I am trying to implement custom rpc using the tutorial : https://substrate.recipes/custom-rpc.html, I successfully implemented silly rpc but getting error for runtime api rpc.

Here are my code: template/rpc/src/lib.rs

use jsonrpc_core::{Error as RpcError, ErrorCode, Result};
use jsonrpc_derive::rpc;
use sp_api::ProvideRuntimeApi;
use sp_blockchain::HeaderBackend;
use sp_runtime::{generic::BlockId, traits::Block as BlockT};
use std::sync::Arc;
use shivarthu_runtime_api::ShivarthuApi as ShivarthuRuntimeApi;

pub trait ShivarthuApi<BlockHash> {
    #[rpc(name= "shivarthu_helloWorld")]
    fn hello_world(&self, at: Option<BlockHash>) -> Result<u128>;

pub struct Shivarthu<C, M> {
    client: Arc<C>,
    _marker: std::marker::PhantomData<M>,

impl<C, M> Shivarthu<C, M> {
    pub fn new(client: Arc<C>) -> Self {
        Self {
            _marker: Default::default(),

impl<C, Block> ShivarthuApi<<Block as BlockT>::Hash> for Shivarthu<C, Block>
    Block: BlockT,
    C: Send + Sync + 'static,
    C: ProvideRuntimeApi<Block>,
    C: HeaderBackend<Block>,
    C::Api: ShivarthuRuntimeApi<Block>,
    fn hello_world(&self, at: Option<<Block as BlockT>::Hash>) -> Result<u128> {
        let api = self.client.runtime_api();
        let at = BlockId::hash(at.unwrap_or_else(||
            // If the block hash is not supplied assume the best block.

        let runtime_api_result = api.hello_world(&at);
        runtime_api_result.map_err(|e| RpcError {
            code: ErrorCode::ServerError(9876), // No real reason for this value
            message: "Something wrong".into(),
            data: Some(format!("{:?}", e).into()),

In node/src/rpc.rs


It gives error:

   |                    ---------------------------------------- required by a bound introduced by this call
58 |         shivarthu_rpc::Shivarthu::new(client),
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `shivarthu_runtime_api::ShivarthuApi<sp_runtime::generic::Block<sp_runtime::generic::Header<u32, BlakeTwo256>, OpaqueExtrinsic>>` is not implemented for `<C as ProvideRuntimeApi<sp_runtime::generic::Block<sp_runtime::generic::Header<u32, BlakeTwo256>, OpaqueExtrinsic>>>::Api`
   = note: required because of the requirements on the impl of `ShivarthuApi<H256>` for `Shivarthu<C, sp_runtime::generic::Block<sp_runtime::generic::Header<u32, BlakeTwo256>, OpaqueExtrinsic>>`
help: consider further restricting the associated type
36 |     P: TransactionPool + 'static, <C as ProvideRuntimeApi<sp_runtime::generic::Block<sp_runtime::generic::Header<u32, BlakeTwo256>, OpaqueExtrinsic>>>::Api: shivarthu_runtime_api::ShivarthuApi<sp_runtime::generic::Block<sp_runtime::generic::Header<u32, BlakeTwo256>, OpaqueExtrinsic>>

1 Answer 1


Ya got it,

The error was because of file node/src/rpc.rs

pub fn create_full<C, P>(deps: FullDeps<C, P>) -> jsonrpc_core::IoHandler<sc_rpc::Metadata>
    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>,
    C::Api: shivarthu_runtime_api::ShivarthuApi<Block>,
    P: TransactionPool + 'static,

I didn't put this line:

C::Api: shivarthu_runtime_api::ShivarthuApi<Block>,
  • 1
    I had the same issue and this solved my issue!
    – andresvsm
    Commented Apr 17, 2022 at 11:19

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