404 Error from WordPress Form Submit with an input named 'name'

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Form with name="name" causes 404 in WordPress

While I haven't tracked down the source of the problem within WordPress itself, I was having some trouble with a form on a custom template on a WordPress site.

I had made my form, was hitting submit then promptly seeing a 404 page.

Confusing? I'll say, especially considering the form was submitting to itself. So I took a look at my code, commented out the redirects I had, through error_log around a little trying to track down where the execution broke. Nothing. No err's, no warnings.

So I did what any developer does, I googled a few keywords checking for 404 errors on submitting a form, and then eventually ended up on this support forum where member ianstapleton noted that changing the input name caused the form submission to work again.

It's a bit of a strange fix, but it makes sense when you consider the code inside of Wordpress Core. Here's the snippet that is causing the slightly unexpected behavior:

wp-includes/query.php (WordPress Version 3.7.1)
2337        if ( '' != $q['name'] ) {
2338            $q['name'] = sanitize_title_for_query( $q['name'] );
2339            $where .= " AND $wpdb->posts.post_name = '" . $q['name'] . "'";
2340        } elseif ( '' != $q['pagename'] ) {
2341            if ( isset($this->queried_object_id) ) {

The $q variable is the query variables which are retrieved like this:

wp-includes/class-wp.php (WordPress Version 3.7.1)
2142        $q = &$this->query_vars;
2143
2144        // Fill again in case pre_get_posts unset some vars.
2145        $q = $this->fill_query_vars($q);

In other words, the $_POST and $_GET variables seem to be merged into a single query_vars propertie and then used from there. wp_parse_args is used during part of the merging (from a brief look into the fill_query_vars function) and so we end up looking for a post with the name of whatever we submitted in the form. Which is, not what we wanted to do. You could use it to create a custom search form for looking for exact matches on post names, but that'd be a little silly.

Regardless, I wonder if this is the intended behavior of WordPress or just a result of lots of code making the assumptions that no user will ever try to use

<input type="text" name="name" />

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