HTTP status codes - Information responses

100 Continue
This interim response indicates that everything so far is OK and that the client should continue with the request or ignore it if it is already finished.
101 Switching Protocol
This code is sent in response to an Upgrade request header by the client, and indicates the protocol the server is switching to.
102 Processing (WebDAV)
This code indicates that the server has received and is processing the request, but no response is available yet.