417
Client Error
417 Expectation Failed
The server cannot meet the requirements of the Expect request-header field.
Definition (RFC 9110)
HTTP status code 417 417 Expectation Failed is defined in RFC 9110 (HTTP Semantics), Section 15.5.18 — the current authoritative specification for HTTP semantics, published June 2022, which obsoletes the older RFC 7231 and RFC 2616.
Description
417 Expectation Failed is returned when the server cannot meet the expectation given in an Expect request header. The most common use case is Expect: 100-continue, which allows a client to check whether the server will accept a large request body before actually sending it.
Common Causes
- Client sending
Expect: 100-continuebut server doesn't support it - Proxy stripping or mishandling the
Expectheader - Outdated HTTP client with incorrect expectation headers
How to Fix
- Remove the
Expect: 100-continueheader if the server doesn't support it - Update your HTTP client or library to handle server responses correctly
- Use a direct connection if a proxy is mishandling the header
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