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Date: Thu, 20 Feb 2025 16:32:55 +0900
To: cygwin AT cygwin DOT com
Subject: Re: [regression-3.6] Pipe between Cygwin and non Cygwin (CRT/URT)
 randomly loses characters
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From: Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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On Wed, 19 Feb 2025 16:23:41 +0900
Takashi Yano wrote:
> On Wed, 19 Feb 2025 07:59:00 +0100
> Cedric Blancher wrote:
> > Good morning!
> > 
> > Cygwin 3.6.0-0.374.g4dd859d01c22.x86_64 on Win10/AMD64/64bit:
> > 
> > Pipe between Cygwin and non Cygwin (CRT/URT) randomly loses
> > characters. We do not have a reproducer yet, but it is happening at
> > least hourly on our test machines. Sometimes we only get a single
> > character, and sometimes words are missing.
> > 
> > Typically it happens like this:
> > bash -c 'typeset bar="$( powershell -Command ...) ; echo "${bar}""',
> > where bar does not contain the full output
> 
> Please provide full command line that can reproduce your problem.
> I can not see any pipe in above command.
> 
> > Same happens with dash and ksh93.
> > 
> > This does not happen between Cygwin processes, i.e. if I compile a
> > program with UCRT and read from a Cygwin program it fails, and if I
> > compile the same sources against Cygwin and pipe it into a Cygwin
> > program it works.

I believe this issue is same as:
https://cygwin.com/pipermail/cygwin/2025-February/257400.html

I'm trying to reproduce the issue using the test case attached.
However, I still cannot.

Any additional information?

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

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#!/bin/bash
cat > random1024.c <<EOF
#include <unistd.h>
#include <stdlib.h>
#include <time.h>

#define LEN 1024
int main()
{
	unsigned char buf[LEN];
	srand(time(NULL));
	for (int i=0; i<LEN; i++) {
		do {
			buf[i] = (int)((double)rand()/RAND_MAX * 256);
		} while (buf[i] == 0 || buf[i] == '\n');
	}
	write(1, buf, LEN);
	return 0;
}
EOF
x86_64-w64-mingw32-gcc random1024.c -o random1024
while true; do
	a=$(./random1024)
	if [ $(/usr/bin/echo -n "$a" | wc -c) -ne 1024 ]; then
		break;
	fi
done
/usr/bin/echo -n "$a" | xxd
/usr/bin/echo -n "$a" | wc -c

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