100 HTTP Status Codes
Information about HTTP status codes 100 to 199, their meaning, and any related restrictions.
100 - Informational
An error occurred on the server and it is unable to complete the request. Information about the error should be returned and displayed unless a HEAD request was performed.
Indicates that request headers have been received and the client should send the request body (if any). This requires the client to send an Expect: 100-continue header in the request.
If an error code is returned then the client should not send the request body.
If the server is unable to support the Expect header then a 417 will be returned.
The client has requested to switch protocols and the server has agreed.
Return response headers before final HTTP response.