import {
  JsonRpcController,
  JsonRpcMethod,
  IJsonRpcId,
  IJsonRpcParams
} from 'nestjs-json-rpc'

@JsonRpcController('/jsonrpc/endpoint')
export class SomeJsonRpcController {
  @JsonRpcMethod('some-method')
  doSomething(@JsonRpcId() id: IJsonRpcId, @JsonRpcParams() params: IJsonRpcParams) {
    const {foo} = params
    
    if (foo === 'bar') {
      return new JsonRpcError(-100, '"foo" param should not be equal "bar"')
    }
    
    return 'ok'
  }
}

// App.ts
@Module({
  imports: [...],
  controllers: [SomeJsonRpcController],
  providers: [...],
})
export class AppModule {}

import {
  JsonRpcMiddleware,
  JsonRpcMethod,
  IJsonRpcId,
  IJsonRpcParams
} from 'expressjs-json-rpc'

@JsonRpcMiddleware()
export class SomeJsonRpcMware {
  @JsonRpcMethod('some-method')
  doSomething(@JsonRpcId() id: IJsonRpcId, @JsonRpcParams() params: IJsonRpcParams) {
    const {foo} = params
    
    if (foo === 'bar') {
      return new JsonRpcError(-100, '"foo" param should not be equal "bar"')
    }
    
    return 'ok'
  }
} 

const jsonRpcMware = new SomeJsonRpcMware().middleware

app.use('/rpc', jsonRpcMware)