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cgi download and delete file

by teddyttas (Novice)
on Aug 15, 2013 at 09:19 UTC ( #1049533=perlquestion: print w/replies, xml ) Need Help??
teddyttas has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks!

I would like to have your advice on the following problem:

I am making a small webapp and my purpose is to create a number of text files, compress them, download as zip file and erase.

For the moment I've been able to create the directory with the file, put them in a zip file and to download, but I can't erase the zip file. Well..It's not totally true. The problem is that if I do it, it compromises the download. My question would then be : Ho can I postpone the file elimination or, how can I check that the file has been totally completed before I erase it?

I know about the existence of File::Temp, but as I need this zip file just once, I think it would be simpler to just delete it. Here is a part of the code

sub write_and_download{ [...] $self->generate_zip(); $self->download_file(); my $filename = "temporary/" . $projectname . ".zip"; unlink $filename; }; sub download_file{ my $self = shift; my $downloadfile = $projectname . ".zip"; my $fullpathdownloadfile = "temporary/$downloadfile"; my $output = ''; my $buffer = ''; open my $fh, '<', $fullpathdownloadfile or return error_handler("Error: Failed to download file <b>$down +loadfile</b>:<br>$!<br>"); while (my $bytesread = read($fh, $buffer, 1024)) { $output .= $buffer; } close $fh or return error_handler("Error: Failed to download file <b>$down +loadfile<b>:<br>$!<br>"); my $downloadfilesize = (stat($fullpathdownloadfile))[7] or return error_handler("Error: Failed to get file size for <b>$ +downloadfile<b>:<br>$!<br>"); $self->header_props( '-type' => 'application/x-downl +oad', '-content-disposition' => "attachment;filename +=$downloadfile", '-content_length' => $downloadfilesize, ); return $output; };

I thank you from now for your help

Replies are listed 'Best First'.
Re: cgi download and delete file
by poj (Monsignor) on Aug 15, 2013 at 10:26 UTC
    You could create the zip 'on-the-fly' so no file to delete
    #!perl use strict; use Archive::Zip; use CGI qw(:standard); my $zip = Archive::Zip->new(); $zip->addFile('c:/temp/inet/test.pdf','test.pdf'); print header(-type=>'application/zip',-attachment=>''); binmode(STDOUT); $zip->writeToFileHandle(*STDOUT);
Re: cgi download and delete file
by flexvault (Monsignor) on Aug 15, 2013 at 10:11 UTC


    I have to guess that another script is going to use the zip file you create, since you don't call a subroutine or use the zip file in any way. A couple things can be done:

    • Let the other script delete the zip file.
    • Delete old zip files when creating new zip files. (see 'stat')
    • Call the other script before doing the 'unlink'.
    • Use 'sleep' to wait to do the 'unlink'.
    • etc. etc. etc.
    I think this comes down to "you know what you want to do", but we don't. Maybe a description of the timing consideration would help give you a better answer.


    "Well done is better than well said." - Benjamin Franklin

Re: cgi download and delete file
by sundialsvc4 (Abbot) on Aug 15, 2013 at 12:37 UTC

    You know that Private SNAFU is always on duty:   the mere fact that you zipped-up a bunch of files and pushed them to an HTML stream doesn’t mean that they arrived, any more than it does at the Post Office.   I would therefore design this program to build the Zip files, then remove the files from whence they were made (if appropriate), then put that file into a “to be downloaded” directory under some appropriate name.   From these, when the user requests a download, the file is renamed in some slight way to indicate that it “has been or is-being downloaded.”   (Renaming ahead-of-time avoids any file contention issues.   Moving it to a different directory ahead-of-time does the same thing.)   But in every step you have thus given yourself a way out.   If the download did not for whatever reason succeed, the data is still there and the process could be repeated.

      Thank you very much! Anyway, I think there is something I am getting wrong... When I use the cgi::application's header_prop (in the download_file subroutine) what I'm actually doing is a redirection to the download window, is it right? Cause I tried to make a redirection after the execution of the subroutine, but in this case the download doesn't start. If I put a sleep command after the subroutine, the script executes before the sleep command and then launches the download. So...I don't really understand this behaviour. I tried :
      $self->download_zip(); sleep 5; my $filename = "temporaneo/" . $self->session->param("nom_projet") + . ".zip"; unlink $filename;
      $self->generate_zip(); $self->download_zip(); return $self->redirect("http://delete.cgi");
      What I was trying to do was following your advice: put the zip file in another directory and, if succeed, redirect to another run mode that erases the file, otherwise stay on the page and relaunch the download.
        Okay, I think I got the solution to my last question... it was simple. In fact I solved it in the following way...
        $self->generate_zip(); my $output = $self->download_zip(); #here I can do what I want. unlink and so on.. my $filename = "temporaneo/" . $self->session->param("nom_projet") + . ".zip"; unlink $filename; #and only then I stream the output return $output;
        I can now redirect to another runmode passing the $output variable and solve the problem as you suggested. thank you very much!
Re: cgi download and delete file
by Anonymous Monk on Aug 15, 2013 at 11:49 UTC
    If you're using a variant of Unix for the web server, you can delete the file as soon as the download is initiated. The OS won't fully delete the file as long as a process has it open. (Of course, resuming the download will not work.)

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