Client with :ajax fails with Assert failed: (string? prefixed-pstr)

[martinhynar]

Hi,

I have client that wants to communicate with backend over Ajax. I first configured the client part with :type :auto and on my local machine it ended up to be always :ws but then I realized that the target Apache is 2.2 which is missing WebSockets support, so I changed to :type :ajax. Until that, all client/server communication was just fine, but with :ajax I immediately started to receive bellow exception. Note that there is still no Apache. It is just lein run, starting http-kit.

2015-Jan-16 11:41:28 +0100 localhost INFO [app.ui-backend.websockets] - Client connected :client-4f912139
Fri Jan 16 11:41:33 CET 2015 [worker-1] ERROR - POST /ws
java.lang.AssertionError: Assert failed: (string? prefixed-pstr)
    at taoensso.sente$unpack.invoke(sente.clj:242)
    at taoensso.sente$make_channel_socket_BANG_$fn__13809.invoke(sente.clj:440)
    at app.rest.routes$fn__16923.invoke(routes.clj:226)
        ...

I thought it is complaining about non-prefixed message id, but I am sending this [:app/login {:username "" :password ""}].

On server side, I use Stuart Sierra's component library and I enrich each request coming in with some references to components. The wrapper function is bellow. In fact, ws is map containing ajax-post-fn function that is called on the request later in POST /ws route.

(defn wrap-app-component [f ws]
  (fn [req] (f (assoc req ::ws ws))))

I tried to read body from the failing POST request, and it has following form:

_=1421407295204&ppstr=%2B%5B%5B%3Aapp%2Flogin%20%7B%3Ausername%20%22test%22%2C%20%3Apassword%20%22%22%7D%5D%200%5D&csrf-token=6f279a6a-87b4-4a5a-b4a4-67b5be2ab936

I am using sente "1.2.0" and http-kit "2.1.19". Tried also sente "1.3.0RC2", same result.

[ptaoussanis]

Hi Martin,

Could you please try the Sente reference example over Ajax (it randomly selects :ajax or :ws) and let me know if you're still seeing the same problem on your system? Thanks!

[martinhynar]

The reference example work just fine. For both :ws and :ajax I saw clients popping up.

[ptaoussanis]

Can you try run lein clean (or remove your target/ dir) and try your own project again?

[martinhynar]

Still the same.
I feel like there is something missing in the request when it is passed to ajax-post-fn. I printed it to console:

{:remote-addr "127.0.0.1",
 :headers
 {"origin" "http://localhost:8080",
  "x-requested-with" "XMLHTTPRequest",
  "host" "localhost:8080",
  "user-agent"
  "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.95 Safari/537.36",
  "content-type" "application/x-www-form-urlencoded; charset=UTF-8",
  "cookie" "ring-session=a84692cf-f878-4b99-b229-8620f287ae2c",
  "content-length" "165",
  "referer" "http://localhost:8080/ui",
  "connection" "keep-alive",
  "accept" "*/*",
  "accept-language" "en-US,en;q=0.8,cs;q=0.6",
  "accept-encoding" "gzip, deflate"},
 :async-channel #<AsyncChannel /127.0.0.1:8080<->/127.0.0.1:35818>,
 :server-port 8080,
 :content-length 165,
 :websocket? false,
 :content-type "application/x-www-form-urlencoded",
 :character-encoding "UTF-8",
 :uri "/ws",
 :server-name "localhost",
 :query-string nil,
 :body #<BytesInputStream BytesInputStream[len=165]>,
 :scheme :http,
 :request-method :post}

I see no :params key. The :ppstr which is read from params in ajax-post-fn is taken from there. Am I missing some wrapper that will populate it from body data?

[ptaoussanis]

I see no :params key. The :ppstr which is read from params in ajax-post-fn is taken from there. Am I missing some wrapper that will populate it from body data?

That's a good catch. Are you using Ring's wrap-params and wrap-keyword-params middleware? If not, you should be seeing a warning being logged on the server side.

[martinhynar]

That was it!

I was missing both wrappers and they have to be in that specific order of application, first wrap-params then wrap-keyword-params. (just for the record, if somebody ever tackles the same problem)

I saw that warning when I was trying with sente '1.3.0-RC2' but it was missing with "1.2.0" and I got feeling that it is because of some new functionality.

Thanks for helping!

[ptaoussanis]

No problem, happy you've got it working :-)

[seancorfield]

Just FYI, this caught me out too when Ring's site wrapper was deprecated. I wonder if it's worth Sente providing a minimum default wrapper?

[ptaoussanis]

@seancorfield Hey Sean, what version did you have the trouble with? v1.3+ issues a warning when the necessary middleware is missing.

[seancorfield]

The warning's easy to miss tho' - as shown above. It was a while back but I think what happened was that I updated Ring, found site was missing (or deprecated? I don't recall) and it took me a while to figure out what Sente needed in order to function correctly. If Sente requires it, why not throw an exception?

[ptaoussanis]

If Sente requires it, why not throw an exception?

This is true ;-) Will make the change tomorrow. Appreciate the input!