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https://github.com/status-im/nim-json-rpc

Nim library for implementing JSON-RPC clients and servers
https://github.com/status-im/nim-json-rpc

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Nim library for implementing JSON-RPC clients and servers

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# json-rpc



[![License: Apache](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://opensource.org/licenses/Apache-2.0)

[![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](https://opensource.org/licenses/MIT)

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Json-Rpc is a library designed to provide an easier interface for working with remote procedure calls.



# Usage



```nim

# In your nimble file

requires "json_rpc"

```



# Introduction



Json-Rpc is a library for routing JSON 2.0 format remote procedure calls over different transports.

It is designed to automatically generate marshalling and parameter checking code based on the RPC parameter types.



## Routing



Remote procedure calls are created using the `rpc` macro on an instance of `RpcRouter`.



`rpc` allows you to provide a list of native Nim type parameters and a return type, generates marshalling to and from json for you, so you can concentrate on using native Nim types for your call.



Routing is then performed by the `route` procedure.



When an error occurs, the `error` is populated, otherwise `result` will be populated.



### `rpc` Parameters



`path`: The string to match for the `method`.



`body`: The parameters and code to execute for this call.



### Example



Here's a simple example:



```nim

import

  json_rpc/rpcserver



var router = RpcRouter.init()



router.rpc("hello") do():

  result = %"Hello"

```



As no return type was specified in this example, `result` defaults to the `JsonNode` type.

A JSON string is returned by passing a string though the `JrpcConv` converter powered by [nim-json-serialization](https://github.com/status-im/nim-json-serialization).



The `body` parameters can be defined by using [do notation](https://nim-lang.org/docs/manual.html#procedures-do-notation).

This allows full Nim types to be used as RPC parameters.



Here we pass a string to an RPC and return a string.



```nim

router.rpc("hello") do(input: string) -> string:

  result = "Hello " & input

```



Json-Rpc will recursively parse the Nim types in order to produce marshalling code.

This marshalling code uses the types to check the incoming JSON fields to ensure they exist and are of the correct kind.



The return type then performs the opposite process, converting Nim types to Json for transport.



Here is a more complex parameter example:



```nim

import

  json_rpc/rpcserver,

  json_rpc/jsonmarshal



type

  HeaderKind = enum hkOne, hkTwo, hkThree



  Header = object

    kind: HeaderKind

    size: int64



  DataBlob = object

    items: seq[byte]

    headers: array[3, Header]



  MyObject = object

    data: DataBlob

    name: string



Header.useDefaultSerializationIn JrpcConv

DataBlob.useDefaultSerializationIn JrpcConv

MyObject.useDefaultSerializationIn JrpcConv



router.rpc("updateData") do(myObj: MyObject, newData: DataBlob) -> DataBlob:

  if myObj.name == "old":

    result = myObj.data

  else:

    result = newData

```



Behind the scenes, all RPC calls take parameters through `RequestParamsRx` structure.

At runtime, the json is checked to ensure that it contains the correct number and type of your parameters to match the `rpc` definition.



Compiling with `-d:nimDumpRpcs` will show the output code for the RPC call. To see the output of the `async` generation, add `-d:nimDumpAsync`.



### Special type :  `Option[T] `



Option[T] is a special type indicating that parameter may have value or not.

* If optional parameters located in the middle of parameters list, you set it to `null` to tell the server that it has no value.

* If optional parameters located at the end of parameter list and there are no more mandatory parameters after that, those optional parameters can be omitted altogether.



```Nim

# d can be omitted, b should use null to indicate it has no value

router.rpc("updateData") do(a: int, b: Option[int], c: string, d: Option[T]):

  if b.isSome:

    # do something

  else:

    # do something else

```



* If Option[T] used as return type, it also denotes the returned value might not available.



```Nim

router.rpc("getData") do(name: string) -> Option[int]:

  if name == "monkey":

    result = some(4)

```



* If Option[T] used as field type of an object, it also tell us that field might be present or not, and the rpc mechanism will automatically set it to some value if it available.



```Nim

type

  MyOptional = object

    maybeInt: Option[int]

```



## Marshalling



Note that `array` parameters are explicitly checked for length, and will return an error node if the length differs from their declaration size.



If you wish to support custom types in a particular way, you can provide matching `readValue` and `writeValue` procedures.

The custom serializer you write must be using `JrpcConv` flavor.



### `readValue`



This takes a Json type and returns the Nim type.



#### Parameters



`r: var JsonReader[JrpcConv]`: The current JsonReader with JrpcConv flavor.



`val: var MyInt`: Deserialized value.



#### Example



```nim

proc readValue*(r: var JsonReader[JrpcConv], val: var MyInt)

      {.gcsafe, raises: [IOError, JsonReaderError].} =

  let intVal = r.parseInt(int)

  val = MyInt(intVal)

```



### `writeValue`



This is the standard way to provide translations from a Nim type to Json.



