How to add a JSON RPC method

1. Choose a module that your method will be placed in.

• chain module is for reading or writing blockchain, including parcel queue.
• devel module is for utility functions to debug CodeChain

2. Modify rpc/src/v1/traits/<module name>.rs

chain_getBlockHash example (chain_getBlockHash usage example):

/// Gets the hash of the block with given number.
# [rpc(name = "chain_getBlockHash")]
fn get_block_hash(&self, u64) -> Result<Option<H256>>;

The above declaration is part of pub trait Chain. It creates the RPC endpoint to "chain_getBlockHash" which receives u64 parameter. All of the parameters must be the serde-Serializable. See files in src/rpc/v1/types/ directory.

3. Modify rpc/src/v1/impls/<module name>.rs

chain_getBlockHash example:

fn get_block_hash(&self, block_number: u64) -> Result<Option<H256>> {
    Ok(self.client.block_hash(BlockId::Number(block_number)))
}

The above implementation is part of impl Chain for ChainClient. ChainClient holds Client and Miner which are the structs for the blockchain and the parcel queue each.

The above shows chain_getBlockHash is implemented using block_hash function in Client.