R devel - Sep 2018 - Bug 17432 in readLines with R >= 3.5.0 still a problem

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

Thanks, I responded to this on bugzilla.
On Wed, Sep 12, 2018 at 9:04 AM Chris Culnane
<christopher.culnane at 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
>
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