feat: initialize Kurdistan SDK - independent fork of Polkadot SDK

2025-12-13 15:44:15 +03:00
commit e4778b4576
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+//! # Custom RPC do's and don'ts
+//!
+//! **TLDR:** Don't create new custom RPCs. Instead, rely on custom Runtime APIs, combined with
+//! `state_call`.
+//!
+//! ## Background
+//!
+//! Pezkuwi-SDK offers the ability to query and subscribe storages directly. However what it does
+//! not have is [view functions](https://github.com/pezkuwichain/pezkuwi-sdk/issues/101). This is an
+//! essential feature to avoid duplicated logic between runtime and the client SDK. Custom RPC was
+//! used as a solution. It allow the RPC node to expose new RPCs that clients can be used to query
+//! computed properties.
+//!
+//! ## Problems with Custom RPC
+//!
+//! Unfortunately, custom RPC comes with many problems. To list a few:
+//!
+//! - It is offchain logic executed by the RPC node and therefore the client has to trust the RPC
+//!   node.
+//! - To upgrade or add a new RPC logic, the RPC node has to be upgraded. This can cause significant
+//!   trouble when the RPC infrastructure is decentralized as we will need to coordinate multiple
+//!   parties to upgrade the RPC nodes.
+//! - A lot of boilerplate code is required to add custom RPC.
+//! - It prevents dApps from using a light client or an alternative client.
+//! - It makes ecosystem tooling integration much more complicated. For example, dApps will not
+//!   be able to use [Chopsticks](https://github.com/AcalaNetwork/chopsticks) for testing as
+//!   Chopsticks will not have the custom RPC implementation.
+//! - Poorly implemented custom RPC can be a DoS vector.
+//!
+//! Hence, we should avoid custom RPC.
+//!
+//! ## Alternatives
+//!
+//! Generally, [`sc_rpc::state::StateBackend::call`] aka. `state_call` should be used instead of
+//! custom RPC.
+//!
+//! Usually, each custom RPC comes with a corresponding runtime API which implements the business
+//! logic. So instead of invoke the custom RPC, we can use `state_call` to invoke the runtime API
+//! directly. This is a trivial change on the dApp and no change on the runtime side. We may remove
+//! the custom RPC from the node side if wanted.
+//!
+//! There are some other cases that a simple runtime API is not enough. For example, implementation
+//! of Ethereum RPC requires an additional offchain database to index transactions. In this
+//! particular case, we can have the RPC implemented on another client.
+//!
+//! For example, the Acala EVM+ RPC are implemented by
+//! [eth-rpc-adapter](https://github.com/AcalaNetwork/bodhi.js/tree/master/packages/eth-rpc-adapter).
+//! Alternatively, the [Frontier](https://github.com/polkadot-evm/frontier) project  also provided
+//! Ethereum RPC compatibility directly in the node-side software.
+//!
+//! ## Create a new Runtime API
+//!
+//! For example, let's take a look at the process through which the account nonce can be queried
+//! through an RPC. First, a new runtime-api needs to be declared:
+#![doc = docify::embed!("../../substrate/frame/system/rpc/runtime-api/src/lib.rs", AccountNonceApi)]
+//!
+//! This API is implemented at the runtime level, always inside [`sp_api::impl_runtime_apis!`].
+//!
+//! As noted, this is already enough to make this API usable via `state_call`.
+//!
+//! ## Create a new custom RPC (Legacy)
+//!
+//! Should you wish to implement the legacy approach of exposing this runtime-api as a custom
+//! RPC-api, then a custom RPC server has to be defined.
+#![doc = docify::embed!("../../substrate/utils/frame/rpc/system/src/lib.rs", SystemApi)]
+//!
+//! ## Add a new RPC to the node (Legacy)
+//!
+//! Finally, this custom RPC needs to be integrated into the node side. This is usually done in a
+//! `rpc.rs` in a typical template, as follows:
+#![doc = docify::embed!("../../templates/minimal/node/src/rpc.rs", create_full)]
+//!
+//! ## Future
+//!
+//! - [XCQ](https://forum.polkadot.network/t/cross-consensus-query-language-xcq/7583) will be a good
+//! solution for most of the query needs.
+//! - [New JSON-RPC Specification](https://github.com/paritytech/json-rpc-interface-spec)