HRESULT 0x801901A1 (HTTP_E_STATUS_EXPECTATION

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Description:

The server returned HTTP 417 Expectation Failed because it could not meet the request expectation.

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HTTP_E_STATUS_RANGE_NOT_SATISFIABLE	HTTP_E_STATUS_SERVER_ERROR

HTTP_E_STATUS_EXPECTATION_FAILED

HTTP_E_STATUS_EXPECTATION_FAILED maps to HTTP 417 Expectation Failed. The server cannot meet the expectation expressed in the request, commonly an Expect: 100-continue header used with large request bodies.

What to check

Capture the full Expect header and determine whether the endpoint or an intermediary supports it.
Check for legacy proxies that reject or mishandle 100-continue.
Change the client behaviour only after verifying that the request remains correctly framed and that large uploads will not be sent unnecessarily.

RFC 9110: 417 Expectation Failed

RFC 9112: HTTP/1.1 expectation handling

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