Mod note: This question is about why XMLHttpRequest/fetch/etc. on the browser are subject to the Same Access Policy restrictions (you get errors mentioning CORB or CORS) while Postman is not. This question is not about how to fix a "No 'Access-Control-Allow-Origin'..." error. It's about why they happen.
Please stop posting:
CORS configurations for every language/framework under the sun. Instead find your relevant language/framework's question.
3rd party services that allow a request to circumvent CORS
Command line options for turning off CORS for various browsers
I am trying to do authorization using JavaScript by connecting to the RESTful API built-in Flask. However, when I make the request, I get the following error:
XMLHttpRequest cannot load http://myApiUrl/login.
No 'Access-Control-Allow-Origin' header is present on the requested resource.
Origin 'null' is therefore not allowed access.
I know that the API or remote resource must set the header, but why did it work when I made the request via the Chrome extension Postman?
This is the request code:
$.ajax({
type: 'POST',
dataType: 'text',
url: api,
username: 'user',
password: 'pass',
crossDomain: true,
xhrFields: {
withCredentials: true,
},
})
.done(function (data) {
console.log('done');
})
.fail(function (xhr, textStatus, errorThrown) {
alert(xhr.responseText);
alert(textStatus);
});
If I understood it right you are doing an XMLHttpRequest to a different domain than your page is on. So the browser is blocking it as it usually allows a request in the same origin for security reasons. You need to do something different when you want to do a cross-domain request.
When you are using Postman they are not restricted by this policy. Quoted from Cross-Origin XMLHttpRequest:
Regular web pages can use the XMLHttpRequest object to send and receive data from remote servers, but they're limited by the same origin policy. Extensions aren't so limited. An extension can talk to remote servers outside of its origin, as long as it first requests cross-origin permissions.
WARNING: Using Access-Control-Allow-Origin: * can make your API/website vulnerable to cross-site request forgery (CSRF) attacks. Make certain you understand the risks before using this code.
It's very simple to solve if you are using PHP. Just add the following script in the beginning of your PHP page which handles the request:
<?php header('Access-Control-Allow-Origin: *'); ?>
If you are using Node-red you have to allow CORS in the node-red/settings.js file by un-commenting the following lines:
// The following property can be used to configure cross-origin resource sharing
// in the HTTP nodes.
// See https://github.com/troygoode/node-cors#configuration-options for
// details on its contents. The following is a basic permissive set of options:
httpNodeCors: {
origin: "*",
methods: "GET,PUT,POST,DELETE"
},
If you are using Flask same as the question; you have first to install flask-cors
pip install -U flask-cors
Then include the Flask cors package in your application.
from flask_cors import CORS
A simple application will look like:
from flask import Flask
from flask_cors import CORS
app = Flask(__name__)
CORS(app)
#app.route("/")
def helloWorld():
return "Hello, cross-origin-world!"
For more details, you can check the Flask documentation.
Because
$.ajax({type: "POST" - calls OPTIONS
$.post( - calls POST
Both are different. Postman calls "POST" properly, but when we call it, it will be "OPTIONS".
For C# web services - Web API
Please add the following code in your web.config file under the <system.webServer> tag. This will work:
<httpProtocol>
<customHeaders>
<add name="Access-Control-Allow-Origin" value="*" />
</customHeaders>
</httpProtocol>
Please make sure you are not doing any mistake in the Ajax call.
jQuery
$.ajax({
url: 'http://mysite.microsoft.sample.xyz.com/api/mycall',
headers: {
'Content-Type': 'application/x-www-form-urlencoded'
},
type: "POST", /* or type:"GET" or type:"PUT" */
dataType: "json",
data: {
},
success: function (result) {
console.log(result);
},
error: function () {
console.log("error");
}
});
Note: If you are looking for downloading content from a third-party website then this will not help you. You can try the following code, but not JavaScript.
System.Net.WebClient wc = new System.Net.WebClient();
string str = wc.DownloadString("http://mysite.microsoft.sample.xyz.com/api/mycall");
Deep
In the below investigation as API, I use http://example.com instead of http://myApiUrl/login from your question, because this first one working. I assume that your page is on http://my-site.local:8088.
NOTE: The API and your page have different domains!
