@skazka/server-cors/README.md

Server cors

# Server cors

Skazka Server Cross-Origin Resource Sharing (CORS).

[![NPM](https://nodei.co/npm/@skazka/server-cors.png)](https://npmjs.org/package/@skazka/server-cors)

## How to install

    npm i @skazka/server @skazka/server-cors
    
With yarn:

    yarn add @skazka/server @skazka/server-cors
    
Optionally you can add http server, error handler, logger, router, request and response:

    npm i @skazka/server-http @skazka/server-router @skazka/server-error @skazka/server-logger @skazka/server-request @skazka/server-response
      
With yarn:

    yarn add @skazka/server-http @skazka/server-router @skazka/server-error @skazka/server-logger @skazka/server-request @skazka/server-response

## How to use

### Server module

```javascript
const App = require('@skazka/server');
const Router = require('@skazka/server-router');
        
const cors = require('@skazka/server-cors');
        
const error = require('@skazka/server-error');
const logger = require('@skazka/server-logger');

const request = require('@skazka/server-request');
const response = require('@skazka/server-response');
        
const server = require('@skazka/server-http');
        
const app = new App();
const router = new Router();
        
app.all([
  error(),
  logger(),
  request(),
  cors(),
  response(),
]);
    
router.get('/data').then(async (ctx) => {
  return ctx.response('data'); 
});
        
app.then(router.resolve());
        
server.createHttpServer(app);
```

## Configuring CORS

```javascript
const corsOptions = {
  origin: 'http://example.com',
  optionsSuccessStatus: 200 // some legacy browsers (IE11, various SmartTVs) choke on 204
}

app.then(cors(corsOptions)); //This is CORS-enabled for only example.com.
```

If you do not want to block REST tools or server-to-server requests,
add a `!origin` check in the origin function like so:

```javascript
var corsOptions = {
  origin(origin, callback) {
    if (whitelist.indexOf(origin) !== -1 || !origin) {
      callback(null, true)
    } else {
      callback(new Error('Not allowed by CORS'))
    }
  }
}
```

### Enabling CORS Pre-Flight

```javascript
const app = new App();
app.all([
  error(),
  logger(),
  response(),
]);
    
router.get('/data').then(async (ctx) => {
  await cors();
  return ctx.response('data'); 
});
        
app.then(router.resolve());
        
server.createHttpServer(app);
```

## Configuration Options

* `origin`: Configures the **Access-Control-Allow-Origin** CORS header. Possible values:
  - `Boolean` - set `origin` to `true` to reflect the [request origin](http://tools.ietf.org/html/draft-abarth-origin-09), as defined by `req.header('Origin')`, or set it to `false` to disable CORS.
  - `String` - set `origin` to a specific origin. For example if you set it to `"http://example.com"` only requests from "http://example.com" will be allowed.
  - `RegExp` - set `origin` to a regular expression pattern which will be used to test the request origin. If it's a match, the request origin will be reflected. For example the pattern `/example\.com$/` will reflect any request that is coming from an origin ending with "example.com".
  - `Array` - set `origin` to an array of valid origins. Each origin can be a `String` or a `RegExp`. For example `["http://example1.com", /\.example2\.com$/]` will accept any request from "http://example1.com" or from a subdomain of "example2.com".
  - `Function` - set `origin` to a function implementing some custom logic. The function takes the request origin as the first parameter and a callback (which expects the signature `err [object], allow [bool]`) as the second.
* `methods`: Configures the **Access-Control-Allow-Methods** CORS header. Expects a comma-delimited string (ex: 'GET,PUT,POST') or an array (ex: `['GET', 'PUT', 'POST']`).
* `allowedHeaders`: Configures the **Access-Control-Allow-Headers** CORS header. Expects a comma-delimited string (ex: 'Content-Type,Authorization') or an array (ex: `['Content-Type', 'Authorization']`). If not specified, defaults to reflecting the headers specified in the request's **Access-Control-Request-Headers** header.
* `exposedHeaders`: Configures the **Access-Control-Expose-Headers** CORS header. Expects a comma-delimited string (ex: 'Content-Range,X-Content-Range') or an array (ex: `['Content-Range', 'X-Content-Range']`). If not specified, no custom headers are exposed.
* `credentials`: Configures the **Access-Control-Allow-Credentials** CORS header. Set to `true` to pass the header, otherwise it is omitted.
* `maxAge`: Configures the **Access-Control-Max-Age** CORS header. Set to an integer to pass the header, otherwise it is omitted.
* `preflightContinue`: Pass the CORS preflight response to the next handler.
* `optionsSuccessStatus`: Provides a status code to use for successful `OPTIONS` requests, since some legacy browsers (IE11, various SmartTVs) choke on `204`.

The default configuration is the equivalent of:

```json
{
  "origin": "*",
  "methods": "GET,HEAD,PUT,PATCH,POST,DELETE",
  "preflightContinue": false,
  "optionsSuccessStatus": 204
}
```

For details on the effect of each CORS header, read [this](http://www.html5rocks.com/en/tutorials/cors/) article on HTML5 Rocks.