[Rd] possible internal (un)tar bug

[Martin Maechler]

>>>>> Martin Maechler <maechler at stat.math.ethz.ch>
>>>>>     on Tue, 1 May 2018 16:14:43 +0200 writes:

>>>>> Gábor Csárdi <csardi.gabor at gmail.com>
>>>>>     on Tue, 1 May 2018 12:05:32 +0000 writes:

    >> This is a not too old R-devel on Linux, it already fails
    >> in R 3.4.4, and on macOS as well.

    > and fails in considerably older R versions, too.

    > Basically untar() seems to fail on a connection, but works
    > fine on a plain file name.

Well, there's an easy workaround:   If you want to use a
connection (instead of a simple filename) with  untar() and want
to use compression (as in the example), you
can currently  do that easily when you ensure the connection is
a "gzcon" one :

##=========>  Workaround for now:

## Create :
setwd(tempdir()) ; dir.create("pkg")
cat("this: that\n", file = file.path("pkg", "DESCRIPTION"))
tf <- "pkg_1.0.tar.gz"
tar(tf, "pkg", compression = "gzip", tar = "internal")
unlink("pkg", recursive = TRUE)

## As it is a compressed tar file, use it via a gzcon() connection,
## and both cases work fine:
con <- gzcon(file(tf, open = "rb")) ; (f <- untar(con, list = TRUE))
##     ~~~~~
con <- gzcon(file(tf, open = "rb")) ; untar(con, files = f)
stopifnot(identical(f, "pkg/DESCRIPTION"),
          file.exists(f))
unlink(c(tf,"pkg"), recursive = TRUE) # clean after me


------------

Of course, ideally untar() should do that for us and I'm testing
a simple patch to do that.

Martin