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Re: [perl #31455] Dup DATA filehandle, lose initial data

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From:
Nick Ing-Simmons
Date:
September 6, 2004 02:42
Subject:
Re: [perl #31455] Dup DATA filehandle, lose initial data
Message ID:
20040906094146.7181.2@llama.elixent.com
Jim Carter <perl5-porters@perl.org> writes:
># New Ticket Created by  Jim Carter 
># Please include the string:  [perl #31455]
># in the subject line of all future correspondence about this issue. 
># <URL: http://rt.perl.org:80/rt3/Ticket/Display.html?id=31455 >
>
>

Can you try this with 
PERLIO=perlio perl ...
and 
PERLIO=stdio perl ...
and see if it occurs in both cases?

Note that a dup'ed file handle shares the file pointer.
For DATA which perl is reading using buffered IO the
dup tries to do a seek to get fd level file pointer 
to match buffered point. Do you _need_ to do a dup ?

>
>This is a bug report for perl from jimc@math.ucla.edu,
>generated with the help of perlbug 1.34 running under perl v5.8.3.
>
>#!/usr/bin/perl 
># If the script is not seekable, and if the DATA filehandle is duped, an
># initial segment of the DATA is lost when reading from the duplicate
># handle. With this script the lossage is 4216 bytes from start of
># script or 2959 bytes from start of DATA.  In the production 
># script where this was discovered, the loss from start of DATA is in 
># the range 3500 to 4000 bytes.
>#    The production context is, we concatenate a "tripwire" type script
># and the filenames and checksums it should verify (customized per
># host), and do ssh remotehost "perl - -f '<&DATA'" where -f tells the
># script where to find the checksum list.  That way the hackers have
># little to attack -- only by munging perl itself can they defend
># themselves.
>print <<EOF;
>Compare these three command lines:
>    perl datatrunc.pl		# Seekable script, runs perfectly
>    perl - < datatrunc.pl	# Seekable script, runs perfectly
>    cat datatrunc.pl | perl -	# Not seekable, loses initial DATA
>EOF
>open(DUPL, "<&DATA") or die "Failed to dup DATA filehandle: $!\n";
>while (<DUPL>) {		# Each line is exactly 80 bytes including \n
>    print
>}
>__DATA__
>Line 01   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 02   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 03   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 04   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 05   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 06   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 07   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 08   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 09   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 10   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 11   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 12   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 13   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 14   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 15   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 16   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 17   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 18   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 19   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 20   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 21   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 22   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 23   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 24   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 25   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 26   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 27   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 28   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 29   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 30   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 31   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 32   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 33   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 34   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 35   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 36   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 37   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 38   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 39   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>Line 40   b123456789c123456789d123456789e123456789f123456789g123456789h12345678
>---
>Flags:
>    category=core
>    severity=medium
>---
>This perlbug was built using Perl v5.8.3 - Sat Apr  3 00:50:30 UTC 2004
>It is being executed now by  Perl v5.8.3 - Sat Apr  3 00:37:21 UTC 2004.
>
>Site configuration information for perl v5.8.3:
>
>Configured by abuild at Sat Apr  3 00:37:21 UTC 2004.
>
>Summary of my perl5 (revision 5.0 version 8 subversion 3) configuration:
>  Platform:
>    osname=linux, osvers=2.6.4, archname=i586-linux-thread-multi
>    uname='linux d209 2.6.4 #1 smp thu mar 11 17:56:49 utc 2004 i686 i686 i386 gnulinux '
>    config_args='-ds -e -Dprefix=/usr -Dvendorprefix=/usr -Dinstallusrbinperl -Dusethreads -Di_db -Di_dbm -Di_ndbm -Di_gdbm -Duseshrplib=true -Doptimize=-O2 -march=i586 -mcpu=i686 -fmessage-length=0 -Wall -Wall -pipe'
>    hint=recommended, useposix=true, d_sigaction=define
>    usethreads=define use5005threads=undef useithreads=define usemultiplicity=define
>    useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
>    use64bitint=undef use64bitall=undef uselongdouble=undef
>    usemymalloc=n, bincompat5005=undef
>  Compiler:
>    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -fno-strict-aliasing -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
>    optimize='-O2 -march=i586 -mcpu=i686 -fmessage-length=0 -Wall -Wall -pipe',
>    cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -fno-strict-aliasing'
>    ccversion='', gccversion='3.3.3 (SuSE Linux)', gccosandvers=''
>    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
>    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
>    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
>    alignbytes=4, prototype=define
>  Linker and Libraries:
>    ld='cc', ldflags =''
>    libpth=/lib /usr/lib /usr/local/lib
>    libs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
>    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
>    libc=, so=so, useshrplib=true, libperl=libperl.so
>    gnulibc_version='2.3.3'
>  Dynamic Linking:
>    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic -Wl,-rpath,/usr/lib/perl5/5.8.3/i586-linux-thread-multi/CORE'
>    cccdlflags='-fPIC', lddlflags='-shared'
>
>Locally applied patches:
>    
>
>---
>@INC for perl v5.8.3:
>    /usr/lib/perl5/5.8.3/i586-linux-thread-multi
>    /usr/lib/perl5/5.8.3
>    /usr/lib/perl5/site_perl/5.8.3/i586-linux-thread-multi
>    /usr/lib/perl5/site_perl/5.8.3
>    /usr/lib/perl5/site_perl
>    /usr/lib/perl5/vendor_perl/5.8.3/i586-linux-thread-multi
>    /usr/lib/perl5/vendor_perl/5.8.3
>    /usr/lib/perl5/vendor_perl
>    .
>
>---
>Environment for perl v5.8.3:
>    HOME=/home/jimc
>    LANG (unset)
>    LANGUAGE (unset)
>    LD_LIBRARY_PATH (unset)
>    LOGDIR (unset)
>    PATH=.:/home/jimc/bin:/usr/diklo/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/usr/X11R6/bin:/sbin:/bin:/usr/games:/opt/gnome/bin:/opt/kde3/bin:/sbin:/usr/sbin
>    PERL_BADLANG (unset)
>    SHELL=/bin/tcsh


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