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Perl
IO::Handle::error() can lose read errors
As reported by Ian Jackson in https://bugs.debian.org/1016369 IO::Handle::error() can report 0 when there was an error on the filehandle.
A test case is
perl -MIO::Handle -e 'open X, "<", "." or die $!; $_ = <X>; printf "%s %s\n", X->error(), $!;'
which returns "0 Is a directory" for me on Linux although all reads on the filehandle fail with EISDIR.
I've debugged this a bit and it looks like the error gets cleared in Perl_do_readline() around pp_hot.c:3295 or so with a PerlIO_clearerr() call. I think this is related to reading past EOF or something like that?
While trying to treat a directory as a regular file is something of a corner case (and the result is rather platform dependent), Ian argues that this is an indication of a more general problem where EIO and similar errors can go unnoticed if user code is relying on the IO::Handle::error() method to report them. Of course, creating simple test cases for such errors is difficult if not impossible.
I see #12782 is very similar but hasn't really received much attention. Is this something that should at least be documented as a caveat if it's not fixable?
-----------------------------------------------------------------
---
Flags:
category=library
severity=medium
module=IO::Handle
---
Site configuration information for perl 5.37.3:
Configured by ntyni at Sat Aug 6 17:54:25 BST 2022.
Summary of my perl5 (revision 5 version 37 subversion 3) configuration:
Commit id: 12d173c94b050c244dbb4e2162e29834a9ac3aff
Platform:
osname=linux
osvers=5.17.0-1-amd64
archname=x86_64-linux
uname='linux carme 5.17.0-1-amd64 #1 smp preempt debian 5.17.3-1 (2022-04-18) x86_64 gnulinux '
config_args='-des -Dusedevel'
hint=recommended
useposix=true
d_sigaction=define
useithreads=undef
usemultiplicity=undef
use64bitint=define
use64bitall=define
uselongdouble=undef
usemymalloc=n
default_inc_excludes_dot=define
Compiler:
cc='cc'
ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
optimize='-O2'
cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
ccversion=''
gccversion='11.2.0'
gccosandvers=''
intsize=4
longsize=8
ptrsize=8
doublesize=8
byteorder=12345678
doublekind=3
d_longlong=define
longlongsize=8
d_longdbl=define
longdblsize=16
longdblkind=3
ivtype='long'
ivsize=8
nvtype='double'
nvsize=8
Off_t='off_t'
lseeksize=8
alignbytes=8
prototype=define
Linker and Libraries:
ld='cc'
ldflags =' -fstack-protector-strong -L/usr/local/lib'
libpth=/usr/local/lib /usr/lib/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib
libs=-lpthread -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
libc=libc-2.33.so
so=so
useshrplib=false
libperl=libperl.a
gnulibc_version='2.33'
Dynamic Linking:
dlsrc=dl_dlopen.xs
dlext=so
d_dlsymun=undef
ccdlflags='-Wl,-E'
cccdlflags='-fPIC'
lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'
---
@INC for perl 5.37.3:
lib
/usr/local/lib/perl5/site_perl/5.37.3/x86_64-linux
/usr/local/lib/perl5/site_perl/5.37.3
/usr/local/lib/perl5/5.37.3/x86_64-linux
/usr/local/lib/perl5/5.37.3
---
Environment for perl 5.37.3:
HOME=/home/ntyni
LANG=C
LANGUAGE (unset)
LC_CTYPE=fi_FI.UTF-8
LD_LIBRARY_PATH (unset)
LOGDIR (unset)
PATH=/usr/local/bin:/usr/bin:/bin:/usr/games
PERL_BADLANG (unset)
SHELL=/bin/zsh
Another way to exercise this behaviour is this
perl 3>/dev/null -MIO::Handle -e 'open X, "<&3" or die $!; $_ = <X>; printf "%s %s\n", X->error(), $!;'
I looked through /dev and on my system this demonstrtes the malfuntion too:
perl -MIO::Handle -e 'open X, "/dev/video0" or die $!; $_ = <X>; printf "%s %s\n", X->error(), $!;'
(IHNI what /dev/video0 is; it came up near the end of my ls and I observed that cat </dev/video0 >/dev/null was able to open the file but not read it.)
In Debian 1016369, Damyan Ivanov provided this test program (which I've renamed with the two bug report numbers):
$ cat gh-12782-debian-1016369-io-handle.t
use Test::More;
plan skip_all => "IO::Handle not available" unless eval 'use IO::Handle; 1';
open(X, "<", ".") or die $!;
ok(!defined(<X>), 'failed reading from ".", as expected');
ok(X->error, 'X->error is TRUE after reading from "."');
close X;
SKIP: {
skip "/dev/full not available", 3 unless -w '/dev/full';
open X, '>', '/dev/full' or die $!;
ok((print X "1"), "successful write to /dev/full");
ok(!X->flush, "flush after writing to /dev/full fails");
ok(X->error, "X->error is TRUE after flushing /dev/full");
close X;
}
done_testing;
The program fails, but in different ways, on both Linux and FreeBSD.