The reason why you see different results is that Postman:
set header Host=example.com (your API)
NOT set header Origin
Postman actually not use your website url at all (you only type your API address into Postman) - he only send request to API, so he assume that website has same address as API (browser not assume this)
This is similar to browsers' way of sending requests when the site and API has the same domain (browsers also set the header item Referer=http://my-site.local:8088, however I don't see it in Postman). When Origin header is not set, usually servers allow such requests by default.
This is the standard way how Postman sends requests. But a browser sends requests differently when your site and API have different domains, and then CORS occurs and the browser automatically:
sets header Host=example.com (yours as API)
sets header Origin=http://my-site.local:8088 (your site)
(The header Referer has the same value as Origin). And now in Chrome's Console & Networks tab you will see:
When you have Host != Origin this is CORS, and when the server detects such a request, it usually blocks it by default.
Origin=null is set when you open HTML content from a local directory, and it sends a request. The same situation is when you send a request inside an <iframe>, like in the below snippet (but here the Host header is not set at all) - in general, everywhere the HTML specification says opaque origin, you can translate that to Origin=null. More information about this you can find here.
fetch('http://example.com/api', {method: 'POST'});
Look on chrome-console > network tab
If you do not use a simple CORS request, usually the browser automatically also sends an OPTIONS request before sending the main request - more information is here. The snippet below shows it:
fetch('http://example.com/api', {
method: 'POST',
headers: { 'Content-Type': 'application/json'}
});
Look in chrome-console -> network tab to 'api' request.
This is the OPTIONS request (the server does not allow sending a POST request)
You can change the configuration of your server to allow CORS requests.
Here is an example configuration which turns on CORS on nginx (nginx.conf file) - be very careful with setting always/"$http_origin" for nginx and "*" for Apache - this will unblock CORS from any domain (in production instead of stars use your concrete page adres which consume your api)
location ~ ^/index\.php(/|$) {
...
add_header 'Access-Control-Allow-Origin' "$http_origin" always;
add_header 'Access-Control-Allow-Credentials' 'true' always;
if ($request_method = OPTIONS) {
add_header 'Access-Control-Allow-Origin' "$http_origin"; # DO NOT remove THIS LINES (doubled with outside 'if' above)
add_header 'Access-Control-Allow-Credentials' 'true';
add_header 'Access-Control-Max-Age' 1728000; # cache preflight value for 20 days
add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
add_header 'Access-Control-Allow-Headers' 'My-First-Header,My-Second-Header,Authorization,Content-Type,Accept,Origin';
add_header 'Content-Length' 0;
add_header 'Content-Type' 'text/plain charset=UTF-8';
return 204;
}
}
Here is an example configuration which turns on CORS on Apache (.htaccess file)
# ------------------------------------------------------------------------------
# | Cross-domain Ajax requests |
# ------------------------------------------------------------------------------
# Enable cross-origin Ajax requests.
# http://code.google.com/p/html5security/wiki/CrossOriginRequestSecurity
# http://enable-cors.org/
# <IfModule mod_headers.c>
# Header set Access-Control-Allow-Origin "*"
# </IfModule>
# Header set Header set Access-Control-Allow-Origin "*"
# Header always set Access-Control-Allow-Credentials "true"
Access-Control-Allow-Origin "http://your-page.com:80"
Header always set Access-Control-Allow-Methods "POST, GET, OPTIONS, DELETE, PUT"
Header always set Access-Control-Allow-Headers "My-First-Header,My-Second-Header,Authorization, content-type, csrf-token"
Applying a CORS restriction is a security feature defined by a server and implemented by a browser.
The browser looks at the CORS policy of the server and respects it.
However, the Postman tool does not bother about the CORS policy of the server.
That is why the CORS error appears in the browser, but not in Postman.
The error you get is due to the CORS standard, which sets some restrictions on how JavaScript can perform ajax requests.
The CORS standard is a client-side standard, implemented in the browser. So it is the browser which prevent the call from completing and generates the error message - not the server.
Postman does not implement the CORS restrictions, which is why you don't see the same error when making the same call from Postman.
Why doesn't Postman implement CORS? CORS defines the restrictions relative to the origin (URL domain) of the page which initiates the request. But in Postman the requests doesn't originate from a page with an URL so CORS does not apply.
