How do I include a new rpc that uses a NetworkWorker in the node-template?

Question

The node-template says its service.rs is a specialisation of that on the substrate master branch. Hence, it's sort of hard to relate the two. Nonetheless, I'd like to expose an RPC endpoint that's accessible to both off-chain workers and (implicitly) the polkadotjs API, such as the system_peers endpoint that requires the NetworkWorker. But this is hidden in the node-template implementation. how/where would I look to obtain an instance of it or an equivalent struct in the node-template?

Please note that I'm unfamiliar with asynchronous rust, and implementing custom RPCs, hence the wording might be a bit off, But I'm open to good resources for practical uses of both.

Thanks in advance!

Answer 1

To add a new RPC to the Substrate Node Template, you should look at the rpc.rs file included with it that contains an example and docs for adding a new RPC:

/node/src/rpc.rs

/// Instantiate all full RPC extensions.
pub fn create_full<C, P>(deps: FullDeps<C, P>) -> jsonrpc_core::IoHandler<sc_rpc::Metadata>
where
    C: ProvideRuntimeApi<Block>,
    C: HeaderBackend<Block> + HeaderMetadata<Block, Error = BlockChainError> + 'static,
    C: Send + Sync + 'static,
    C::Api: substrate_frame_rpc_system::AccountNonceApi<Block, AccountId, Index>,
    C::Api: pallet_transaction_payment_rpc::TransactionPaymentRuntimeApi<Block, Balance>,
    C::Api: BlockBuilder<Block>,
    P: TransactionPool + 'static,
{
    use pallet_transaction_payment_rpc::{TransactionPayment, TransactionPaymentApi};
    use substrate_frame_rpc_system::{FullSystem, SystemApi};

    let mut io = jsonrpc_core::IoHandler::default();
    let FullDeps { client, pool, deny_unsafe } = deps;

    io.extend_with(SystemApi::to_delegate(FullSystem::new(client.clone(), pool, deny_unsafe)));

    io.extend_with(TransactionPaymentApi::to_delegate(TransactionPayment::new(client.clone())));

    // Extend this RPC with a custom API by using the following syntax.
    // `YourRpcStruct` should have a reference to a client, which is needed
    // to call into the runtime.
    // `io.extend_with(YourRpcTrait::to_delegate(YourRpcStruct::new(ReferenceToClient, ...)));`

    io
}

As for specifically implementing the NetworkWorker into your node, you should take a look at the implementation in the main Substrate Node, and pull that in. Otherwise, you can open a new issue, and ask a developer to include it into the node-template for you.