Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl: the Markov chain saw

Re: Code review, good 'ol CGI.

by tachyon (Chancellor)
on Jul 29, 2001 at 11:26 UTC ( #100653=note: print w/replies, xml ) Need Help??

in reply to Code review, good 'ol CGI.

A few points. When locking a file I use this little snippet to allow a script to wait for its lock:

my $flock = 1; # set to true to flock my $timeout = 10; # set to number of seconds before flock timeout .... if ($flock) { my $count = 0; until (flock FILE, LOCK_SH) { sleep 1; DieNice("Can't lock file '$file': $!\n") if ++$count >= $timeout +; } }

Also closing a filehandle removes the underlying file lock so you only need to close them, Perl will unlock them for you thus all the LOCK_UN lines are redundant.

This line does nothing useful, it does not untaint $mode

$mode =~ tr#a-z_##cd; # untaint that param!

This bit uses $mode in a regex and the value in $1 assigned to $page is untainted.

if ( $mode =~ /^([a-z_]+)_go$/ ) { $page = $1 or die "no page given!";

The or die makes no logical sense as the assignment $page = $1 will always succeed thus this can never execute.

You have a number of or die "blah" statements. You should include the $! special var as this stores Perl's explanation of the error that has triggered the die ie "File does not exist". The standard synatax goes like:

open FILE, ">>$file" or die "Can't append to $file, Perl says $!\n";

This code is a very obtuse way to do something quite simple, namely go to one of two subs depending on the user input.

sub main { my %dispatch = ( upload => \&upload, debug => \&debug, DEFAULT => \&upload, ); $draw->headers(); $draw->html_start( { title => $title } ); my $action = $cgi->param('action') || 'DEFAULT'; my $do_sub = $dispatch{ $action }; if ( $do_sub ) { &$do_sub(); } else { warn "[warn] Invalid action: [$action]"; die "[die] You can't make me do that!\n"; } $draw->html_end(); }

You create a hash of sub references and then eventually call them. This is much easier to follow:

sub main { $draw->headers(); $draw->html_start( { title => $title } ); if ($cgi->param('action') eq 'debug'){ &debug; } else { &upload; } $draw->html_end(); }

The logic is the same with the exception of not checking for 'incorrect' action params. This is the typical logic I use as it is simple - either you ask for something with the correct name or you get the default page. The use of warn and die as you do is also redundant. Both warn and die print to STDERR. Warn just does this whereas die throws an expception afterwards. Logically you are just doing a die here.

Your open files in two different places in the script then lock them all in the one place. This makes no logical sense to me and makes it hard to follow your logic train.

Finally in CGI die is oftem suboptimal. You should not run a production script with use CGI::Carp qw( fatalsToBrowser ) active as it makes it easier to hack a script as the exact errors are reported in the browser. Without carp die will give the user a 500 error when it gets called. For these reasons amongst others most developers write a die_nice routine. Here is a die_nice routine:

sub DieNice { my $message = shift; my ($package, $file, $line) = caller(); my $user_message = "Sorry, the system is currently unable to proce +ss your request<br>\n"; $user_message .= "due to routine maintenance. Please try again lat +er. Our Apologies\n"; $message = Unindent <<" MESSAGE"; A fatal die was trapped by the $scriptname die nice routine, detai +ls: Time: $datetime List name: $list_name Script name: $scriptname Package: $package File: $file Line Number: $line Error Message: $message MESSAGE &TellUser($user_message); # the bullshit message! &WarnAdmin($message); # the real facts! exit; } sub WarnAdmin { my $message = shift; my $name = "Administrator"; my $email = $our_email; &EmailUser ($name, $email, $message); return; } sub Unindent { my $unindent = shift; $unindent =~ s/^[ \t]+//gm; return $unindent; }

The unindent sub just lets me indent the herepage stuff with the sub and drop this indentation off the final output. Hope this helps, all up looks good with -Tw, use strict, setting a secure path etc.




Replies are listed 'Best First'.
Re: Re: Code review, good 'ol CGI.
by meonkeys (Chaplain) on Jul 30, 2001 at 05:05 UTC
    First of all, I just want to say thank you for the excellent comments you offered. I've coded Perl for about a year now, but within Text::Forge I'm shielded from most of the issues involved in traditional CGI programming, hence my immature code. I ignored some of your suggestions because I'm lazy.

