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Configure a chain to use proof-of-work

The basic-pow node demonstrates how to add a custom consensus engine to a Substrate-based blockchain. In this example, the node uses a minimal proof-of-work consensus engine to reach agreement over the blockchain. This guide introduces a few core principles for working with consensus engines.

Use cases

  • Launch a chain that uses a proof-of-work consensus engine.
  • Upgrade a chain from an authority-based consensus engine to a proof-of-work consensus engine.

Steps preview

  1. Define a full node that uses proof-of-work consensus.
  2. Create an import queue for data providers.
  3. Define the proposer and worker functions.
  4. Define a light client service.

Define a full node using scconsensuspow and sc_service

In src/service.rs, make a function called new_full that defines PartialComponents and PowBlockImport:

let pow_block_import = sc_consensus_pow::PowBlockImport::new(
  client.clone(),
  client.clone(),
  sha3pow::MinimalSha3Algorithm,
  0,                              // check inherents starting at block 0
  select_chain.clone(),
  inherent_data_providers.clone(),
  can_author_with,
);

let import_queue = sc_consensus_pow::import_queue(
  Box::new(pow_block_import.clone()),
  None,
  sha3pow::MinimalSha3Algorithm,  // provide it with references to our client
  inherent_data_providers.clone(),
  &task_manager.spawn_handle(),
  config.prometheus_registry(),
)?;

Create an import queue

Define your node's inherents by using InherentDataProviders in a function that defines the providers of your POW system:

pub fn build_inherent_data_providers() -> Result<InherentDataProviders, ServiceError> {
  let providers = InherentDataProviders::new();

  providers
    .register_provider(sp_timestamp::InherentDataProvider)
    .map_err(Into::into)
    .map_err(sp_consensus::error::Error::InherentData)?;

    Ok(providers)
}

Define the proposer and worker

In the new_full function, define proposer:

let proposer = sc_basic_authorship::ProposerFactory::new(
    task_manager.spawn_handle(),
    client.clone(),
    transaction_pool,
    prometheus_registry.as_ref(),
);

let (_worker, worker_task) = sc_consensus_pow::start_mining_worker(
    Box::new(pow_block_import),
    client,
    select_chain,
    MinimalSha3Algorithm,
    proposer,
    network.clone(),
    None,
    inherent_data_providers,
    // time to wait for a new block before starting to mine a new one
    Duration::from_secs(10),
    // how long to take to actually build the block (i.e. executing extrinsics)
    Duration::from_secs(10),
    can_author_with,
);

Let the task manager spawn it:

task_manager
    .spawn_essential_handle()
    .spawn_blocking("pow", worker_task);

Examples

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