100 Continue

The initial part of a request has been received and has not yet been rejected by the server. The server intends to send a final response after the request has been fully received and acted upon.

When the request contains an Expect header field that includes a 100-continue expectation, the 100 response indicates that the server wishes to receive the request payload body¹. The client ought to continue sending the request and discard the 100 response.

If the request did not contain an Expect header field containing the 100-continue expectation, the client can simply discard this interim response.

¹ Expect RFC7231 Section 5.1.1
Source: RFC7231 Section 6.1.1

100 Code references

Go HTTP Status Constant http.StatusContinue
Python3+ HTTP Status Constant http.client.CONTINUE
Python3.5+ HTTP Status Constant http.HTTPStatus.CONTINUE
Rails HTTP Status Symbol :continue
Symfony HTTP Status Constant Response::HTTP_CONTINUE

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