Add infra_libs as a bootstrap dependency.

infra_libs/time_functions/README.md

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-# A README ON TIME
-
-[TOC]
-
-## ABOUT THIS DOCUMENT
-
-This is a document intended to persuade you, in the course of your computer
-doings, to use a particular representation of time called *stiptime*. Why a
-particular representation of time, and why so staunch about it? The main reason
-is that time is not handled well by libraries in any programming language, and
-misuse leads to subtle bugs. Like memory allocators, representations of time are
-not something application developers give much thought to. Unlike memory
-allocators, you cannot expect your time libraries to "just work." This leads to
-a wide class of bugs that are unintuitive, difficult to anticipate, and
-difficult to test for. stiptime has been designed to avoid many of these
-pitfalls. For a large number of time-related tasks, stiptime just works.
-
-If reading this document causes your head to spin, it has achieved its goal. Use
-stiptime and go on with your day.
-
-## STIPTIME VS BIZARRO TIME
-
-### stiptime
-
-stiptime is a contemporary terrestrial time format meant to reduce the number of
-time-related bugs in computer programs. It makes certain compromises to be
-easier to implement on most operating systems and programming languages circa
-2015-07-10T22:54:32.0Z.
-
-- stiptime is for absolute times: stiptime is meant to represent the absolute
-  (instead of relative) time an event happened. It is not intended for durations
-  or for local representations of time (it will not tell you where the sun is in
-  the sky).
-- stiptime is terrestrial: it is not suitable for astronomical calculations or
-  events happening on Mars. It does not account for [relativistic time
-  dilation](https://en.wikipedia.org/wiki/Barycentric_Dynamical_Time) while
-  traveling through the solar system. It is not suitable for comparing clocks
-  across astronomically vast distances.
-- stiptime is contemporary: it is not particularly useful for describing dates
-  in antiquity, such as anything before the invention of Greenwich Mean Time.
-- stiptime is based on UTC, and uses UTC's concept of leap seconds. Many OSes
-  and date libraries [handle leap
-  seconds](https://tools.ietf.org/html/rfc7164#page-3) in a way that make
-  duration computations inaccurate across them. Unfortunately, continuous
-  timescales like [TAI](https://en.wikipedia.org/wiki/International_Atomic_Time)
-  are not easily available on modern OSes. In light of the difficulty of
-  obtaining TAI, stiptime compromises by being based on UTC and urges caution
-  when making duration computations.
-
-#### definition
-
-stiptime's format is UTC represented as follows:
-
-	YYYY-MM-DDThh:mm:ssZ
-
-where
-
-	YYYY: four digit year
-	MM: zero padded month
-	DD: zero padded day
-	hh: zero padded 24hr hour
-	mm: zero padded minute
-	ss: zero padded second, with a required fractional part
-
-You may notice that this is exactly the [ISO 8601 date
-format](http://www.w3.org/TR/NOTE-datetime) with Z used to represent UTC. That's
-because it is! Z is the [nautical
-timezone](https://en.wikipedia.org/wiki/Nautical_time) for UTC. Since 'Zulu' is
-the [NATO phonetic](https://en.wikipedia.org/wiki/NATO_phonetic_alphabet)
-representation of Z, UTC (and by extension stiptime) can also be referred to as
-Zulu time. Z is used instead of +00:00 as it unambiguously signals UTC and not
-"put in any arbitrary timezone here." It is also short and compact.
-
-#### examples of stiptime
-
-- 2015-06-30T18:50:50.0Z    *typical representation*
-- 2015-06-30T18:50:50.123Z    *fractional seconds*
-- 2015-06-30T23:59:60.0Z    *leap second*
-- 2015-06-30T23:59:60.123Z    *fractional leap second*
-
-#### lesser stiptime
-
-Lesser stiptime is to be used only when necessary. Lesser stiptime is Unix time
-or POSIX time, "fractional seconds since the epoch, defined as
-1970-01-01T00:00:00Z. Seconds are corrected such that days are exactly 86400
-seconds long." The reason stiptime is preferred over lesser stiptime is due to
-that last correction. Since UTC occasionally contains days longer than 86400
-seconds, lesser stiptime cannot encode positive leap seconds unambiguously. The
-consequences of this will be described in a later section. stiptime is preferred
-over lesser stiptime, but lesser stiptime is definitely preferred over bizarro
-time.
-
-### bizarro time
-
-Bizarro time is any time format that is used for absolute time that isn't
-stiptime. Some of these may seem obvious and good, but a later section will show
-their pitfalls.
