Simplify cr_get_header_byte_range() + possible efficiency improvment? about createrepo_c

[dralley]

Separately: this (calculating the header byte range) kind of feels like functionality that librpm ought to provide rather than be implemented in createrepo_c. createrepo_c shouldn't be in the business of parsing RPM files and making assumptions about their structure?

[j-mracek]

I think it sound reasonable to remove part of the code in createrepo_c and replace it by calling function from rpm-libs.

In the first place we have to investigate whether both functions returns compatible outputs.

In the second part we have to ask RPM team whether they would expose headerSizeof() as API. May I ask you @pmatilai for an opinion?

[dralley]

I think it's already exposed? It's listed in the documentation.

[dralley]

@pmatilai see discussion

[dralley]

Maybe the reason is that there isn't a version of rpmReadPackageFile() / rpmReadHeader() that works with the signature header? If you can't calculate the size / padding, you can't finish the calculation. But you could probably still simplify it.

[dralley]

I did eventually figure out the magic constants, I'll make a PR eventually to clean the code up a bit.

[dralley]

The fact that there's no way to get back a pair of signature and normal headers, and that the API merges the headers together, makes this impossible.