Under what circumstances will the server return 100? What is the application scenario?

100 in the HTTP status code indicates that the server has received the request from the client and expects the client to continue to send the request.

Baidu encyclopedia explains that the client should continue to send requests. This temporary response is used to inform the client that some of its requests have been received by the server and have not yet been rejected. The client should continue to send the rest of the request or ignore the response if the request has been completed. The server must send a final response to the client after the request is completed.

I don"t quite understand what this specific application scenario is.

Http protocol

Mar.22,2021

http 100-continue is used for the client to consult the server before sending POST data to the server to see whether the server processes POST data. If not, the client does not upload POST data. If it does, POST uploads the data. In real applications, the 100-continue protocol is usually used only when POST big data is used.
1) if the client has POST data to upload, you can consider using the 100-continue protocol. Add header {"Expect": "100-continue"}
2) the server returns 100 or error code after receiving the request under the correct circumstances.

see this article: https://zhuanlan.zhihu.com/p/.

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