What does errno 104 (EBADMSG) mean?

EBADMSG

EBADMSG is defined by the UCRT as a POSIX compatibility constant. It describes a message that reached a receiving interface but could not be accepted as a valid message for that interface. The value by itself does not identify a Win32 API, a Winsock call, or a particular wire protocol.

For a decoder, queue adapter, RPC layer, or portability library, the important boundary is usually between received bytes and accepted message. A frame can be present yet still fail a length check, a required-field check, a checksum or signature check, a type discriminator, or a version-specific rule.

Useful evidence to keep

• The API or library that produced EBADMSG, its return value, and the error value captured immediately afterwards.
• The protocol stage, expected message type or version, declared length, and validation rule that rejected the input.
• A bounded, redacted representation of the header or message metadata when it is safe to retain it.

EBADMSG concerns one unacceptable message. It should not be treated as a synonym for a lost connection or for the broader protocol-state failure represented by EPROTO.

References

• Microsoft: errno constants
• POSIX: <errno.h>

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