    This line does nothing useful, it does not untaint $mode
    tr/// can't be used to untaint? I didn't know that.

    This code is a very obtuse way to do something quite simple, namely go to one of two subs depending on the user input.
    Quite true. This is just my "cookie cutter" dispatch hash... it makes more sense in a CGI that has many functions; although a CGI with many functions probably doesn't make much sense...

    The main thing I've changed below is file locking. Could you take a look at this and tell me what you think? I'm attempting to use semaphores as advised by KM in a few of his/her posts.

    I like the following and will definitely use them in my next CGI:
    1. waiting for lock sleeper 2. your DieNice, WarnAdmin, and Unindent routines
    #!/usr/local/bin/perl -Tw # Pre-live checklist: # [X] add some file locking for Godsakes!!! # [X] link to this thing and do auth ONLY through SSL!! # [X] protect /admin dir with .htaccess # [X] use $ENV{ REMOTE_USER } once .htaccess is in place # [X] make sure to untaint $ENV{ REMOTE_USER } # [X] write a file-storing routine ... just did it inline instead # [X] bonus points: use XML :) # [X] app tempfiles? # [X] move to "live" data dir automatically? # [X] add CSV validation to _validate_upload # [X] test CSV validation to _validate_upload # [X] count fields in a cool way for $num_fields use lib '/dw02/d37/dawgpolo/myperl'; use lib '/dw02/d37/dawgpolo/myperl/lib'; use CGI; use CGI::Carp qw( fatalsToBrowser ); # I think this slows us down use Data::Dumper; use Date::Format; use Dawg qw( %CONFIG %CSV ); use Dawg::DB; use Dawg::Draw; use Fcntl qw( :flock ); use strict; $ENV{ HTTPS } or die "Insecure! Change URL to https://$ENV{ HTTP_HOST +}". "$ENV{ SCRIPT_NAME }\n"; $ENV{ HTTPS } =~ tr/A-Za-z//cd; $ENV{ SERVER_ADMIN } = $CONFIG{ EMAIL }; $ENV{ PATH } = '/usr/local/bin:/usr/bin:/bin'; my $cgi = CGI->new; my $draw = Dawg::Draw->new; my $title = 'CSV Update Tool'; my $self = $ENV{ SCRIPT_NAME }; my $user = $ENV{ REMOTE_USER }; $user =~ tr/A-Za-z//cd; my $userIP = $ENV{ REMOTE_ADDR }; sub main { my %dispatch = ( upload => \&upload, debug => \&debug, DEFAULT => \&upload, ); $draw->headers(); $draw->html_start( { title => $title } ); my $action = $cgi->param('action') || 'DEFAULT'; my $do_sub = $dispatch{ $action }; if ( $do_sub ) { &$do_sub(); } else { warn "[warn] Invalid action: [$action]"; die "[die] You can't make me do that!\n"; } $draw->html_end(); } sub upload { my @errors = (); # array of errors found during execution my @lines = (); # input lines of uploaded file my $page = ''; # page that uploaded file corresponds to my $ucpage = ''; # uppercased version of the same thang my $mode = $cgi->param( 'mode' ); $mode =~ tr#a-z_##cd; # untaint that pa +ram! my $in = $cgi->upload( 'datafile_in' ); # returns a fileh +andle my $logfile = "$CONFIG{ ADMIN }/transactions.log"; # log entire tran +saction my $qwiklog = "$CONFIG{ ADMIN }/quicklog.csv"; # abbreviated log open( LOG, ">> $logfile" ) or die "Couldn't open $logfile"; open( QWK, ">> $qwiklog" ) or die "Couldn't open $qwiklog"; if ( $mode ) { # They're trying to upload a file push @errors, "Invalid filename" unless ( ref $in eq 'Fh' ); # retrieve the uploaded file and check for data integrity unless ( @errors ) { my $rv = Dawg::DB->slurp_csv_safe( $in ); if ( $rv ) { @lines = @$rv; } else { die "No lines returned while slurping CSV"; } if ( $mode =~ /^([a-z_]+)_go$/ ) { $page = $1; $ucpage = uc($page); die "unknown page [$ucpage]" unless ( exists $CSV{$ucpage} ); my $result = Dawg::DB->validate_csv( $ucpage, \@lines ); @errors = @$result unless $result == 1; } } if ( @errors ) { print qq[ <FONT COLOR="RED">ERRORS OCCURRED DURING FILE UPLOAD:\ +n<BR> ]; print qq[ <UL>\n ]; foreach my $error ( @errors ) { print "<LI>$error\n"; } print qq[ </UL></FONT>\n ]; } else { # upload was good. my $time = time2str( "%C", time() ); my $outfile = "$CONFIG{DATA}/$page.csv" or die "cannot draft datafile filename for [$page]"; open( CSV, "> $outfile" ) or die "Couldn't open $outfile"; print qq[ <FONT COLOR="GREEN">$ucpage UPLOAD SUCCESSFUL</FONT><B +R>\n ]; # - 1 - open and lock semaphores my $csv_sem = "$CONFIG{ADMIN}/.csv.lock"; my $log_sem = "$CONFIG{ADMIN}/.transactions.lock"; my $qwk_sem = "$CONFIG{ADMIN}/.quicklog.lock"; open( CSV_SEM, "> $csv_sem" ) or die "$csv_sem: $!"; open( LOG_SEM, "> $log_sem" ) or die "$log_sem: $!"; open( QWK_SEM, "> $qwk_sem" ) or die "$qwk_sem: $!"; flock( CSV_SEM, LOCK_EX ) or die "Can't lock CSV"; flock( LOG_SEM, LOCK_EX ) or die "Can't lock LOG"; flock( QWK_SEM, LOCK_EX ) or die "Can't lock QWK"; # - 2 - write the datafile itself for (@lines) { print CSV "$_\n" } # write csv to datafile # - 3 - write the entire transaction print LOG "[ $time ] $ucpage UPDATED by $user [$userIP]\n"; for (@lines) { print LOG "$_\n" } # log the transaction # - 4 - write a "qwiklog" entry print QWK "[ $time ] $ucpage UPDATED by $user [$userIP]\n"; # - 5 - close all filehandles, drop locks close( CSV ) or die "Couldn't close file $outfile"; # file lock +s close( LOG ) or die "Couldn't close file $logfile"; # are remov +ed close( QWK ) or die "Couldn't close file $qwiklog"; # automatic +ally close( CSV_SEM ) or warn "close error on $csv_sem: $!"; close( LOG_SEM ) or warn "close error on $log_sem: $!"; close( QWK_SEM ) or warn "close error on $qwk_sem: $!"; } } else { # They're not trying to upload a file YET, so give them tips print <<End_HTML; Hints:<BR> <UL> <LI>Make sure the uploaded file is TRUE CSV, eg. blah,1,2,"blow, joe +" <LI>Click the respective Upload button once, then <EM>wait</EM> <LI>You can only upload one file at a time </UL> End_HTML } foreach my $table ( sort keys %CSV ) { my $name = lc($table); print <<UploadForms; <BR> Download <A HREF="$CONFIG{ WEBDATA }/$name.csv">$name</A> datafile <FORM ACTION="$self" METHOD="POST" ENCTYPE="multipart/form-data"> <INPUT TYPE="FILE" NAME="datafile_in" SIZE="50" MAXLENGTH="80"> <BR> <INPUT TYPE="SUBMIT" VALUE="Upload $name"> <INPUT TYPE="HIDDEN" NAME="mode" VALUE="${name}_go"> </FORM> <BR> UploadForms } } sub debug { print "<PRE>\n"; print Data::Dumper->Dump( [\%ENV], ['ENV'] ); print "</PRE>\n"; } main();

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://100653]
[atcroft]: abner: Or are you wanting to do something where you need to bind an array to a placeholder (in which case the bind_param_array method may be of use.
[abner]: Thanks I will try out your suggestion.

How do I use this? | Other CB clients
Other Users?
Others musing on the Monastery: (7)
As of 2017-01-24 04:06 GMT
Find Nodes?
    Voting Booth?
    Do you watch meteor showers?

    Results (202 votes). Check out past polls.