[R-pkg-devel] Justification and status of the 100-bytes path length limit.

[Ivan Krylov]

В Fri, 13 Sep 2024 15:00:06 +0200
Iago Bonnici <iago.bonnici using umontpellier.fr> пишет:

>      - Is the 100-bytes paths limitation only supposed to ensure 
> compatilbility with pre-POSIX.1-1998 `tar` files?

There are also the Windows systems. While support for paths longer than
260 characters appeared in Windows 10 build 1607 and exists in modern
versions of R [*], it's not enabled by default on many current systems:

d <- tempfile(); dir.create(d); setwd(d); d
"C:\\Users\\[SNIP]\\AppData\\Local\\Temp\\3\\RtmpodtJLb\\file3fec5fce5feb"

(path <- paste(
 sample(
  c('/', letters, LETTERS),
  256, TRUE,
  c(.05, rep((1-.05)/52, 52))
 ),
 collapse = ''
))

"nJpmTZvEleQsFrgjFzvaNRVHGzSIIgERElnFRRmVKpoZkBkfGJlUpnnPaWYhpELTCQ/djTwBiKCvuG/gEjjnRjisLG/sjfayxYXQCycnU/Uu/xcPhMUCwtFOlttgP/OfWKDZJSjmXgAvIyCVCQmIeUXjvGmntEiSqlUqzZOGQRASSMjUHUN/mdTFWuOlIxy/flbyKhKQnjFEIZrowuswFBWLmMmJNHOfRZLeLtDbOlpR/IdycTiIblkYQS/MYawp"


(dir.create(path, recursive = TRUE))

# [1] FALSE
# Warning message:
# In dir.create(path, recursive = TRUE) :
#   cannot create dir
'nJpmTZvEleQsFrgjFzvaNRVHGzSIIgERElnFRRmVKpoZkBkfGJlUpnnPaWYhpELTCQ\djTwBiKCvuG\gEjjnRjisLG\sjfayxYXQCycnU\Uu\xcPhMUCwtFOlttgP\OfWKDZJSjmXgAvIyCVCQmIeUXjvGmntEiSqlUqzZOGQRASSMjUHUN\mdTFWuOlIxy',
reason 'No such file or directory'

sessionInfo()
# R version 4.3.2 (2023-10-31 ucrt)
# Platform: x86_64-w64-mingw32/x64 (64-bit)
# Running under: Windows Server 2022 x64 (build 20348)

As a test, I have prepared a source package with an exactly 256-byte
maximal path length:

untar('foo_1.0.tar.gz', list = TRUE) |> nchar() |> max()
# [1] 256

I was not able to install it with the internal untar() ("ERROR:
extracted multiple files from ‘foo_1.0.tar.gz’" -- it seems to have
extracted both the long path from the GNU extension and the "dummy"
path stored in the 100-octet 'name' field), but it did work with the
R_INSTALL_TAR='tar' environment variable on Linux. On Windows, it
failed to extract the tarball in a manner similar to the first
experiment when the total path length exceeded 260.

-- 
Best regards,
Ivan

[*]
https://blog.r-project.org/2023/03/07/path-length-limit-on-windows/index.html