-
-#### examples of bizarro time
-
-- Tomorrow, 3pm
-- Tuesday 14, July 2015 4:38PM PST
-- 2015-06-30T06:50:50.0PMZ    *not 24hr time*
-- 2015/06/30 18:50:50.0Z    *incorrect separators*
-- 2015-06-30T18:50:50.0    *no Z at the end, unknown timezone*
-- 2015-06-30T18:50:50.0 PST    *PST instead of Z*
-- 2015-06-30T18:50:50.0
-  [America/Los_Angeles](https://en.wikipedia.org/wiki/America/Los_Angeles)
-- 2015-06-30T18:50:50.0+00:00    *using +00:00 instead of Z for UTC*
-- 2015-06-30T18:50:50.0-07:00    *not using UTC*
-- 2015-06-30T18:50:50Z    *no fractional seconds*
-
-## STUCK IN TIME JAIL (THE PITFALLS OF BIZARRO TIME)
-
-Using bizarro time will eventually lead to "fun" and subtle bugs in your
-programs. The inevitability of dealing with all of the contingencies of bizarro
-time (and the libraries that handle it) leads to a profound frustration and
-ennui — this is when you are stuck in *time jail*. The entrances to time jail
-are many, but can be broadly classified into implementation-induced time jail
-and timezone-induced time jail.
-
-### implementation-induced time jail
-
-Writing proper time-handling libraries is hard, which means that most time
-libraries have quirks, unexpected behavior or outright bugs. Some of these even
-occur at the operating system level. This section mostly describes the
-[datetime](https://docs.python.org/2/library/datetime.html) module included in
-the python standard library, but other quirks are documented as well.
-
-#### python 2.7 datetime
-
-- python 2.7 datetime lets you print a date that itself cannot parse
-
-
-	>>> import datetime
-	>>> from dateutil import tz
-	>>> offset = tz.tzoffset(None, -7*60*60)
-	>>> dt = datetime.datetime(2015, 1, 1, 0, 0, 0, tzinfo=offset)
-	>>> a = dt.strftime('%Y-%m-%dT%H:%M:%S %z')
-	>>> a
-	'2015-01-01T00:00:00 -0700'
-	>>> datetime.datetime.strptime(a, '%Y-%m-%dT%H:%M:%S %z')
-	ValueError: 'z' is a bad directive in format '%Y-%m-%dT%H:%M:%S %z'
-
-
-- it lets you print a date that it can parse most of the time, except that one
-  time when you have zero microseconds and then it can't
-
-  See https://bugs.python.org/issue19475 for the problem, and see
-  [zulu.py](https://chromium.googlesource.com/infra/infra/+/master/infra_libs/time_functions/zulu.py)
-  for the 'solution.'
-    
-
-	>>> import datetime
-	>>> a = datetime.datetime(2015, 1, 1, 0, 0, 0, 0).isoformat()
-	>>> b = datetime.datetime(2015, 1, 1, 0, 0, 0, 123).isoformat()
-	>>> a
-	'2015-01-01T00:00:00'
-	>>> b
-	'2015-01-01T00:00:00.000123'
-	>>> datetime.datetime.strptime(a, '%Y-%m-%dT%H:%M:%S')
-	datetime.datetime(2015, 1, 1, 0, 0)
-	>>> datetime.datetime.strptime(b, '%Y-%m-%dT%H:%M:%S')
-	ValueError: unconverted data remains: .000123
-	# okay, let's try with .%f at the end
-	>>> datetime.datetime.strptime(b, '%Y-%m-%dT%H:%M:%S.%f')
-	datetime.datetime(2015, 1, 1, 0, 0, 0, 123)
-	>>> datetime.datetime.strptime(a, '%Y-%m-%dT%H:%M:%S.%f')
-	ValueError: time data '2015-01-01T00:00:00' does not match format '%Y-%m-%dT%H:%M:%S.%f'
-
-- it can't understand leap seconds
-
-
-	>>> import datetime
-	>>> datetime.datetime(2015, 6, 30, 23, 59, 60)
-	ValueError: second must be in 0..59
-
-- it can't tell you what timezone datetime.now() is
-
-
-	>>> import datetime
-	>>> datetime.datetime.now().tzinfo is None
-	true
-	>>> datetime.datetime.now().utcoffset() is None
-	true
-	>>> datetime.datetime.utcnow().tzinfo is None
-	true
-	>>> datetime.datetime.utcnow().utcoffset() is None
-	true
-	>>> datetime.datetime.now().isoformat()
-	'2015-07-15T15:36:23.591431'
-	>>> datetime.datetime.utcnow().isoformat()
-	'2015-07-15T22:36:28.431225'
-
-- it can't mix timezone aware datetimes with naive datetimes (why have naive
-  datetimes to begin with?)
-
-
-	>>> import datetime
-	>>> from dateutil import tz
-	>>> a = datetime.datetime(2015, 1, 1, 0, 0, 0, tzinfo=tz.tzoffset(None, -7*60*60))
-	>>> b = datetime.datetime(2015, 1, 1, 0, 0, 0)
-	>>> a == b
-	TypeError: can't compare offset-naive and offset-aware datetimes
-
-#### that's okay, I'll just use dateutil
-
-- [dateutil](http://labix.org/python-dateutil) is not part of the standard
-  library
-
-  You'll have to venv or wheel it wherever you go. A (non-leap second aware)
-  stiptime parser is a single line of python and requires nothing more than the
-  standard library. A stiptime formatter is 4 lines, and also requires nothing
-  more than the standard library.
