CachedClient: header 'Last-Modified' has higher priority than 'ETag'

Some GitHub responses contain static ETag 'nil' and they control caching by timestamps.

Author: milo

src/Github/Http/CachedClient.php

@@ -75,10 +75,10 @@ public function request(Request $request)
 			}
 
 			/** @var $cached Response */
-			if ($cached->hasHeader('ETag')) {
-				$request->addHeader('If-None-Match', $cached->getHeader('ETag'));
-			} elseif ($cached->hasHeader('Last-Modified')) {
+			if ($cached->hasHeader('Last-Modified')) {
 				$request->addHeader('If-Modified-Since', $cached->getHeader('Last-Modified'));
+			} elseif ($cached->hasHeader('ETag')) {
+				$request->addHeader('If-None-Match', $cached->getHeader('ETag'));
 			}
 		}
 

tests/Github/Http/CachedClient.phpt

@@ -184,6 +184,35 @@ class CachingTestCase extends Tester\TestCase
 	}
 
 
+	public function testPreferIfModifiedAgainstETag()
+	{
+		$this->innerClient->onRequest = function (Http\Request $request) {
+			Assert::false($request->hasHeader('If-None-Match'));
+			Assert::false($request->hasHeader('If-Modified-Since'));
+
+			return new Http\Response(200, ['Last-Modified' => 'today', 'ETag' => 'e-tag'], "response-{$request->getContent()}");
+		};
+
+		$response = $this->client->request(new Http\Request('', '', [], '1'));
+		Assert::same('response-1', $response->getContent());
+		Assert::same(1, $this->innerClient->requestCount);
+
+
+		$this->innerClient->onRequest = function (Http\Request $request) {
+			Assert::false($request->hasHeader('ETag'));
+			Assert::same('today', $request->getHeader('If-Modified-Since'));
+
+			return new Http\Response(304, [], "response-{$request->getContent()}");
+		};
+
+		$response = $this->client->request(new Http\Request('', '', [], '2'));
+		Assert::same('response-1', $response->getContent());
+		Assert::type('Milo\Github\Http\Response', $response->getPrevious());
+		Assert::same(304, $response->getPrevious()->getCode());
+		Assert::same(2, $this->innerClient->requestCount);
+	}
+
+
 	public function testRepeatedRequest()
 	{
 		$request = new Http\Request('', '', [], 'same');