errno 100 (EPROTO): meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: A protocol layer rejected the operation because its current protocol state or exchange was invalid.

Could be also:
Constant	Type	OS
ERROR_TOO_MANY_SEMAPHORES	Win32 error	Windows
HTTP_STATUS_CONTINUE	HTTP Code	Any
ENETDOWN	errno	Linux
EADDRINUSE	errno	Windows
SYMBOLIC_INITIALIZATION_FAILED	BugCheck Code	Windows

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ENETDOWN	EADDRINUSE

EPROTO

Broader than one malformed payload

EPROTO is a protocol error. On Darwin, the system reference describes it as device-specific and generally separate from a hardware failure. The code can reflect an invalid exchange sequence, unsupported transition, broken framing contract, or another state violation in the responsible protocol layer.

Do not diagnose it as “network down” without evidence. Preserve the protocol name, role, connection or device state, last successful transition, and the request that triggered the error. A reconnect may be appropriate for a stateful session, but only after determining whether the peer can have processed the request.

Useful separation

EBADMSG points at a bad message; this result can include a bad state transition or protocol contract failure.
EPROTONOSUPPORT means no implementation for a protocol; this result means a failure while using one.
Retain protocol traces with secrets removed, rather than only the final errno.

References

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