# cache
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Support for server-side caching in [Angel](https://angel-dart.github.io).

## `CacheService`
*TODO: Documentation*

A `Service` class that caches data from one service, storing it in another.
An imaginable use case is storing results from MongoDB or another database in
MemcacheD/Redis.

## `ResponseCache`
A flexible response cache for Angel.

Use this to improve real and perceived response of Web applications,
as well as to memoize expensive responses.

Supports the `If-Modified-Since` header, as well as storing the contents of
response buffers in memory.

To initialize a simple cache:

```dart
Future configureServer(Angel app) async {
  // Simple instance.
  var cache = new ResponseCache();
  
  // You can also pass an invalidation timeout.
  var cache = new ResponseCache(timeout: const Duration(days: 2));
  
  // Close the cache when the application closes.
  app.shutdownHooks.add((_) => cache.close());
  
  // Use `patterns` to specify which resources should be cached.
  cache.patterns.addAll([
    'robots.txt',
    new RegExp(r'\.(png|jpg|gif|txt)$'),
    new Glob('public/**/*'),
  ]);
  
  // REQUIRED: The middleware that serves cached responses
  app.use(cache.handleRequest);
  
  // REQUIRED: The response finalizer that saves responses to the cache
  app.responseFinalizers.add(cache.responseFinalizer);
}
```

### Purging the Cache
Call `invalidate` to remove a resource from a `ResponseCache`.

Some servers expect a reverse proxy or caching layer to support `PURGE` requests.
If this is your case, make sure to include some sort of validation (maybe IP-based)
to ensure no arbitrary attacker can hack your cache:

```dart
Future configureServer(Angel app) async {
  app.addRoute('PURGE', '*', (req, res) {
    if (req.ip != '127.0.0.1')
      throw new AngelHttpException.forbidden();
    return cache.purge(req.uri.path);
  });
}
```