HTTP status code

The HTTP 100 status code stands for "Continue". It is an informational response indicating that the initial part of the request has been received and the client should continue sending the rest of the request.

When is HTTP 100 Used?

• It is primarily used with large requests that include an "Expect: 100-continue" header.
• The client sends a request header first, waits for a 100 Continue response, and then sends the request body.
• This prevents the client from sending a large payload if the server is going to reject the request early (e.g., due to authentication failure).

Example Scenario

A client wants to upload a large file but first checks if the server is ready to accept it before sending the full data.

Example

Client Request (Sending Headers First)

  
        POST /upload HTTP/1.1
        Host: example.com
        Content-Length: 5000000
        Expect: 100-continue

    

Server Response (Allowing to Continue)

  
        HTTP/1.1 100 Continue
    

Client Sends the Body (After Receiving 100 Continue)

    
        (binary file data...)
    

Summary

HTTP 100 is an intermediate response used to indicate that the client can proceed with sending the request body. It helps optimize large data transfers by ensuring the server is ready to accept the request before the client sends it.