-
-- dateutil can't understand leap seconds
-
-
-	>>> import dateutil.parser
-	>>> dateutil.parser.parse('2015-06-30T23:59:60')
-	ValueError: second must be in 0..59
-
-- parser.parse works great, except when it silently doesn't
-
-  (note, running this example will yield different results depending on your
-  local timezone. lol.)
-
-
-	>>> import dateutil.parser
-	>>> a = dateutil.parser.parse('2015-01-01T00:00:00 PST')
-	>>> b = dateutil.parser.parse('2015-01-01T00:00:00 PDT')
-	>>> c = dateutil.parser.parse('2015-01-01T00:00:00 EST')
-	>>> a.isoformat()
-	'2015-01-01T00:00:00-08:00'		# great!
-	>>> b.isoformat()
-	'2015-01-01T00:00:00-08:00'		# uh...
-	>>> c.isoformat()
-	'2015-01-01T00:00:00'					# uhhhhhhh
-	>>> c == a
-	TypeError: can't compare offset-naive and offset-aware datetimes
-
-#### python 2.7 time
-
-- time.time()'s definition is incorrect
-
-  According to [the python docs](https://docs.python.org/2/library/time.html),
-  time.time() "[returns] the time in seconds since the epoch as a floating point
-  number." Except it doesn't, as (at least on unix) days are corrected to be
-  86400 seconds long. Thus the true definition of time.time() should be "the
-  time in seconds since the epoch minus any UTC leap seconds added since the
-  epoch."
-
-### timezone-induced time jail
-
-These are a collection of gotchas that occur even if your timezone-handling
-libraries are perfect. They arise purely out of not using UTC for internal
-computations.
-
-- dates which represent the same moment in time can have different weekdays or
-  other attributes
-
-
-	>>> import dateutil.parser
-	>>> a = dateutil.parser.parse('2015-06-17T23:00:00 PDT')
-	>>> b = dateutil.parser.parse('2015-06-18T06:00:00 UTC')
-	>>> a == b
-	True
-	>>> a.weekday()
-	2
-	>>> b.weekday()
-	3
-
-- it's easy to write code thinking it's in one timezone when it's really in
-  another
-
-  - pop quiz: what timezone does the AppEngine datastore store times in?
-  - pop quiz: what months does daylight savings take effect in Australia? North
-    America?
-  - pop quiz: what timezone does buildbot write twistd.log in? What timezone
-    does it write http.log in?
-
-
-- you can have timezone un-aware code in a timezone that shifts (PST -> PDT).
-
-  Now you have graphs wrapping back on themselves, systems restarting repeatedly
-  for an hour, or silent data corruption. This is the classic timezone bug.
-
-- ambiguous encoding
-
-  If you're not careful, you can encode dates which refer to two instances in
-  time. The date '2015-11-01T01:30:00 Pacific' or '2015-11-01T01:30:00
-  America/Los_Angeles' refers to *two* distinct times:
-  '2015-11-01T01:30:00-0800' and '2015-11-01T01:30:00-0700'. Imagine an alarm
-  clock or cron job which triggers on that.
-
-- illegal dates that aren't obviously illegal
-
-  The opposite of ambiguous encoding: did you know that '2015-03-08T02:30:00
-  Pacific' doesn't exist? It jumped from 2015-03-08T01:59:59 immediately to
-  2015-03-08T03:00:00.
-
-- what does a configuration file look like where any timezone is allowed?
-
-  You've now required everyone to convert every timezone into every timezone,
-  instead of every timezone into one (UTC):
-
-
-	['2015-06-18T05:00:00+00:00'
-	 '2015-06-17T23:00:00-07:00',
-	 '2015-06-18T06:00:00-10:00',
-	]
-
-### leap second time jail
-
-Finally, there is a small jail associated with errors occurring due to leap
-seconds themselves. Unfortunately, stiptime is *not* immune to these.
-
-- ambiguous unix time
-
-
-	2015-06-30T23:59:59.0Z -> 1435708799.0
-	2015-06-30T23:59:60.0Z -> 1435708799.0
-
-- illegal unix time
-
-  This hasn't happened yet, but if a negative leap second ever occurs, there
-  will be a floating point time which 'never happened.'
-
-- calculating durations using start/stop times
-
-  Of course, calculating durations across leap seconds can cause slight errors,
-  mistriggers or even retriggers. Since they happen infrequently (and TAI is not
-  commonly available), stiptime has chosen to be susceptible.
-
-## CONCLUSION
-
-It is my hope that after reading this document, you will consider stiptime and,
-occasionally, lesser stiptime to be the proper way to represent time in stored
-formats. I firmly believe time should be displayed to humans in their local
-format — but only in ephemeral displays. A local absolute time should never
-touch a disk. Join me in using stiptime and get back some sanity in your life.