Solution & Issue Origins
You are making a XMLHttpRequest to different domains, example:
Domain one: some-domain.com
Domain Two: some-different-domain.com
This difference in domain names triggers CORS (Cross-Origin Resource Sharing) policy called SOP (Same-Origin Policy) that enforces the use of same domains (hence Origin) in Ajax, XMLHttpRequest and other HTTP requests.
Why did it work when I made the request via the Chrome extension
Postman?
A client (most Browsers and Development Tools) has a choice to enforce the Same-Origin Policy.
Most browsers enforce the policy of Same-Origin Policy to prevent issues related to CSRF (Cross-Site Request Forgery) attack.
Postman as a development tool chooses not to enforce SOP while some browsers enforce, this is why you can send requests via Postman that you cannot send with XMLHttpRequest via JS using the browser.
For browser testing purposes:
Windows - Run:
chrome.exe --user-data-dir="C://Chrome dev session" --disable-web-security
The command above will disable chrome web security. So for example if you work on a local project and encounter CORS policy issue when trying to make a request, you can skip this type of error with the above command. Basically it will open a new chrome session.
You might also get this error if your gateway timeout is too short and the resource you are accessing takes longer to process than the timeout. This may be the case for complex database queries etc. Thus, the above error code can be disguishing this problem. Just check if the error code is 504 instead of 404 as in Kamil's answer or something else. If it is 504, then increasing the gateway timeout might fix the problem.
In my case the CORS error could be removed by disabling the same origin policy (CORS) in the Internet Explorer browser, see How to disable same origin policy Internet Explorer. After doing this, it was a pure 504 error in the log.
To resolve this issue, write this line of code in your doGet() or doPost() function whichever you are using in backend
response.setHeader("Access-Control-Allow-Origin", "*");
Instead of "*" you can type in the website or API URL endpoint which is accessing the website else it will be public.
Your IP address is not whitelisted, so you are getting this error.
Ask the backend staff to whitelist your IP address for the service you are accessing.
Access-Control-Allow-Headers
For me I got this issue for different reason, the remote domain was added to origins the deployed app works perfectly except one end point I got this issue:
Origin https://mai-frontend.vercel.app is not allowed by Access-Control-Allow-Origin. Status code: 500
and
Fetch API cannot load https://sciigo.herokuapp.com/recommendations/recommendationsByUser/8f1bb29e-8ce6-4df2-b138-ffe53650dbab due to access control checks.
I discovered that my Heroku database table does not contains all the columns of my local table after updating Heroku database table everything worked well.
It works for me by applying this middleware in globally:
<?php
namespace App\Http\Middleware;
use Closure;
class Cors {
public function handle($request, Closure $next) {
return $next($request)
->header('Access-Control-Allow-Origin', '*')
->header('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS')
->header('Access-Control-Allow-Headers', "Accept,authorization,Authorization, Content-Type");
}
}
I have the following code in my component:
fetch('https://domain.com/api', {
method: 'POST',
headers: {'Accept': 'application/json', 'Content-Type': 'application/json'},
body: JSON.stringify({
key: 'value'
})
}).
then((response) => {
console.log('Done', response);
});
And every time the request is a GET (checked server logs). I thought it was something to do with CORS (but apparently no such thing in react-native) and ATS (but already turned off by default, plus my domain is HTTPS). I've tried from a browser and from a curl and it worked perfectly, so a priori no issue on server configuration. Any idea what's going on here?
I'm using the latest react-native version.
After further digging, it was definitely an issue with the API + fetch. I was missing a slash at the end of the URL and the API issued a 301, that fetch didn't handle correctly. So I don't know if there is something to fix in the fetch function (and underlying mechanisms) but this fixed my issue :)
When a POST is redirected (in my case from http to https) it gets transformed into a GET. (Don't know why...)
I have this code on my Angular App controller:
$http.jsonp('http://192.168.1.210/json', config).success(function (data) {
vm.lightSensor = data.a0-vm.lightThreshold;
vm.detected = (data.d2==1) ? 'Yes' : 'No';
vm.toggle = (data.d7==1) ? 'on' : 'off';
vm.jsonerror = false;
}).error(function (data, status, headers, config) {
alert(status);
vm.jsonerror = true;
});
It throws a 404 status error when I do the alert, however, this happens on Safari iOS but not on iOS Chrome, where the request works fine.
