Problems processing incorrect LangAlt values

[postscript-dev]

Describe the bug

The processing problems fall into four categories.

1. No language value
2. Empty language value
3. Mismatched and/or incorrect positioning of quotation marks
4. Invalid characters in language part

To Reproduce

The problems have been observed on the old-master and the 0.27-maintenance branches (though expected on previous branches also).

1. No language value
   This causes a segmentation fault when running

exiv2 -M "set Xmp.dc.title lang= test1-1" any_image.jpeg
exiv2 -M "set Xmp.dc.title lang=\" test1-2" any_image.jpeg

This applies to any LangAlt tag and any image.

2. Empty language value
   This is found when running

exiv2 -M "set Xmp.dc.title lang=\"\" test2" any_image.jpeg

This applies to any LangAlt tag and any image.

3. Mismatched and/or incorrect positioning of quotation marks
   e.g.

exiv2 -M "set Xmp.dc.title lang=\"\"test3-1" any_image.jpeg

exiv2 -M "set Xmp.dc.title lang=\"test3-2" any_image.jpeg

exiv2 -M "set Xmp.dc.title lang=\"en-UK test3-3" any_image.jpeg
exiv2 -M "set Xmp.dc.title lang=en-US\" test3-4" any_image.jpeg

exiv2 -M "set Xmp.dc.title lang=test3-5\"" any_image.jpeg
exiv2 -M "set Xmp.dc.title lang=test3-6\"\"" any_image.jpeg

This applies to any LangAlt tag and any image.

4. Invalid characters in language part
   e.g.

exiv2 -M "set Xmp.dc.title lang=en-UK- test4-1" any_image.jpeg
exiv2 -M "set Xmp.dc.title lang=en=UK test4-2" any_image.jpeg

This applies to any LangAlt tag and any image.

Expected behavior

Exiv2 is expected to cope with a LangAlt statement even if it is not well formed - usually by throwing an exception. The examples in 2) and 3) are accepted and returned by the API, giving the impression that they are valid.

Desktop (please complete the following information):

• OS: Windows 10 (MinGW64 on MinGW/MSYS2) - expected on all
• Compiler & Version: g++.exe (Rev6, Built by MSYS2 project) 10.2.0
• Compilation mode and/or compiler flags: Standard CMakeLists.txt values

Additional context

The problem occurs because of issues in the src/value.cpp file, namely the

int LangAltValue::read(const std::string& buf);

function.

1. No language value
   The segmentation fault is due to not checking the result of

std::string::size_type pos = buf.find_first_of(' ');

2. Empty language value
   By not checking if the language is empty, this value is added into LangAltValue's ValueType and the xmpsdk does not filter this out. I don't think this is allowed under the Xmp specification but others may know better. Using the above example,

$ exiv2 -px any_image.jpeg
### <SNIP>
Xmp.dc.title                                 LangAlt     1  lang="" test2

3. Mismatched and/or incorrect positioning of quotation marks
   Pairs of double quotes are accepted around the outside of the language value.

4. Invalid characters in language part
   The accepted language value is defined in IEFT RFC3066 and I think that it should only contain A-Z (either case), 0-9 and one '-'.

[postscript-dev]

I will look at this more tomorrow.

Also, the templates used when posting an issue are missing. They were stored in the master branch and when this was renamed to old-master, it looks like the setting has not transferred.
You can find the templates here.

[clanmills]

@postscript-dev If I grant you write access to our repos, can you deal with this?

Please read this to understand what's going on with master/old-master. #1466 (comment)

Here's my situation. I worked 14 hours/day last week and again this week on BMFF support. #1475 (comment)

After that I have to ship Exiv2 v0.27.4 RC1 on 2021-03-31. #1018 (comment)

I was 70 in January and the plan was to retire.

[postscript-dev]

@postscript-dev If I grant you write access to our repos, can you deal with this?

Please read this to understand what's going on with master/old-master. #1466 (comment)

Yes, I intended to submit - hopefully today. I posted so that I could reference this in the testing and commit message and didn't intend to burden you with the work.

Here's my situation. I worked 14 hours/day last week and again this week on BMFF support.#1473

I was 70 in January and the plan was to retire.

Thank you for all your hard work, it is appreciated.

[clanmills]

@postscript-dev That's the man, Mr PostScript. Thanks. I'll open the repos now. I know you'll treat it with the respect it deserves. Welcome aboard.

When you submit the PR, I'll review and approve. The PR will merge when the CI is green.