HTTP Status Code: 100 Continue

The HTTP status code 100 Continue is part of the 1xx series, which represents informational responses. Specifically, 100 Continue is used to indicate that the initial part of the client's request has been received by the server, and the server is prompting the client to proceed with sending the remainder of the request. This status code is typically utilized in scenarios involving large payloads or in situations where a server wants to confirm that the client can continue before processing the entire request.

Conditions for Receiving 100 Continue.

The HTTP status code 100 Continue is received under specific conditions when a client sends a request with an Expect: 100-continue header. Here are the conditions for receiving the 100 Continue status:

Expect Header Present: The client includes the Expect: 100-continue header in its initial request. This header serves as a signal to the server that the client expects to receive a 100 Continue response before proceeding to send the full request payload.
Server Readiness: The server is ready and able to receive the remaining part of the client's request. The server may use this status code to communicate to the client that it can proceed with sending the entire request payload.
Client's Willingness to Wait: The client is willing to wait for the server's confirmation before sending the full payload. By including the Expect: 100-continue header, the client indicates its intention to wait for the server's acknowledgment before proceeding with the request.

Example:

Client Request.

POST /upload HTTP/1.1
Host: example.com
Content-Length: 10000
Expect: 100-continue

<... additional headers and payload ...>

Server Response (100 Continue).

HTTP/1.1 100 Continue

In this example, the conditions are met as the client includes the Expect: 100-continue header, signaling its willingness to wait for acknowledgment, and the server responds with a 100 Continue status, indicating readiness to receive the remaining payload.

Use Cases of 100 Continue:

Large File Uploads: When a client is uploading a large file, it may include the Expect: 100-continue header to ensure the server is ready before sending the entire file.
Resource-Intensive Requests: In situations where the server needs to perform resource-intensive processing, it can use 100 Continue to signal the client to proceed only if the server is prepared to handle the request.

How To Handle 100 Continue Status Code?

Handling the HTTP status code 100 Continue involves specific actions on both the client and server sides. This status code is utilized in scenarios where the client includes the Expect: 100-continue header in the request, indicating its intention to wait for acknowledgment from the server before sending the full payload. Here's how to handle the 100 Continue status:

Client's Responsibility: The client should include the Expect: 100-continue header in the initial request if it is willing to wait for the server's confirmation before sending the full payload.
Wait for Confirmation: Upon receiving a 100 Continue response, the client can proceed to send the rest of the request.
Handling Delays: If the client doesn't receive a 100 Continue response, it may choose to wait for a reasonable amount of time before deciding whether to proceed or take appropriate action.

Best Practice.

Use the 100 Continue mechanism in scenarios where it can improve the efficiency of data transmission, especially for large payloads.
Implement mechanisms to handle situations where the client does not receive a 100 Continue response within a reasonable timeframe.
Clients may choose to wait for a specific duration and then decide whether to proceed without acknowledgment.
Both clients and servers should gracefully handle situations where a 100 Continue response is expected but not received, allowing for sensible fallback mechanisms.

Conclusion.

HTTP status code 100 Continue facilitates more efficient communication between clients and servers, especially in scenarios involving substantial data transfers. Clients using the Expect: 100-continue header can ensure that the server is ready to receive the full request payload before committing to the transmission. This status code contributes to the overall optimization of data exchange in the HTTP protocol.