I think, as the server is an Arduino, that it may be something to do with the request headers that Safari iOS is sending, that maybe the Arduino server doesn't like and returns a 404 error.
I tried to debug it with weinre, but it doesn't show any xhr requests (at least for me).
What other not-too-tedious ways are there to debug the request so I can see what headers are being sent considering that I don't have a Mac?
I already solved it. I could look at the headers by modifying the Arduino server to output the headers in the arduino serial console.
Turns out the problem was the arduino server itself, it didn't return a 200 code so it failed in Safari iOS. Somehow it still worked on the rest of the browsers, but I have no clue why.
I'm developing an iPhone app and the plan is to send a JSON packet every so often from the app to a local webserver. To do this, I had planned to use Alamofire. My POST method looks like this:
Alamofire.request(Alamofire.Method.POST, "http://XXX.XX.X.XX:3000/update", parameters: dictPoints, encoding: .JSON)
.responseJSON {(request, response, JSON, error) in
println(JSON)
}
The IP address is marked out, but I've made sure that this corresponds to the IPv4 wireless address of my local server. The server is set to listen to port 3000. The server configuration looks like this:
var express = require('express');
var app = express();
var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/test');
var db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function (callback) {
console.log("MongoDB connection is open.");
});
// Mongoose Schema definition
var Schema = mongoose.Schema;
var LocationSchema = new Schema({
//some schema here
});
// Mongoose Model definition
var LocationsCollection = mongoose.model('locations', LocationSchema);
// URL management
app.get('/', function (req, res) {
res.sendFile(__dirname + '/index.html');
});
app.get('/update', function (req, res) {
console.log("Got something from the phone!");
});
// Start the server
var server = app.listen(3000, function () {
var host = server.address().address
var port = server.address().port
console.log('App listening at %s:%s',host, port)
})
So, this server seems to work ok. I can test it in my browser and type the URL: http://127.0.0.1:3000 and it will feed me the index.html file. If I type in http://127.0.0.1:3000/update... then I get the "Got something from the phone!" message. However, when I run my app (making sure my phone is on the same wireless network as the server) and the Alamofire method gets called... the response I get is nil. I also don't see the "Got something from the phone!" message. Can anyone let me know why that would be happening... or better yet, how to fix it?
A few thoughts:
You are creating a POST request in Alamofire, but you've told Express to handle GET requests for /update. Use app.post(...) if you want to handle it as a POST.
Your Alamofire code is looking for JSON response, but you don't appear to be creating a JSON response. In the short term, you could use responseString rather than responseJSON, but I presume you really want to change your web service to respond with JSON (to make it easier for the app to parse the responses).
Your Alamofire code sending a JSON request (but clearly when you send a request via the web browser, it's not JSON). Are you sure you wanted to send JSON request? (This is not to be confused with the JSON response issue.) Did you want to use the .URL encoding type parameter, rather than .JSON?
Whenever you have a request that works correctly from a web browser, but not from the app, it's useful to watch both using a tool like Charles and you can then compare how they differ and diagnose the source of the different behavior.
If you are running Express server and iOS Simulator on the same machine, try to use http://0.0.0.0:<port>/<url> instead of the actual IP, it helped in my case.
It sounds like the node server is not bound to the address you expect it to be. You should verify that when you type in the actual IP address in your "http://XXX.XX.X.XX:3000/update" in your web browser that it responds. Your question details suggest you've just been using the loopback address.
Is there any way to accept POST type requests without using Nerve lib in Node.js?
By default the http.Server class of Node.js accepts any http method.
You can get the method using request.method (api link).
Example:
var sys = require('sys'),
http = require('http');
http.createServer(function (request, response) {
response.writeHead(200, {'Content-Type': 'text/plain'});
response.write(request.method);
response.end();
}).listen(8000);
sys.puts('Server running at http://127.0.0.1:8000/');
This will create a simple http server on the port 8000 that will echo the method used in the request.
If you want to get a POST you should just check the request.method for the string "POST".
Update regarding response.end:
Since version 0.1.90, the function to close the response is response.end instead of response.close. Besides the name change, end can also send data and close the response after this data is sent unlike close. (api example)