[R] Good Package(s) for String and URL processing?

[Ralf B]

Are there packages that allow improved String and URL processing?
E.g. extract parts of a URLs such as sub-domains, top-level domain,
protocols (e.g. https, http, ftp), file type based on endings, check
if a URL is valid or not, etc...

I am currently only using split and paste. Are there better and more
efficient ways to handle strings e.g. finding sub-strings or to do
pattern matching?
What packages do you use if you have to do a lot of String processing
and you don't have the option to go to another language such as Perl
or Python?

Thanks,
Ralf