100 Continue

Takeaways

1. The initial part of a request has been received and has not yet been rejected by the server. The server intends to send a final response after the request has been fully received and acted upon.
2. When the request contains an Expect header field that includes a 100-continue expectation, the 100 response indicates that the server wishes to receive the request payload body. The client ought to continue sending the request and discard the 100 response.
3. If the request did not contain an Expect header field containing the 100-continue expectation, the client can simply discard this interim response.

Information

The HTTP 100 Continue informational status response code indicates that everything so far is OK and that the client should continue with the request or ignore it if it is already finished.

To have a server check the request's headers, a client must send Expect: 100-continue as a header in its initial request and receive a 100 Continue status code in response before sending the body.