使用Slim Framework，HTTP缓存不会过期

Question

I'm using Slim framework in order to develop an API.

I wanted to cache some request in the HTTP cache with:

$app->etag('Unique-ID')

But the time expiration didn't seems to work :

$app->expires('10 seconds')

When i look the headers with Chrome, first call i get a 200 Status Code : OK.

Second call, i get a 304 Status Code : OK.

Waiting 30 seconds.

Third call, i still get a 304 Status Code : NOT OK in my mind.

Should i not get a 200 Status Code because the cache is expired ?

Thank you.

Answer 1

In short

Expires header instructs the browser how long it should cache content in client side cache. Browser will serve the content from client side cache until the expiration date is reached.

When client side cache is expired browser will send request to server again. Request includes If-None-Match header with the previous Etag value it received from server. If value of If-None-Match header still matches current Etag value on server it will respond with 304 Not Modified.

When you use Etag and If-None-Match headers and want server to send updated content, value of Etag header must change.

Longer explanation

Lest assume you have the following code.

$app = new \Slim\Slim();

$app->get("/hello", function() use ($app){
    $app->etag("unique-etag-1");
    echo "Hello world.
";
});

$app->run();

Then you make a request.

$ curl --include http://localhost:8080/hello

HTTP/1.1 200 OK
Host: localhost:8080
Connection: close
X-Powered-By: PHP/5.6.2
Content-type: text/html;charset=UTF-8
Etag: "unique-etag-1"

Hello world

On subsequent requests browser will send If-None-Match request header. Value of this header is the same as value of previously received Etag header.

When Slim receives the request it compares the value of If-None-Match header to the value you set with $app->etag() call. If these match 304 Not Modified will be returned.

$ curl --include --header 'If-None-Match: "unique-etag-1"' http://localhost:8080/hello

HTTP/1.1 304 Not Modified
Host: localhost:8080
Connection: close
X-Powered-By: PHP/5.6.2
Etag: "unique-etag-1"
Content-type: text/html; charset=UTF-8

If the content of URI changes or you want to browser to refetch the content for some other reasons, change the value of Etag header.

$app->get("/hello", function() use ($app){
    $app->etag("unique-etag-2");
    echo "Hello world.
";
});

Now when browser makes new request you will get 200 OK response.

curl --include --header 'If-None-Match: "unique-etag-1"' http://localhost:8080/hello
HTTP/1.1 200 OK
Host: localhost:8080
Connection: close
X-Powered-By: PHP/5.6.2
Content-type: text/html;charset=UTF-8
Etag: "unique-etag-2"

Hello world.