1-20 pre inspection request

Pre inspection request

CORS Classification of requests
Client is requesting CORS Excuse time , Depending on the request method and request header , Can speak CORS Your requests fall into two broad categories , Namely ：

1. A simple request

Requests that meet both of the following conditions , It's a simple request ：
（1） Request mode ：GET、POST、HEAD One of the three
（2）HTTP The header information does not exceed the following fields ：
No custom header fields 、Accept、Accept-Language、Content-Language、DPR、Downlink、Save-Data、Viewport-Width、Width、Content-Type( There are only three values application/x-www-form-urlencoded、multipart/form-data、text/plain)

2. Pre inspection request
A request that meets any of the following conditions , All require pre inspection requests ：

• The request method is GET、POST、HEAD、 Requests beyond Method type
• The request header contains a custom header field
• Sent... To the server application/json Formatted data

Before the browser officially communicates with the server , The browser will send OPTION Ask for a pre check , To know if the server allows the actual request , So this time OPTION Ask to be “ Pre inspection request ”. After the server successfully responds to the pre check request , To send a real request , And carry real data .