How to upload asset element on its own, not into an asset field (frontend form)

Question

I have read this resource about uploading a file to an asset field on an entry, but I believe I need to create the asset on its own because the asset has 2 custom fields associated with it that I want to define upon its creation. Is there not something like an 'assets/save-asset' action I can use to save an asset element without having to attach it to an entry?

Update: With Marion's help I'm a little closer. Side note: apparently 'assets/save-asset' is now depreciated in favor of 'assets/upload' so I'm using that. Here is my form:

              <form method='post' accept-charset='UTF-8' enctype='multipart/form-data'>
                {{ csrfInput() }}
                {{ actionInput('assets/upload') }}
                {{ hiddenInput('folderId', 7) }}
                {{ hiddenInput('title', 'cool image')}}
                <input name='file' type='file'>
                <input type='submit' value='submit'>
              </form>

But I am now getting a 400 Bad Request error with the message No file was uploaded. What am I doing wrong to not have my file attach correctly?

Answer 1

There is indeed an assets/save-asset controller. You will find it in vendor/craftcms/cms/src/controllers/AssetsController.php, the actionSaveAsset() function.

Answer 2

For anyone interested, I figured out that I had to name the asset field as "assets-upload" in order for it to work. I found this out by inspecting the asset upload button in the CP. Here is my working form code:

          <form method='post' accept-charset='UTF-8' enctype='multipart/form-data'>
            {{ csrfInput() }}
            {{ actionInput('assets/upload') }}
            {{ hiddenInput('folderId', 7) }}
            {{ hiddenInput('title', 'cool image')}}
            <input name="assets-upload" type='file'>
            <input type='submit' value='submit'>
          </form>

And remember, you can get your intended folderId also by inspecting the volume folders in the CP to see what the ID is.