Proposed improvement to handling of file input

[djyotta]

Currently, when a file input is present, the default validation (submit) button has formenctype="multipart/form-data" set on it.

This is to ensure that file uploads work without requiring the developer to set he enctype on the form element.

The drawback with doing it this way, is the following won't work as expected:

Multiple submit buttons

SELECT 'form' AS component;
SELECT 'file' AS type, 'data' AS name, '' AS label;
-- the default submit button will work, but this custom submit button won't.
SELECT 'submit' AS type, 'Alternative Submit' AS value, '/other-backend.sql' AS formaction;

External submit buttons

SELECT 'form' AS component, '' AS validate, 'upload' AS id;
SELECT 'file' AS type, 'data' AS name, '' AS label;
-- external buttons don't work
SELECT 'button' AS component, 'upload' AS form;

Overrides form enctype if set

SELECT 'form' AS component
, 'upload' AS id
-- oops! default validate button overrides the form enctype
, 'application/x-www-form-urlencoded' AS enctype;
SELECT 'file' AS type, 'data' AS name, '' AS label;
-- can work around with a custom button
SELECT 'submit' AS type, 'Submit as urlencoded' AS value, 'application/x-www-form-urlencoded'  AS formenctype;
-- or an external button
SELECT 'button' AS component, 'upload' AS form;

So my proposal is to set the enctype of the form to multipart/form-data by default.

This means that form will submit successfully regardless of default validate (submit) button or custom submit buttons or even external submit buttons.

One obvious issue with multipart/form-data as default it that even simple text values in forms will be posted as multipart form data, which will be a significant increase to the payload if there are many form fields with short text values.

To work around this, I propose adding formenctype="application/x-www-form-urlencoded" to the default submit button only if the form enctype is not set.
This would preserve the existing behaviour for users who don't modify form encoding whilst fixing the fact that any custom or external submit buttons currently do not work without setting the encoding type.

Power users can then set the form enctype and/or input formenctype precisely as required, without the auto-magic feature overriding explicitly set values.