Issue #2939653 by richgerdes: Files missing when accessing Swagger UI JSON

## OpenAPI Docs Module Documentation

The  OpenAPI Docs (swagger_ui) module provides a visual web UI for browsing REST API documentation. It makes use of the [swagger-ui library](https://github.com/swagger-api/swagger-ui).

## OpenAPI Swagger UI Module Documentation

The  OpenAPI Swagger UI module provides a visual web UI for browsing REST API

documentation using [swagger-ui](https://github.com/swagger-api/swagger-ui).

The swagger-ui library needs to be installed into the drupal libraries folder

for this module to work properly. For sites using composer, the package is found

on Packagist. Otherwise installation can be done manually.

### Installation - Composer (recommended)

If you're using composer to manage the site (recommended), follow these steps:

If you're using composer to manage the site (recommended), there are two

composer plugins required for this setup, `composer/installers` and `mnsami/

composer-custom-directory-installer`. `composer-custom-directory-installer`

extends the base installer libraries to allow setting installer path for an

individual package. Follow the steps below.

1. Run `composer require --prefer-dist composer/installers` to ensure that you have the `composer/installers` package installed. This package facilitates the installation of packages into directories other than `/vendor` (e.g. `/libraries`) using Composer.

1. Run the following to ensure that you have the `composer/installers` and

`mnsami/composer-custom-directory-installer` packages installed. These package

facilitate the installation of packages into directories other than `/vendor`

(e.g. `web/libraries`) using Composer.

2. Add the following to the "repositories" section of your project's composer.json:

```

-drush en -y swagger_ui

{

  "type": "package",

  "package":{

    "name": "swagger-api/swagger-ui",

    "version": "3.0.17",

    "type": "drupal-library",

    "dist"    : {

      "url": "https://github.com/swagger-api/swagger-ui/archive/v3.0.17.zip",

      "type": "zip"

    },

    "require": {

        "composer/installers": "~1.0"

    }

  }

}

composer require composer/installers mnsami/composer-custom-directory-installer

```

3. Add the following to the "installer-paths" section of `composer.json`:

2. Edit your project's composer.json file to include instructions for installing

the `swagger-ui` library to Drupal's `/libraries`. Your file should include the

following:

```

"libraries/{$name}": ["type:drupal-library"],

"extra": {

  "installer-paths": {

    ...

    "web/libraries/{$name}": ["swagger-api/swagger-ui", "type:drupal-library"],

    ...

  }

}

```

4. Run the following to add the swagger-ui library to your composer.json and download it to /libraries:

3. Run the following to add the swagger-ui library to your composer project. It

will be automatically installed into `web/libraries`

```

composer require swagger-api/swagger-ui 3.0.17

```

*__NOTE:__ Using a version of `swagger-ui` other then 3.0.17, can cause issues

with the display of swagger-ui within your Drupal Site.*

### Installation - Manual

Extract https://github.com/swagger-api/swagger-ui/archive/v3.0.17.zip into /libraries/swagger-ui

If you are not managing your project through composer you can manually download

swagger-ui from https://github.com/swagger-api/swagger-ui/archive/v3.0.17.zip,

and extract the files into your `/libraries/swagger-ui` for your Drupal Project.