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Re: Undetected fatal errors from redirected print

From: Andrew J. Schorr
Subject: Re: Undetected fatal errors from redirected print
Date: Mon, 29 Nov 2021 17:33:35 -0500
User-agent: Mutt/1.5.21 (2010-09-15)

On Sat, Nov 27, 2021 at 10:33:20AM -0500, Andrew J. Schorr wrote:
> On Sat, Nov 27, 2021 at 04:08:28AM -0500, Miguel Pineiro Jr. wrote:
> > Hi, Andy
> > 
> > On Fri, Nov 26, 2021, at 11:28 AM, Andrew J. Schorr wrote:
> > > Interesting. Do we actually need the goto in efwrite, or can we just
> > > skip the fwrite call if count is 0? That way, we can avoid the ugliness
> > > of testing the first character of `from'. See the attached patch.
> > 
> > Testing the first character of from, I agree, is ugly. Though effective, 
> > it's cryptic and arbitrary.
> > 
> > The goto isn't necessary, but I think it actually makes the code and the 
> > intent very easy to follow: If this condition is true, jump to the flush.
> > 
> > I see two issues with your patch:
> > 
> > 1. If I understand your intent, efwrite should flush when count is 0, but 
> > it doesn't. The flushing conditional expression needs OR-ing with "count == 
> > 0". 
> Well, but the call to efwrite has the has the final argument `flush' set to
> true, so the the "if" condition is going to succeed when rp is non-NULL.
> The stdout case is a bit tricker, since it could fail if it's not a tty.
> So you've got a valid point there if we want to use efwrite to flush stdout
> from close_io. What about stderr?

On 2nd thought, I'd argue that efwrite should actually be factored into
three different functions: efwrite, efflush, and wrerror, as in the
attached patch. That just leaves the question of whether efflush should
be called in close_io for stdout and possibly stderr, which already have
some special fflush error handling.


P.S. I'm getting a "make check" ordering error for the iolint test in the
master branch, but I imagine that's unrelated:

--- iolint.ok   2021-11-21 18:16:26.442106000 -0500
+++ _iolint     2021-11-29 17:30:29.657143000 -0500
@@ -20,9 +20,9 @@
 gawk: iolint.awk:53: warning: `cat' used for output file and output pipe
 gawk: iolint.awk:67: warning: `eval $CMD_TO_RUN' used for input pipe and output

Attachment: efflush.patch
Description: Text document

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