[Rd] available.packages function and UNC paths

[Tomas Kalibera]

On 4/21/22 21:05, Kevin Ushey wrote:
> FWIW, at least as far as R is concerned, you should be able to use a
> file URI with a UNC path. For example, the following works for me:
>
> repopath <- tempfile("minicran-")
> dir.create(repopath)
> repopath <- normalizePath(repopath, winslash = "/", mustWork = TRUE)
> miniCRAN::makeRepo("renv", path = repopath)
>
> uncpath <- paste0("file:////localhost/c$", substring(repopath, 3L))
> options(repos = c(local = uncpath))
> available.packages()
> install.packages("renv", type = "source")
>
> In this example, the call to available.packages() succeeds for me. I'm
> not sure if miniCRAN itself supports such URIs consistently, though. I
> agree that using a mapped letter drive is the simplest workaround.

Thanks, Kevin, for the nice repro and for checking that 
available.packages() actually handles the UNC path correctly (the 
4-slash form).

The 2-slash form works as well:

uncpath <- paste0("file://localhost/c$", substring(repopath, 3L))

The form Mark observed doesn't, but from my reading it is not a valid one:

uncpath <- paste0("file://\\\\localhost\\c$", substring(repopath, 3L))

Best
Tomas

https://en.wikipedia.org/wiki/File_URI_scheme
https://datatracker.ietf.org/doc/html/rfc8089#appendix-E.3

> Best,
> Kevin
>
> On Thu, Apr 21, 2022 at 6:26 AM Tomas Kalibera <tomas.kalibera using gmail.com> wrote:
>>
>> On 4/6/22 18:07, mark.lee--- via R-devel wrote:
>>> Hello,
>>>
>>> I'm responsible for maintaining a mirrored internal CRAN repository for my organization. We have a script that uses the miniCRAN library to add and update packages within the repository and since the repository is stored on a network drive I have to use UNC paths when calling miniCRAN functions such as this:
>>>
>>> updatePackages(path = '\\\\my-network-drive.net\\repos\\packages', ...)
>>>
>>> updatePackages function in turns call pkgAvail, another miniCRAN function, which calls available.packages and then read.dcf function. However I discovered that this line in available.packages transforms the UNC path to a form that read.dcf can't use:
>>>
>>> if (startsWith(repos, "file:///")) {tmpf <- paste0('/', substring(repos, 8L), "/PACKAGES")
>>>
>>> This line transforms my UNC path to //\\\\my-network-drive.net\\repos\\packages, which read.dcf can't use. During debugging I found that pkgAvail transformed my UNC path to 'file:///\\\\ my-network-drive.net\\repos\\packages' and that is the path being passed to available.packages. To fix my issue I re-defined my own available.packages function and changed the line to:
>>>
>>> if (startsWith(repos, "file:///")) {tmpf <- paste0('/', substring(repos, 10L), "/PACKAGES")
>>>
>>> This way the UNC path being passed to read.dcf will be '/\\my-network-drive.net\\repos\\packages', which read.dcf can use. I'm wondering if similar changes can be made in the available.packages function for the next R release to automatically detect UNC paths and modify it so that it can work with UNC paths.
>> R does not support UNC paths, even though they work in some functions
>> (as stated at least in R-intro documentation). You can use e.g. a mapped
>> drive as a reliable work-around.
>>
>> Transforming the file URIs is tricky enough even without UNC support,
>> and as UNC is only used on Windows, and there is an easy work-around,
>> support for it in update.packages would have very low priority. The cost
>> is not only implementing it, but also maintaining and testing. Still, to
>> increase the chances, you can submit a bug (wishlist) report to R
>> bugzilla, referring only to base R packages (so not e.g. miniCRAN) and
>> add a well-tested patch to be considered.
>>
>> Best
>> Tomas
>>
>>> Thanks,
>>>
>>> Mark
>>>
>>>
>>>
>>>
>>>
>>>
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>>>
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