What does HTTP status 417 (Expectation Failed) mean?

 
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HTTP_STATUS_RANGE_NOT_SATISFIABLE HTTP_STATUS_TEAPOT

HTTP_STATUS_EXPECTATION_FAILED

The common case is an Expect: 100-continue request where an origin or intermediary cannot honor the expectation. The failure can occur before the client sends a large body.

Inspect the Expect header and proxy behavior. Remove unsupported expectations only when the endpoint does not require them; do not confuse this with ordinary authentication or validation failures.

The best-known trigger is an Expect request-header value that the receiving server cannot satisfy. A client can remove or change the expectation only if doing so preserves the request semantics. When a proxy is involved, determine which hop generated 417 because expectation handling can differ between intermediaries and the origin.

RFC 9110: HTTP Semantics


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