Expect

States an expectation the server must fulfill before processing a request.

Use Expect: 100-continue to avoid sending a large body before the server accepts the request headers. Do not invent unsupported expectations.

httpheaderrequestuploads

Reference (http)

Expect: 100-continue

Use Expect: 100-continue to avoid sending a large body before the server accepts the request headers. Do not invent unsupported expectations.

Common mistakes

Sending the body immediately while assuming an interim 100 response is guaranteed.

IANA registry: http-fields/field-names

Sources