Use sha1 to reduce the risk of collisions (#12)

* Use sha1 to reduce the risk of collisions

* Only cache if the max age is positive

* Updated tests

* Support setting a hash_algo

* CS

* Reverted accidental change

Author: GrahamCampbell

Diff for: spec/CachePluginSpec.php

@@ -42,7 +42,7 @@ function it_caches_responses(CacheItemPoolInterface $pool, CacheItemInterface $i
         $response->getHeader('Cache-Control')->willReturn(array());
         $response->getHeader('Expires')->willReturn(array());
 
-        $pool->getItem('e3b717d5883a45ef9493d009741f7c64')->shouldBeCalled()->willReturn($item);
+        $pool->getItem('d20f64acc6e70b6079845f2fe357732929550ae1')->shouldBeCalled()->willReturn($item);
         $item->isHit()->willReturn(false);
         $item->set(['response' => $response, 'body' => $httpBody])->willReturn($item)->shouldBeCalled();
         $item->expiresAfter(60)->willReturn($item)->shouldBeCalled();
@@ -63,7 +63,7 @@ function it_doesnt_store_failed_responses(CacheItemPoolInterface $pool, CacheIte
         $response->getHeader('Cache-Control')->willReturn(array());
         $response->getHeader('Expires')->willReturn(array());
 
-        $pool->getItem('e3b717d5883a45ef9493d009741f7c64')->shouldBeCalled()->willReturn($item);
+        $pool->getItem('d20f64acc6e70b6079845f2fe357732929550ae1')->shouldBeCalled()->willReturn($item);
         $item->isHit()->willReturn(false);
 
         $next = function (RequestInterface $request) use ($response) {
@@ -101,7 +101,7 @@ function it_calculate_age_from_response(CacheItemPoolInterface $pool, CacheItemI
         $response->getHeader('Age')->willReturn(array('15'));
         $response->getHeader('Expires')->willReturn(array());
 
-        $pool->getItem('e3b717d5883a45ef9493d009741f7c64')->shouldBeCalled()->willReturn($item);
+        $pool->getItem('d20f64acc6e70b6079845f2fe357732929550ae1')->shouldBeCalled()->willReturn($item);
         $item->isHit()->willReturn(false);
 
         // 40-15 should be 25

Diff for: src/CachePlugin.php

@@ -38,7 +38,8 @@ final class CachePlugin implements Plugin
      * @param array                  $config        {
      *
      *     @var bool $respect_cache_headers Whether to look at the cache directives or ignore them
-     *     @var int $default_ttl If we do not respect cache headers or can't calculate a good ttl, use this value.
+     *     @var int $default_ttl If we do not respect cache headers or can't calculate a good ttl, use this value
+     *     @var string $hash_algo The hashing algorithm to use when generating cache keys.
      * }
      */
     public function __construct(CacheItemPoolInterface $pool, StreamFactory $streamFactory, array $config = [])
@@ -150,7 +151,7 @@ private function getCacheControlDirective(ResponseInterface $response, $name)
      */
     private function createCacheKey(RequestInterface $request)
     {
-        return md5($request->getMethod().' '.$request->getUri());
+        return hash($this->config['hash_algo'], $request->getMethod().' '.$request->getUri());
     }
 
     /**
@@ -196,9 +197,11 @@ private function configureOptions(OptionsResolver $resolver)
         $resolver->setDefaults([
             'default_ttl' => null,
             'respect_cache_headers' => true,
+            'hash_algo' => 'sha1',
         ]);
 
         $resolver->setAllowedTypes('default_ttl', ['int', 'null']);
         $resolver->setAllowedTypes('respect_cache_headers', 'bool');
+        $resolver->setAllowedValues('hash_algo', hash_algos());
     }
 }