[Rd] Bug 17432 in readLines with R >= 3.5.0 still a problem

[Jennifer Lyon]

Michael:

I don't see any comments on Bug 17432 (
https://bugs.r-project.org/bugzilla3/show_bug.cgi?id=17432) later than June
1, 2018. Would you please supply a link pointing to the followup to this
discussion on bugzilla?

Thanks.

Jen.

> On Thu Sep 13 14:14:46 CEST 2018 Michael Lawrence wrote:
>
> Thanks, I responded to this on bugzilla.
> On Wed, Sep 12, 2018 at 9:04 AM Chris Culnane
> <christopher.culnane using unimelb.edu.au> wrote:
> >
> > Bug 17432 (https://bugs.r-project.org/bugzilla3/show_bug.cgi?id=17432)
is still a problem when using pipes for IPC.
> >
> > The bug is evident when calling R from another process and trying to
communicate via StdIn. R will buffer the input and not read lines until the
buffer is exceeded or StdIn is closed by the sending process. This prevents
interactive communication between a calling process and a child R process.
> >
> > From a quick look at the source code, it looks like the bug is caused
by only disabling buffering when isatty() returns true for a file
descriptor (connections.c). This fixes the original bug when the script is
run in a terminal, but doesn't help for pipes, which will return false for
isatty().
> >
> > An example R script and python script are provided to demonstrate the
problem:
> >
> > R script (example.r):
> > ================
> > f <- file("stdin")
> > open(f)
> > while(length(line <- readLines(f,n=1)) > 0) {
> >   write(line, stderr())
> > }
> >
> > Python3 script:
> > ============
> > import sys, os, subprocess
> > process = subprocess.Popen(['Rscript', 'example.r'],
stdin=subprocess.PIPE, stdout=subprocess.PIPE)
> > for line in sys.stdin:
> >     process.stdin.write((line + '\n').encode('utf-8'))
> >     process.stdin.flush()
> >
> >
> > Expected Behaviour:
> > Run python script, each line entered is echoed back immediately by the
R script - which is what happens on 3.4.4
> >
> > Observed Behaviiour on >=3.5.0 (include devel):
> > The R script does not process lines as they are sent, it only receives
them when StdIn is closed.
> >
> >
> > Best Regards
> >
> > Chris

	[[alternative HTML version deleted]]