Remove Extra bytes at end of file

slloyd has asked for the wisdom of the Perl Monks concerning the following question:

I am using CGI to accept an upload from windows machine and write a cab file on my linux server. I then try to use cabextract to open the saved cab file but it says that the uploaded cab file has "2 Extra bytes at end of file". Does anyone have a script to remove extra bytes at end of a file? or does anyone know how to solve this problem?

#!/usr/bin/perl
#use strict;
use CGI qw/:standard/;
use Digest::MD5 qw(md5 md5_hex md5_base64);
print header();
my $file = param('file');
if (!$file) {
    #file does not exist
     print "Error: No file to upload";
     return;
    }
#Ignore all but cab files
my $fname=$file;
if($fname !~/\.cab$/is){
    print "Error: Not a cab file";
    return;
    }
my $time=time();
my $data='';
while (<$file>) {
     $data .= $_;
    }
my $md5=md5_hex($data);
my $filename="ufiles/$md5\_" . $fname;
if(open(FH,">$filename")){
    binmode(FH);
    print FH $data;
    close(FH);
    #print the MD5 hash as a return value on success
    print $md5;
    }
else{
    print "Failed to upload file";
    }
[download]

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Comment on Remove Extra bytes at end of file Download Code

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Re: Remove Extra bytes at end of file by wojtyk (Friar) on Sep 08, 2006 at 15:41 UTC
My best guess is that the extra bytes could be the windows line feeds (\r\n). Did you try running dos2unix on the file first? Is the cab file a plain text file? Anyways, if you want to remove the characters manually, you could just use Tie::File and then `chop($tied_file[-1])` twice. Or slurp the thing into a scalar, chop twice, and then dump it back out to file.	[reply] [d/l]
Re: Remove Extra bytes at end of file by jdtoronto (Prior) on Sep 08, 2006 at 15:55 UTC
I would first use a binary editor to look at exactly what the two bytes are. Then you can figure out how/why they got added. jdtoronto	[reply]
Re: Remove Extra bytes at end of file by ikegami (Patriarch) on Sep 08, 2006 at 17:49 UTC
Possibly unrelated, but while you set your output to binmode, you didn't do the same for your input. Also, reading a binary file a "line" at a time makes no sense. Change `my $data=''; while (<$file>) { $data .= $_; }` [download] to `binmode($file); my $data; { local $/; $data = <$file>; }` [download]	[reply] [d/l] [select]
Re: Remove Extra bytes at end of file by BrowserUk (Patriarch) on Sep 08, 2006 at 17:19 UTC
If it is consistantly 2 bytes, and the program works if you remove them, then use truncate. If you know how long the file is, use it on the filehandle before you close it. If not, `truncate $filename, -s( $filename ) - 2;` after you've closed the filehandle might do the trick. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal? "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]