Question

I have a perl -cgi script in which I need to test something based on when cgi_error() happens. Could some one please let me know under what scenario cgi_error() function gets invoked. I tried below

1. changed owner and permissions on the script

But that has not helped so far.

This is code snippet

use CGI qw(-compile :standard);
.....

 if (cgi_error()) {
...
}

It would be great if some one can explain when cgi_error() is invoked automatically in the script.

Answer 1

The cgi_error is not called “automatically”. However, depending on the circumstances, it will return information to see if something went wrong.

From the CGI documentation:

RETRIEVING CGI ERRORS

Errors can occur while processing user input, particularly when processing uploaded files. When these errors occur, CGI will stop processing and return an empty parameter list. You can test for the existence and nature of errors using the cgi_error() function. The error messages are formatted as HTTP status codes. You can either incorporate the error text into an HTML page, or use it as the value of the HTTP status:

my $error = $q->cgi_error;
  if ($error) {
    print $q->header(-status=>$error),
    $q->start_html('Problems'),
    $q->h2('Request not processed'),
    $q->strong($error);
    exit 0;
  }

When using the function-oriented interface (see the next section), errors may only occur the first time you call param(). Be ready for this!

and

Handling interrupted file uploads

There are occasionally problems involving parsing the uploaded file. This usually happens when the user presses “Stop” before the upload is finished. In this case, CGI.pm will return undef for the name of the uploaded file and set cgi_error() to the string “400 Bad request (malformed multipart POST)”. This error message is designed so that you can incorporate it into a status code to be sent to the browser. Example:

$file = $q->upload('uploaded_file');
  if (!$file && $q->cgi_error) {
    print $q->header(-status=>$q->cgi_error);
    exit 0;
  }

and

An attempt to send a POST larger than $POST_MAX bytes will cause param() to return an empty CGI parameter list. You can test for this event by checking cgi_error(), either after you create the CGI object or, if you are using the function-oriented interface, call param() for the first time. If the POST was intercepted, then cgi_error() will return the message “413 POST too large”.