Exiv2

Version of Exiv2: 0.27.3 (and tested HEAD of 0.27-maintenance branch too)

1. Description of problem

A date and time can be written with Exiv2 in IPTC (tags Iptc.Application2.DateCreated and Iptc.Application2.TimeCreated respectively) using a specific format "2020-11-15" and "HH:MM:SS-HH:MM" but when read back (still with Exiv2), it expects another format ("20201115" and "HHMMSS:HHMM" which corresponds to what you wrote here: https://exiv2.org/iptc.html) resulting in following errors being returned: "Unsupported date format" and "Unsupported time format".

Note that if I try to set instead with "20201115" and "HHMMSS:HHMM" format instead, then I get the same errors but this time when setting the IPTC tag. It really seems like the API is not consistent on write and read.

1. More info

Looking quickly into exiv2 code, for instance in `src/value.cpp`, I can see that DateValue::read(const byte* buf, long len, ByteOrder /*byteOrder*/) definitely expects a string of 8-byte string with format "%4d%2d%2d" (similarly for TimeValue::read()). This is the code we hit when we previously set date/time in another format (also with exiv2, I remind) hence get kerUnsupportedDateFormat and kerUnsupportedTimeFormat errors.

But now when I set a new tag, Iptcdatum::setValue(const std::string& value) calls DateValue::read(const std::string& buf) which has the format "%4d-%d-%d".

So basically you have 2 versions of read() for DateValue and TimeValue, and they do something different. And as it turns out, we hit one of the version when writing a new tag, the other when reading tags from existing files. Therefore Exiv2 fails to read some tags it created itself.

src/pngimage.cpp