" ; Central: - 6/ - 5 / "MST" / "MDT" ; Mountain: - 7/ - 6 / "PST" / "PDT" ; Pacific: - 8/ - 7 / 1ALPHA ; Military: Z = UT; ; A:-1; (J not used) ; M:-12; N:+1; Y:+12 / ( ("+" / "-") 4DIGIT ) ; Local differential ; hours+min. (HHMM)
Okay, clear if you're into such things. And from the most recent specification:
date-time = [ day-of-week "," ] date FWS time [CFWS] day-of-week = ([FWS] day-name) / obs-day-of-week day-name = "Mon" / "Tue" / "Wed" / "Thu" / "Fri" / "Sat" / "Sun" date = day month year year = 4*DIGIT / obs-year month = (FWS month-name FWS) / obs-month month-name = "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun" / "Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec" day = ([FWS] 1*2DIGIT) / obs-day time = time-of-day FWS zone time-of-day = hour ":" minute [ ":" second ] hour = 2DIGIT / obs-hour minute = 2DIGIT / obs-minute second = 2DIGIT / obs-second zone = (( "+" / "-" ) 4DIGIT) / obs-zone
Really, the only thing this does is mandate that the year be four digits long, moves to a numeric-only timezone format and clarifies a bit where white space appears, but otherwise, is pretty much the same as the older spec.
So, if I ignore the timezone for now (because the Standard C library has such piss-poor support for it, but that's a rant for another time), the only real issue is handling two or four digit years.
And in poking around the man pages for the various Standard C library
routines, I came across
strptime(), which is the functional
strftime()—instead of converting the time to a
human representation, it'll take a human representation and convert it to a
time value. It isn't a Standard C call, but hey, why not use it for
And it appears that the two-digit/four-digit year isn't a problem for
When a century is not otherwise specified, values in the range [69,99] shall refer to years 1969 to 1999 inclusive, and values in the range [00,68] shall refer to years 2000 to 2068 inclusive; leading zeros shall be permitted but shall not be required.
man page for
Only it blew up when it encounted
Wen, 2 Mar 2005 01:39:42
Okay, make sure I start parsing past the optional day of the week. It
then blew up on
Sat Mar 5 18:58:36 2005.
What the—? That's not even a standard format! And then there
Wed,19 十二月 2001 20:23:05 (
I added the question marks
because I can't determine the character set that was used for the
month—there's nothing in that particular email that even hints
what language it might be ).
And let's not forget
9/8/99 1:01:12 AM Pacific Daylight Time
Fri Jun 28 10:07:44 PDT 2002 or even
Wed 8-Jan-2003 08:24:20.
Oh, and we mustn't forget
Tue, 23 May 100 22:18:56
I found it amazing—one of the more strictly defined fields in an email and yet there still was an amazing amount of garbage to be found (although to be fair, these anomalies account for less than one per cent of all the emails scanned, but when you have thousands of emails, it can still add up).
(And one more interesting note—I did not see one email use the military time zone format.)