UA_print() using UA_DateTime does not use time zone properly

[dirk-zimoch]

Description

When printing UA_DateTime with UA_Print(), it prints the time in UTC time zone but indicates the local time zone.
This is quite confusing. Usually, the indicated time zone (e.g. +0200) is calculated into the printed time, see for example the Linux date command.

Background Information / Reproduction Steps

Example code:

#include <stdlib.h>
#include "open62541/client.h"

int main() {
    system("date --iso=seconds");
    UA_String out = UA_STRING_NULL;
    UA_DateTime currentTime = UA_DateTime_now();
    UA_print(&currentTime, &UA_TYPES[UA_TYPES_DATETIME], &out);
    printf("%.*s\n", (int)out.length, out.data);
    return 0;
}

Running it prints for example:

2023-09-25T15:08:32+02:00
2023-09-25 13:08:32.237 (UTC+0200)

The first line (printed by date) indicates time zone +02:00 and includes it in the printed time. The printed time is local time.
The second line (printed by UA_print) indicates time zone UTC+0200 but does not include it in the printed time. The printed time is UTC, not UTC+0200 as indicated.

I suggest to modify printDateTime() as follows:

 static UA_StatusCode
 printDateTime(UA_PrintContext *ctx, const UA_DateTime *p, const UA_DataType *_) {
     UA_Int64 tOffset = UA_DateTime_localTimeUtcOffset();
-    UA_DateTimeStruct dts = UA_DateTime_toStruct(*p);
+    UA_DateTime localtime = *p + tOffset;
+    UA_DateTimeStruct dts = UA_DateTime_toStruct(localtime);
     char dateString[100];
     UA_snprintf((char*)dateString, 100,
                 "%04u-%02u-%02u %02u:%02u:%02u.%03u (UTC%+05d)",
                 dts.year, dts.month, dts.day, dts.hour, dts.min,
                 dts.sec, dts.milliSec,
             (int)(tOffset / UA_DATETIME_SEC / 36));
     return UA_PrintContext_addString(ctx, dateString);
 }

Used CMake options:

cmake ..

Checklist

Please provide the following information:

• open62541 Version (release number or git tag): v1.3.6
• Other OPC UA SDKs used (client or server):
• Operating system: Red Hat Enterprise Linux 8.8
• Logs (with UA_LOGLEVEL set as low as necessary) attached
• Wireshark network dump attached
• Self-contained code example attached
• Critical issue

[jpfr]

We already use the better encoding for JSON.
We can use the same for the normal _print.

This list gives a good overview on sane date formats:
https://ijmacd.github.io/rfc3339-iso8601/

[jpfr]

On the master branch, we we already pretty-print via the JSON encoding.
So the only place that needs to be adjusted is in the logging:

open62541/plugins/ua_log_stdout.c

Line 89 in 9aafbdb

printf("[%04u-%02u-%02u %02u:%02u:%02u.%03u (UTC%+05d)] %s/%s" ANSI_COLOR_RESET "\t",

[dirk-zimoch]

I have noticed that UA_print has disappeared from the master branch. That‘s one of the reasons why I prefer the 1.3 branch.

[jpfr]

No, it has not disappeared. Right here:

open62541/include/open62541/types.h

Line 1209 in 9aafbdb

UA_print(const void *p, const UA_DataType *type, UA_String *output);

Just we reuse the JSON encoding now also for pretty-printing.