[R] Test internet presence

[Gregor Gorjanc]

Prof Brian Ripley <ripley <at> stats.ox.ac.uk> writes:
...
> Check out tests/internet.R.  nsl() checks if you can resolve host names, 
> which has worked well enough there.

Thank you prof. Ripley for this pointer. I am posting here the relevant part if
someone does not look at SVN. I would just like to ask why is .Platform$OS.type
== "unix" added to the test? Is nsl() available only on unix like platforms or
... I did not found any specifics in its help page.

if(!capabilities()["http/ftp"]) {
    warning("no internet capabilities")
    q()
}

if(.Platform$OS.type == "unix" &&
   is.null(nsl("cran.r-project.org"))) q()

Does it make any sense to write a function that would use these two tests.

isNetAvailable <- function()
{
  ifelse(!capabilities()["http/ftp"] && 
##         .Platform$OS.type == "unix" && ## ??? 
         is.null(nsl("cran.r-project.org")), 
         FALSE, 
         TRUE)
}

Regards, Gregor