Fix header line generation for CSV data export

[elfring]

Fix header line generation for CSV data export

[elfring]

💭

• The concatenation order can be adjusted for the delimiter.
• How do you think about to mark any field as “inactive” by default?

[rewolff]

I think the default "field list" contains "spacer" so it prints that field in the results. And it puts a header on top. It takes a lot of code to fix that and it is currently "ok" in that an empty field prints with an empty header.

[elfring]

… it is currently "ok" in that an empty field prints with an empty header.

I disagree with this detail because I observed that the column numbers would be different between the header and subsequent record sets.

[rewolff]

Make it easy for me to verify that. Paste output here.

[elfring]

Do you find a test command (like the following) helpful for further clarification of involved issues? 🤔

Sonne:…/Bau/mtr/console # my_file=/tmp/mtr-test-20220914.csv && ./mtr --report-cycles 2 --csv localhost > ${my_file} && head -n 1 ${my_file} | tr ',' '\n' | wc -l && tail -n 1 ${my_file} | tr ',' '\n' | wc -l
…

[mroe1234]

I'm going to agree that it is /not/ ok to have empty fields. the CSV output is useful for programmatic uses and having a literal space as a header 1. doesn't even really make sense to begin with, and 2. can cause weirdness with tools farther down the pipeline.

[rewolff]

Stuff seems to align correctly. There is just a , at the end of the header line.

If you provide a patch to remove that , I'll accept it.
If you provide a patch to remove the empty header and "0" column below it, I'll accept it.