[Catalyst] TIP: When file uploads just don't work, try multipart/form-data!

In the hopes of sparing another unfortunate soul from suffering the
wrestling match I've been having this week...


SYMPTOM: Regardless of how many upload-file fields you have in your form,
Catalyst doesn't see the file uploads. That is, *$c->req->uploads* is an
empty hash?! And *$c->req->upload* is an empty array?! File uploads are not
working at all!

Let's say you develop a form that works just fine, and then you add an
upload field. Everything else still works as before, but the uploads are
ignored: *$c->req->uploads* is an empty hash (and *$c->req->upload* is an
empty array). You can see some of the details in *$c->req->_body* but
there's no uploaded info to work with! You can't get the uploaded file from
/tmp/blahblahblah because there isn't any such uploaded file. You can't see
the size or the content or the mime-type. It's as if nothing is uploaded at
all.


SOLUTION: To deal with uploaded files, your form must use "*
multipart/form-data*"! It's not Catalyst's fault, your web browser behaves
differently depending on the <form> attributes you specified. Here's the
primary snippet to add when using HTML::FormHandler...

{
package MyApp::Form::UploadForm;
use HTML::FormHandler::Moose;
extends 'HTML::FormHandler::Model::DBIC';
with 'HTML::FormHandler::Render::Table';

has '+item_class' => ( default => 'RecordSpecHere' );

# MULTIPART/FORM-DATA is MANDATORY for file-uploads, beware!
* has '+enctype' => ( default => 'multipart/form-data' );*

has_field 'id' => ( type => 'Hidden', );
#...
has_field 'myfile' => ( type => 'Upload' );
}


At any rate, your form tag will now look a bit like this:

<form enctype="*multipart/form-data*" method="*post*" id="form996">

Single-stepping through the Perl debugger will now show that Catalyst has
everything you need in *$c->req->uploads*:

DB<3> *x $c->req->uploads*
0 HASH(0xc54f598)
'myfile' => Catalyst::Request::Upload=HASH(0xc56d858)
'filename' => 'sample-file.txt'
'headers' => HTTP::Headers=HASH(0xc56d918)
'content-disposition' => 'form-data; name="myfile";
filename="sample-file.txt"'
'content-type' => 'application/octet-stream'
'size' => 74
'tempname' => '/tmp/BqoVhCmj3f'
'type' => 'text/plain'

Woo hoo!