This means that the server has received the request headers, and that the client should proceed to send the request body (in the case of a request for which a body needs to be sent; for example, a POST request). If the request body is large, sending it to a server when a request has already been rejected based upon inappropriate headers is inefficient. To have a server check if the request could be accepted based on the request’s headers alone, a client must send Expect: 100-continue as a header in its initial request (see RFC 2616: Expect header) and check if a 100 Continue status code is received in response before continuing (or receive 417 Expectation Failed and not continue).
101 Switching Protocols
102 Processing** (WebDAV)
122 Request-URI too long
A Microsoft extension which occurs only in IE7, when the request URI is longer than 2032 characters.