WIP: Add support for generating rpc.discover method

[Velnbur]

Description

This PR implements optional generation of rpc.discover method which returns OpenRPC specification from trait definition. For that open-rpc crate was forked to fix compatibility issues with official examples and to add some useful conversion functions (about that a little bit later).

This works by using utoipa::schema! and utoipa::ToSchema crate macros, that generate utoipa::openapi::Schema structure at runtime, which later converted to open_rpc::Schema and, with information from server trait definition, to open_rpc::ContentDescriptor.

With these information about each trait method, open_rpc::OpenRpc structure is constructed inside rpc.discover method at runtime. For now it's constructed on each rpc.discover call, but this can be improved by adding some lazy static variable.

Functionality

For example, you can take a look at examples/examples/rpc_discover.rs, run it:

cd examples && cargo run --example rpc_discover

then send request to server:

curl -X POST -H "Content-Type: application/json" http://127.0.0.1:8080 -d '{"jsonrpc": "2.0","id":"id", "method": "rpc.discover"}' | jq .result

Response

{
  "openrpc": "1.0.0-rc1",
  "info": {
    "title": "Rpc",
    "version": ""
  },
  "servers": [],
  "methods": [
    {
      "name": "foo",
      "description": "",
      "params": [
        {
          "name": "param_a",
          "required": true,
          "schema": {
            "type": "integer",
            "minimum": 0
          }
        },
        {
          "name": "param_b",
          "required": true,
          "schema": {
            "type": "string"
          }
        }
      ],
      "result": {
        "name": "return",
        "required": true,
        "schema": {
          "type": "integer",
          "minimum": 0
        }
      }
    },
    {
      "name": "add",
      "description": "",
      "params": [
        {
          "name": "request",
          "required": true,
          "schema": {
            "type": "object",
            "properties": {
              "a": {
                "type": "integer",
                "minimum": 0
              },
              "b": {
                "type": "integer",
                "minimum": 0
              }
            },
            "required": [
              "a",
              "b"
            ]
          }
        }
      ],
      "result": {
        "name": "return",
        "required": true,
        "schema": {
          "type": "object",
          "properties": {
            "sum": {
              "type": "integer",
              "minimum": 0
            }
          },
          "required": [
            "sum"
          ]
        }
      }
    },
    {
      "name": "calculate",
      "description": "",
      "params": [
        {
          "name": "args",
          "required": true,
          "schema": {
            "type": "array",
            "items": {
              "type": "integer"
            }
          }
        },
        {
          "name": "operation",
          "required": true,
          "schema": {
            "type": "string",
            "enum": [
              "add",
              "mul",
              "sub"
            ]
          }
        }
      ],
      "result": {
        "name": "return",
        "required": true,
        "schema": {
          "type": "integer"
        }
      }
    }
  ]
}

copy response, and introspect it, for example, using OpenRPC Playground.

[Velnbur]

Not sure what to do with open-rpc crate, as original author seems to abandon it, maybe it can be as part of the OpenRPC organization or jsonrpsee crates