[Rd] Rscript -e EXPR fails to launch if stdin is closed

[peter dalgaard]

He! 

Yes, that looks like a blunder.

mkstemp() returns -1 on failure, not 0, so the test on ifd (and I suppose also the one on ifp) is wrong. And of course, once you close file descriptor 0, mkstemp() chooses the 1st available fd, i.e. 0, for its return value.

-pd

> On 9 Oct 2022, at 20:25 , Henrik Bengtsson <henrik.bengtsson using gmail.com> wrote:
> 
> Rscript fails to launch if the standard input (stdin) is closed, e.g.
> 
> $ Rscript --vanilla -e 42 0<&-
> Fatal error: creating temporary file for '-e' failed
> 
> This appear to only happen with `-e EXPR`, e.g. it works when doing:
> 
> $ echo "42" > script.R
> $ Rscript --vanilla script.R 0<&-
> [1] 42
> 
> and:
> 
> $ R --vanilla 0<&-
> R version 4.2.1 (2022-06-23) -- "Funny-Looking Kid"
> Copyright (C) 2022 The R Foundation for Statistical Computing
> Platform: x86_64-pc-linux-gnu (64-bit)
> ...
>> 
> 
> 
> TROUBLESHOOTING:
> 
> $ strace Rscript --vanilla -e 42 0<&-
> execve("/home/hb/shared/software/CBI/R-4.2.1-gcc9/bin/Rscript",
> ["Rscript", "--vanilla", "-e", "42"], 0x7fff9f476418 /* 147 vars */) =
> 0
> brk(NULL)                               = 0x5625ca9e6000
> arch_prctl(0x3001 /* ARCH_??? */, 0x7fff23b4d260) = -1 EINVAL (Invalid argument)
> ...
> fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0), ...}) = 0
> write(1, "Fatal error: creating temporary "..., 53Fatal error:
> creating temporary file for '-e' failed
> ) = 53
> exit_group(2)                           = ?
> +++ exited with 2 +++
> 
> which points to src/unix/system.c:
> 
> ifd = mkstemp(ifile);
> if (ifd > 0)
>    ifp = fdopen(ifd, "w+");
> if(!ifp) R_Suicide(_("creating temporary file for '-e' failed"));
> 
> 
> One rationale for having closed standard files (including stdin) is to
> avoid leaking file descriptors, cf.
> https://wiki.sei.cmu.edu/confluence/display/c/FIO22-C.+Close+files+before+spawning+processes
> and https://danwalsh.livejournal.com/53603.html.  The background for
> reporting on this was that `system()` fails to work in processx
> spawned processes, which closes the standard files by default in
> processx (<= 3.7.0).
> 
> Best,
> 
> Henrik
> 
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-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
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