Function grin_chain::txhashset::header_extending_readonly

pub fn header_extending_readonly<'a, F, T>(
    handle: &'a mut PMMRHandle<BlockHeader>, 
    store: &ChainStore, 
    inner: F
) -> Result<T, Error> where
    F: FnOnce(&mut HeaderExtension<'_>, &Batch<'_>) -> Result<T, Error>, 

Start a new readonly header MMR extension. This MMR can be extended individually beyond the other (output, rangeproof and kernel) MMRs to allow headers to be validated before we receive the full block data.