两次致电请求：http 204和200 [英] Two calls on Post request: with http 204 and 200

问题描述

我已在点网核心应用程序中实施了Cors策略：
在 ConfigureServices 下的 Startup.cs 中我添加了以下cors政策

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());
            });

在添加CORS策略后，我面临一个奇怪的问题，从UI进行的每个POST调用中都有两个进行的呼叫：第一个呼叫返回204，其他呼叫返回状态代码200。

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.

推荐答案

第一个是已完成的请求。主要目标是确定实际请求是否可以安全发送。跨站点请求被预检，因为它们可能会影响用户数据。

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.

CORS预检请求是一个CORS请求，用于检查是否

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

这是一个使用两个HTTP请求标头的 OPTIONS 请求：Access-Control-Request -Method和Access-Control-Request-Headers，以及Origin头。

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

在需要时，浏览器会自动发出预检请求。

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

此 HTTP访问控制（CORS）描述条件，如果为true，则请求被预检。

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

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