Cross-Origin Request Blocked - ajax

Question

So I've got this Go http handler that stores some POST content into the datastore and retrieves some other info in response. On the back-end I use:
func handleMessageQueue(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Access-Control-Allow-Origin", "*")
if r.Method == "POST" {
c := appengine.NewContext(r)
body, _ := ioutil.ReadAll(r.Body)
auth := string(body[:])
r.Body.Close()
q := datastore.NewQuery("Message").Order("-Date")
var msg []Message
key, err := q.GetAll(c, &msg)
if err != nil {
c.Errorf("fetching msg: %v", err)
return
}
w.Header().Set("Content-Type", "application/json")
jsonMsg, err := json.Marshal(msg)
msgstr := string(jsonMsg)
fmt.Fprint(w, msgstr)
return
}
}
In my firefox OS app I use:
var message = "content";
request = new XMLHttpRequest();
request.open('POST', 'http://localhost:8080/msgs', true);
request.onload = function () {
if (request.status >= 200 && request.status < 400) {
// Success!
data = JSON.parse(request.responseText);
console.log(data);
} else {
// We reached our target server, but it returned an error
console.log("server error");
}
};
request.onerror = function () {
// There was a connection error of some sort
console.log("connection error");
};
request.send(message);
The incoming part all works along and such. However, my response is getting blocked. Giving me the following message:
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://localhost:8080/msgs. This can be fixed by moving the resource to the same domain or enabling CORS.
I tried a lot of other things but there is no way I can just get a response from the server. However when I change my Go POST method into GET and access the page through the browser I get the data that I want so bad. I can't really decide which side goes wrong and why: it might be that Go shouldn't block these kinds of requests, but it also might be that my javascript is illegal.

Answer 1

#Egidius, when creating an XMLHttpRequest, you should use
var xhr = new XMLHttpRequest({mozSystem: true});
What is mozSystem?
mozSystem Boolean: Setting this flag to true allows making cross-site connections without requiring the server to opt-in using CORS. Requires setting mozAnon: true, i.e. this can't be combined with sending cookies or other user credentials. This only works in privileged (reviewed) apps; it does not work on arbitrary webpages loaded in Firefox.
Changes to your Manifest
On your manifest, do not forget to include this line on your permissions:
"permissions": {
"systemXHR" : {},
}

Answer 2

You need other headers, not only access-control-allow-origin.
If your request have the "Access-Control-Allow-Origin" header, you must copy it into the response headers, If doesn't, you must check the "Origin" header and copy it into the response. If your request doesn't have Access-Control-Allow-Origin not Origin headers, you must return "*".
You can read the complete explanation here: http://www.html5rocks.com/en/tutorials/cors/#toc-adding-cors-support-to-the-server
and this is the function I'm using to write cross domain headers:
func writeCrossDomainHeaders(w http.ResponseWriter, req *http.Request) {
// Cross domain headers
if acrh, ok := req.Header["Access-Control-Request-Headers"]; ok {
w.Header().Set("Access-Control-Allow-Headers", acrh[0])
}
w.Header().Set("Access-Control-Allow-Credentials", "True")
if acao, ok := req.Header["Access-Control-Allow-Origin"]; ok {
w.Header().Set("Access-Control-Allow-Origin", acao[0])
} else {
if _, oko := req.Header["Origin"]; oko {
w.Header().Set("Access-Control-Allow-Origin", req.Header["Origin"][0])
} else {
w.Header().Set("Access-Control-Allow-Origin", "*")
}
}
w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE")
w.Header().Set("Connection", "Close")
}

Answer 3

You have to placed this code in application.rb
config.action_dispatch.default_headers = {
'Access-Control-Allow-Origin' => '*',
'Access-Control-Request-Method' => %w{GET POST OPTIONS}.join(",")
}