Convert a string date to a timestamp

Question

Is there any simple way to convert a RFC HTTP date into a timestamp in Lua?

"Sat, 29 Oct 1994 19:43:31 GMT"

into

783467011

Solution 1

Correcting lhf's example code to account for timezone since os.time() does not have a way to specify the timezone. Also assume all input ends in GMT since this only works with GMT.

s="Sat, 29 Oct 1994 19:43:31 GMT"
p="%a+, (%d+) (%a+) (%d+) (%d+):(%d+):(%d+) GMT"
day,month,year,hour,min,sec=s:match(p)
MON={Jan=1,Feb=2,Mar=3,Apr=4,May=5,Jun=6,Jul=7,Aug=8,Sep=9,Oct=10,Nov=11,Dec=12}
month=MON[month]
offset=os.time()-os.time(os.date("!*t"))
print(os.time({day=day,month=month,year=year,hour=hour,min=min,sec=sec})+offset)

Which gives us 783477811. And we will verify with os.date("!%c") because the ! will make the output in UTC instead of local timezone.

print(os.date("!%c",783477811))
--> Sat Oct 29 19:43:31 1994

Solution 2

If you need to convert the value to a unix timestamp, the code to do so would be this:

-- Assuming a date pattern like: yyyy-mm-dd hh:mm:ss
local pattern = "(%d+)-(%d+)-(%d+) (%d+):(%d+):(%d+)"
local timeToConvert = "2011-01-01 01:30:33"
local runyear, runmonth, runday, runhour, runminute, runseconds = timeToConvert:match(pattern)

local convertedTimestamp = os.time({year = runyear, month = runmonth, day = runday, hour = runhour, min = runminute, sec = runseconds})

Solution 3

The code below does this except that it does not handle timezones:

s="Sat, 29 Oct 1994 19:43:31 GMT"
p="%a+, (%d+) (%a+) (%d+) (%d+):(%d+):(%d+) (%a+)"
day,month,year,hour,min,sec,tz=s:match(p)
MON={Jan=1,Feb=2,Mar=3,Apr=4,May=5,Jun=6,Jul=7,Aug=8,Sep=9,Oct=10,Nov=11,Dec=12}
month=MON[month]
print(os.time({tz=tz,day=day,month=month,year=year,hour=hour,min=min,sec=sec}))

But it prints 783467011. The code below tells us that 1288374211 is a different date:

print(os.date("%c",1288374211))
--> Fri Oct 29 15:43:31 2010
print(os.date("%c",783467011))
--> Sat Oct 29 19:43:31 1994

Solution 4

use luadate, you can install it with luarocks.

date = require 'date'
local d1 = date('Sat, 29 Oct 1994 19:43:31 GMT')                                                                                               
local seconds = date.diff(d1, date.epoch()):spanseconds()
print(seconds)

Solution 5

Arrowmaster's answer above would be perfect if daylight saving time is considered. Also using array seems cleaner.

s="Sat, 29 Oct 1994 19:43:31 GMT"
p="%a+, (%d+) (%a+) (%d+) (%d+):(%d+):(%d+) GMT"
date={}
date['day'],date['month'],date['year'],date['hour'],date['min'],date['sec']=s:match(p)
MON={Jan=1,Feb=2,Mar=3,Apr=4,May=5,Jun=6,Jul=7,Aug=8,Sep=9,Oct=10,Nov=11,Dec=12}
date['month']=MON[date['month']]
date["isdst"] = false  -- new code
offset=os.time()-os.time(os.date("!*t"))
print(os.time(date)+offset)

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Comments

[thangaraj m.d]

what if my dateformat is '"2021-12-16T12:28:21.190344545Z"' and I want to find the difference between epochtime and this UTC time with millisecond resolution?