tailcat: reject malformed ConnBlob public keys

[keyurbodar]

Summary

Reject malformed public keys embedded in connection blobs instead of panicking during CBOR decoding.

Details

NodePublic.UnmarshalBinary passed arbitrary CBOR byte strings directly to key.NodePublicFromRaw32, which panics unless the input is exactly 32 bytes.

Connection blobs can be supplied by users or discovered through DNS TXT records, so malformed input could terminate the CLI or a library process.

This change validates the byte-string length first and returns a descriptive error. Regression tests cover both short and oversized public keys through ParseConnBlob and ParseConnBlobRaw.

Testing

• go test . -run TestParseConnBlobMalformedPublicKey -count=1
• go test . -run TestConnBlob -count=1
• go test . -count=1

[bradfitz]

Thanks!