RPC custom request/response

Question

Currently using Postman I can make requests to my node and get a response. The code below is a request:

{
 "jsonrpc":"2.0",
  "id":3,
  "method":"sumStorage_getSum",
   "params": ["4"]
}

and I get the following response:

{
"jsonrpc": "2.0",
"result": 8,
"id": 3

}

which is fine for simple things.

But I would like to make a custom request like this one:

{
 "jsonrpc":"2.0",
  "id":3,
  "method":"silly_double",
  "params": [{"id":4}]
}

and receive a response like this one:

{
"jsonrpc": "2.0",
"success": { "code": 200, "sum", 18 },
"id": 3

}

Do you have any examples of how can I do this? I did not find any examples.

Thank you

Answer 1

You have to change the code of your function to return a struct instead of a u32 value.

With the response you are looking for, the struct would be:

pub struct CustomResponse {
  code: u32,
  sum: u32,
}

In order to Serialize/Deserialize this struct for the RpcResponse you will have to add a library to do that.

Import it in your Cargo.toml file:

serde = "1.0.136"
serde_json = "1.0.85"

And include the decorator to your struct:

#[derive(serde::Deserialize, serde::Serialize)]
pub struct CustomResponse {
    code: u32,
    sum: u32,
}

The RPC's implementation has to be modified too for returning the new struct in the response.

Change the get_sum declaration to use the new struct.

#[rpc]
pub trait SumStorageApi<BlockHash> {
 #[rpc(name = "sumStorage_getSum")]
 fn get_sum(
     &self,
     at: Option<BlockHash>
 ) -> Result<CustomResponse>;
}

And finally change the implementation of the get_sum function from:

fn get_sum(
    &self,
    at: Option<<Block as BlockT>::Hash>
) -> Result<u32> {

    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.
        self.client.info().best_hash
    ));

    let runtime_api_result = api.get_sum(&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()),
    })
}

To:

fn get_sum(
    &self,
    at: Option<<Block as BlockT>::Hash>
) -> Result<CustomResponse> {

    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.
        self.client.info().best_hash
    ));

    let runtime_api_result = api.get_sum(&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()),
    });
    Ok(CustomResponse{ code: 200, sum: value.unwrap()})
}

When query this RPC call you should get something like it now:

 {
  "jsonrpc": "2.0",
  "result": {
      "code": 200,
      "sum": 18
  },
  "id": 3
 }