Function relay_frame 

pub fn relay_frame(
    store: &mut SqliteStore,
    bytes: &[u8],
    session_doc: Option<&str>,
) -> Result<RelayOutput>

Serve one protocol frame from the store, like relayStoreMessage. Rows are committed before the acknowledgement. A frame which cannot be decoded is an Err; every other failure becomes an error frame for the peer.