Module zcash_client_backend::data_api::chain

Tools for blockchain validation & scanning

Examples

use tempfile::NamedTempFile;
use zcash_primitives::{
    consensus::{BlockHeight, Network, Parameters}
};

use zcash_client_backend::{
    data_api::{
        BlockSource, WalletRead, WalletWrite,
        chain::{
            validate_chain,
            scan_cached_blocks,
        },
        error::Error,
    },
};

use zcash_client_sqlite::{
    BlockDb,
    WalletDb,
    error::SqliteClientError,
    wallet::{rewind_to_height},
    wallet::init::{init_wallet_db},
};

let network = Network::TestNetwork;
let cache_file = NamedTempFile::new()?;
let db_cache = BlockDb::for_path(cache_file)?;
let db_file = NamedTempFile::new()?;
let db_read = WalletDb::for_path(db_file, network)?;
init_wallet_db(&db_read)?;

let mut db_data = db_read.get_update_ops()?;

// 1) Download new CompactBlocks into db_cache.

// 2) Run the chain validator on the received blocks.
//
// Given that we assume the server always gives us correct-at-the-time blocks, any
// errors are in the blocks we have previously cached or scanned.
if let Err(e) = validate_chain(&network, &db_cache, db_data.get_max_height_hash()?) {
    match e {
        SqliteClientError::BackendError(Error::InvalidChain(lower_bound, _)) => {
            // a) Pick a height to rewind to.
            //
            // This might be informed by some external chain reorg information, or
            // heuristics such as the platform, available bandwidth, size of recent
            // CompactBlocks, etc.
            let rewind_height = lower_bound - 10;

            // b) Rewind scanned block information.
            db_data.rewind_to_height(rewind_height);

            // c) Delete cached blocks from rewind_height onwards.
            //
            // This does imply that assumed-valid blocks will be re-downloaded, but it
            // is also possible that in the intervening time, a chain reorg has
            // occurred that orphaned some of those blocks.

            // d) If there is some separate thread or service downloading
            // CompactBlocks, tell it to go back and download from rewind_height
            // onwards.
        }
        e => {
            // Handle or return other errors.
            return Err(e);
        }
    }
}

// 3) Scan (any remaining) cached blocks.
//
// At this point, the cache and scanned data are locally consistent (though not
// necessarily consistent with the latest chain tip - this would be discovered the
// next time this codepath is executed after new blocks are received).
scan_cached_blocks(&network, &db_cache, &mut db_data, None)

Functions

scan_cached_blocks

Scans at most limit new blocks added to the cache for any transactions received by the tracked accounts.

validate_chain

Checks that the scanned blocks in the data database, when combined with the recent CompactBlocks in the cache database, form a valid chain.