Two calls on Post request: with http 204 and 200

Question

I have implemented Cors policy in dot net core application: In Startup.cs under ConfigureServices I have added the following cors policy

services.AddCors(options =>{
                options.AddPolicy("CorsPolicy",
                    builder => builder.AllowAnyOrigin()
                    .AllowAnyMethod()
                    .AllowAnyHeader()
                    .AllowCredentials());
            });

I'm facing a strange issue after adding CORS policy, on every POST call from UI there are two calls made: first calls returns with 204 and other call returns the data with 200 status code.

score 21 · Accepted Answer · edited Jun 20 '20 at 09:12

21

First one is a preflighted request. The main goal is to determinate whether the actual request is safe to send. Cross-site requests are preflighted since they may have implications to user data.

A CORS preflight request is a CORS request that checks to see if the CORS protocol is understood.

It is an OPTIONS request using two HTTP request headers: Access-Control-Request-Method and Access-Control-Request-Headers, and the Origin header.

A preflight request is automatically issued by a browser when needed.

This HTTP access control (CORS) describe conditions that if true then request is preflighted.

edited Jun 20 '20 at 09:12

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answered Aug 07 '17 at 10:23

Set

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Is there a way to disable this pre-flight calls? I'm using angularjs on the front-end. – Nikitesh Aug 07 '17 at 10:33
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@NikiteshKolpe look into SO [How to disable OPTIONS request](https://stackoverflow.com/questions/29954037/how-to-disable-options-request) – Set Aug 07 '17 at 11:32
have the same 'issue'. Now it makes sense. I was debugging my Angular code, if there somehow was 2 calls – Johansrk Aug 09 '18 at 11:01
So the `204 No Content` request is the CORS preflight request? – Kyle Vassella Oct 11 '18 at 19:37

Two calls on Post request: with http 204 and 200

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