convert time/date from HTTP-header [partially SOLVED]

[xint]

I have a Date string from a HTTP-header "Thu, 20 Feb 2025 16:09:13 GMT", I have to compare against a more regular TimeDate-String, which is "2025-03-06".

Does someone has an idea how to convert the HTTP string in a more simple way then using lots of pos, copy's and length's ?


Thanks !

[Nimbus]

Well there are certainly methods to parse/format datetimes in the RTL

Code: Pascal  [Select][+][-]

1. program Hello;
2.  
3. uses
4.   SysUtils, DateUtils;
5.  
6. var
7.   InputStr, OutputStr: String;
8.   DateTime: TDateTime;
9.  
10. const
11.   RFC1123_TimePattern = 'ddd, dd mmm yyyy hh:nn:ss "GMT"';
12.  
13. begin
14.   InputStr := 'Thu, 20 Feb 2025 16:09:13 GMT';
15.   DateTime := ScanDateTime(RFC1123_TimePattern, InputStr);
16.   OutputStr := FormatDateTime('yyyy-MM-dd', DateTime);
17.   Writeln(OutputStr);
18. end.

[cdbc]

Hi
edit: Nimbus beat me to it, with a better answer...
Yes, use a "poor man's state-machine", i.e.: you write a function with a simple state-parser inside...
Being an internet-date-format, I don't think it'll change format on you...
Should be doable ...and pretty reusable 
You'll need some good sample specimens to practice on, I'd say 25..50 different inet-datestamps, should do it for a start...

1) analyze the input string, you've got 1 - need more for precision
2) run through the string char by char
3) depending on where you are in the string, pick out the relevant string
4) lookup in a couple of arrays and convert to your format
5) when done, assemble the return string - and Bob's your uncle

Regards Benny

[MarkMLl]

I am by no means an expert,  but I think that https://www.freepascal.org/docs-html/rtl/sysutils/strtodatetime.html with the format settings appropriately localised is probably the way to do it.

I'd caution against making any assumptions about time resolutions finer than a second, since FPC (and Delphi before it) considers the ISO to be wrong.

MarkMLl

[xint]

I am by no means an expert,  but I think that https://www.freepascal.org/docs-html/rtl/sysutils/strtodatetime.html with the format settings appropriately localised is probably the way to do it.

I'd caution against making any assumptions about time resolutions finer than a second, since FPC (and Delphi before it) considers the ISO to be wrong.

MarkMLl

StrToDateTime constantly fails with this particular string - I already wasted a significant amount of time to give this approach a try. Thank you anyway !

[xint]

Well there are certainly methods to parse/format datetimes in the RTL

So glad to see your reply. Thanks a million !

[MarkMLl]

StrToDateTime constantly fails with this particular string - I already wasted a significant amount of time to give this approach a try. Thank you anyway !

Which suggests that the long-format for date and times chosen by your OS's locale is wrong. since the function I cited allows you to override that with a parameter (i.e. does not change the program's defaults) it should be possible to fix it.

MarkMLl

[TRon]

Code: Pascal  [Select][+][-]

1.   OutputStr := FormatDateTime('yyyy-MM-dd', DateTime);
2. end.

In case waning to make sure that the separator is actually going to be "-" ...

Code: Pascal  [Select][+][-]

1.   OutputStr := FormatDateTime('yyyy"-"MM"-"dd', DateTime);

.. otherwise the locale is able to alter that to whatever it is configure to use.

[xint]

Unfortunately I have to take up this problem again.
Since I switched back to my German development system, Nimbus solution fails - I assume it's because of the different short names for months and days for each language.

If so, the final software would encounter the same problem depending on where in the world it runs. Is there any way to override the default language settings of the operating system?

[xint]

finally found the solution:

Code: Pascal  [Select][+][-]

1. LCID_English = 2057; // british
2. GetLocaleFormatSettings(LCID_English,fs);
3.  

[xint]

I have a Date string from a HTTP-header "Thu, 20 Feb 2025 16:09:13 GMT", I have to compare against a more regular TimeDate-String, which is "2025-03-06".

Does someone has an idea how to convert the HTTP string in a more simple way then using lots of pos, copy's and length's ?


Thanks !

[silvercoder70]

Or with Indy...

Code: Pascal  [Select][+][-]

1.   HttpDate := 'Sun, 06 Nov 1994 08:49:37 GMT';
2.   PascalDateTime := InternetTimeToDateTime(HttpDate);
3.  

[wp]

finally found the solution:

Code: Pascal  [Select][+][-]

1. LCID_English = 2057; // british
2. GetLocaleFormatSettings(LCID_English,fs);
3.  

This is Windows-only. If you need a cross-platform solution do this:

Code: Pascal  [Select][+][-]

1. function RFC1123DateTime(s: String): TDateTime;
2. const
3.   MONTH_NAMES: array[1..12] of string = (
4.     'Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'
5.   );
6.   DAY_NAMES: array[1..7] of string = (
7.     'Son', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'
8.   );
9. var
10.   fs: TFormatSettings;
11. begin
12.   fs := DefaultFormatSettings;
13.   fs.ShortMonthNames := MONTH_NAMES;
14.   fs.ShortDayNames := DAY_NAMES;
15.   Result := ScanDateTime('ddd, dd mmm yyyy hh:nn:ss "GMT"', s, fs);
16. end;

[duralast]

Using AWK 

Code: [Select]

$ echo "Thu, 20 Feb 2025 16:09:13 GMT" | awk '{sub(/Jan/,"01");sub(/Feb/,"02");sub(/Mar/,"03");sub(/Apr/,"04");sub(/May/,"05");sub(/Jun/,"06");sub(/Jul/,"07");sub(/Aug/,"08");sub(/Sep/,"09");sub(/Oct/,"10");sub(/Nov/,"11");sub(/Dec/,"12");print $4"-"$3"-"$2}'
2025-02-20
$