[zkserver] Unexpected session error

[marcopeereboom]

Sever errors like this occured in zkserver

2021-03-20 16:08:09 [SES][ERR] sessionWriter write failed cb83f9f185c4b89dff9689a32c
cb742a5194a32d0097030fff2b8800d4d8d106: could not write push: could not marshal

[marcopeereboom]

The failure occurred in the xdr.Marshal call. Unfortunately, the xdr package is too loud in its errors so it always returns a generic could not marshal error. The likely failure is the underlying network connection being wedged somehow. The XDR marshal call does not fail in zkserver since the data has been curated before the marshal occurs. It is likely that this was an OS or network level issue. Under normal circumstances the connection would have been terminated and that obviously did not happen.

func (kx *KX) writeWithKey(data []byte, k *[32]byte) error {
        payload := secretbox.Seal(nil, data, &kx.writeSeq, k)
        incSeq(&kx.writeSeq)
        if uint(len(payload)) > kx.MaxMessageSize {
                return ErrOverflow
        }
        _, err := xdr.Marshal(kx.Conn, payload)
        if err != nil {
                return ErrMarshal // Error that is returned in this case
        }
        return nil
}