Linux (Ubuntu 20.04 LTS)
$ prove -v gh-12782-debian-1016369-io-handle.t
gh-12782-debian-1016369-io-handle.t ..
ok 1 - failed reading from ".", as expected
not ok 2 - X->error is TRUE after reading from "."
# Failed test 'X->error is TRUE after reading from "."'
# at gh-12782-debian-1016369-io-handle.t line 7.
ok 3 - successful write to /dev/full
ok 4 - flush after writing to /dev/full fails
ok 5 - X->error is TRUE after flushing /dev/full
1..5
# Looks like you failed 1 test of 5.
Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/5 subtests
Test Summary Report
-------------------
gh-12782-debian-1016369-io-handle.t (Wstat: 256 (exited 1) Tests: 5 Failed: 1)
Failed test: 2
Non-zero exit status: 1
Files=1, Tests=5, 0 wallclock secs ( 0.04 usr 0.02 sys + 0.05 cusr 0.00 csys = 0.11 CPU)
Result: FAIL
FreeBSD (version 12)
$ prove -v gh-12782-debian-1016369-io-handle.t
gh-12782-debian-1016369-io-handle.t ..
ok 1 - failed reading from ".", as expected
not ok 2 - X->error is TRUE after reading from "."
# Failed test 'X->error is TRUE after reading from "."'
# at gh-12782-debian-1016369-io-handle.t line 7.
ok 3 - successful write to /dev/full
ok 4 - flush after writing to /dev/full fails
not ok 5 - X->error is TRUE after flushing /dev/full
# Failed test 'X->error is TRUE after flushing /dev/full'
# at gh-12782-debian-1016369-io-handle.t line 16.
1..5
# Looks like you failed 2 tests of 5.
Dubious, test returned 2 (wstat 512, 0x200)
Failed 2/5 subtests
Test Summary Report
-------------------
gh-12782-debian-1016369-io-handle.t (Wstat: 512 Tests: 5 Failed: 2)
Failed tests: 2, 5
Non-zero exit status: 2
Files=1, Tests=5, 0 wallclock secs ( 0.03 usr 0.01 sys + 0.10 cusr 0.00 csys = 0.14 CPU)
Result: FAIL
So our definition of the problem, as well as our solution and the tests we use to verify that solution, will have an OS-specific component.
The program fails, but in different ways, on both Linux and FreeBSD.
Linux (Ubuntu 20.04 LTS)
And, FWIW, it fails differently with different versions of Perl. On perl-5.32 and earlier, on Linux I get test failures in tests 2 and 5 just as I do on FreeBSD. On perl-5.34 I only get a failure in test 5. Bisecting points to the following commit as causing the improvement.
commit 89341f87f9fc65c4d7133e497bb04586e86b8052
Author: Tony Cook <[email protected]>
Date: Tue May 12 10:29:17 2020 +1000
make $fh->error report errors from both input and output
For character devices and sockets perl uses separate PerlIO objects
for input and output so they can be buffered separately.
The IO::Handle::error() method only checked the input stream, so
if a write error occurs error() would still returned false.
Change this so both the input and output streams are checked.
fixes #6799
I don't yet understand exactly how this relates to the OP's problem.
@tonycoz, @ppisar: You have recently touched ferror in dist/IO/IO.xs. Could you please take a look at this ticket?
I don't yet understand exactly how this relates to the OP's problem.
The referenced Debian report discusses both a read error issue and a write error issue.
The /dev/full test is for the write error issue. I believe it was #6799 and got fixed in 5.34.
The read error issue is what I filed this bug about.
Hope this clarifies.
I see #12782 is very similar but hasn't really received much attention. Is this something that should at least be documented as a caveat if it's not fixable?
I expect it's fixable, but might cause other changes in behaviour, I tried:
diff --git a/pp_hot.c b/pp_hot.c
index 08ddf9d7f6..31e008fb5a 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -3292,11 +3292,12 @@ Perl_do_readline(pTHX)
|| SNARF_EOF(gimme, PL_rs, io, sv)
|| PerlIO_error(fp)))
{
- PerlIO_clearerr(fp);
if (IoFLAGS(io) & IOf_ARGV) {
fp = nextargv(PL_last_in_gv, PL_op->op_flags & OPf_SPECIAL);
- if (fp)
+ if (fp) {
+ PerlIO_clearerr(fp);
continue;
+ }
(void)do_close(PL_last_in_gv, FALSE);
}
else if (type == OP_GLOB) {
which allowed one of your test cases to pass (I didn't try the others):
$ ./perl -Ilib -MIO::Handle -e 'open X, "<", "." or die $!; $_ = <X>; printf "%s %s\n", X->error(), $!;'
1 Is a directory
but caused a test failure I don't have time to track down right now.