#### Parameters



`w: var JsonWriter[JrpcConv]`: The current JsonWriter with JrpcConv flavor.



`val: MyInt`: The value you want to convert into Json.



#### Example



```nim

proc writeValue*(w: var JsonWriter[JrpcConv], val: MyInt)

      {.gcsafe, raises: [IOError].} =

  w.writeValue val.int

```



## JSON Format



The router expects either a Json document with the following structure:



```json

{

  "id": Int or String,

  "jsonrpc": "2.0",

  "method": String,

  "params": Array or Object

}



```



If params is an Array, it is a positional parameters. If it is an Object then the rpc method will be called using named parameters.



Return values use the following node structure:



```json

{

  "id": Int Or String,

  "jsonrpc": "2.0",

  "result": Json document,

  "error": Json document

}

```



## Performing a route



To call and RPC through the router, use the `route` procedure.



There are three variants of `route`.



Note that once invoked all RPC calls are error trapped and any exceptions raised are passed back with the error message encoded as a `Json document`.



### `route` by string



This `route` variant will handle all the conversion of `string` to `Json document` and check the format and type of the input data.



#### Parameters



`router: RpcRouter`: The router object that contains the RPCs.



`data: string`: A string ready to be processed into a `Json document`.



#### Returns



`Future[string]`: This will be the stringified JSON response, which can be the JSON RPC result or a JSON wrapped error.



### `route` by `Json document`



This variant allows simplified processing if you already have a `Json document`. However if the required fields are not present within `data`, exceptions will be raised.



#### Parameters



`router: RpcRouter`: The router object that contains the RPCs.



`req: RequestTx`: A pre-processed `Json document` that matches the expected format as defined above.



#### Returns



`Future[ResponseTx]`: The JSON RPC result or a JSON wrapped error.



### `tryRoute`



This `route` variant allows you to invoke a call if possible, without raising an exception.



#### Parameters



`router: RpcRouter`: The router object that contains the RPCs.



`data: JsonString`: A raw `Json document` that matches the expected format as defined above.



`fut: var Future[JsonString]`: The stringified JSON RPC result or a JSON wrapped error.



#### Returns



`Result[void, string]` `isOk` if the `method` field provided in `data` matches an available route. Returns `isErr` when the `method` cannot be found, or if `method` or `params` field cannot be found within `data`.



To see the result of a call, we need to provide Json in the expected format.

Here's an example of how that looks by manually creating the JSON. Later we will see the helper utilities that make this easier.



```nim

let call = %*{

  "id": %1,

  "jsonrpc": %"2.0",

  "method": %"hello",

  "params": %["Terry"]

  }

# route the call we defined earlier

let localResult = waitFor router.route(call)



echo localResult

# We should see something like this

#   {"jsonrpc":"2.0","id":1,"result":"Hello Terry"}

```



# Server



In order to make routing useful, RPCs must be invoked and transmitted over a transport.



The `RpcServer` type is given as a simple inheritable wrapper/container that simplifies designing your own transport layers using the `router` field.



## Server Transports



Currently there are plans for the following transports to be implemented:



* [x] Sockets

* [x] HTTP

* [ ] IPC

* [x] Websockets



Transport specific server need only call the `route` procedure using a string fetched from the transport in order to invoke the requested RPC.



## Server example



This example uses the socket transport defined in `socket.nim`.

Once executed, the "hello" RPC will be available to a socket based client.



```nim

import json_rpc/rpcserver



# Create a socket server for transport

var srv = newRpcSocketServer("localhost", Port(8585))



# srv.rpc is a shortcut for srv.router.rpc

srv.rpc("hello") do(input: string) -> string:

  result = "Hello " & input



srv.start()

runForever()

```



# Client



Json-Rpc also comes with a client implementation, built to provide a framework for transports to work with.



To simplify demonstration, we will use the socket transport defined in `socketclient.nim`.



Below is the most basic way to use a remote call on the client.

Here we manually supply the name and json parameters for the call.



The `call` procedure takes care of the basic format of the JSON to send to the server.

However you still need to provide `params` as a `JsonNode` or `RequestParamsTx`, which must exactly match the parameters defined in the equivalent `rpc` definition.



```nim

import json_rpc/[rpcclient, rpcserver], chronos, json



var

  server = newRpcSocketServer("localhost", Port(8545))

  client = newRpcSocketClient()



server.start



server.rpc("hello") do(input: string) -> string:

  result = "Hello " & input



waitFor client.connect("localhost", Port(8545))



let response = waitFor client.call("hello", %[%"Daisy"])



# the call returns a `JsonString` type which contains the result

echo response

```



### `createRpcSigs`



To make things more readable and allow better static checking client side, Json-Rpc supports generating wrappers for client RPCs using `createRpcSigs`.



This macro takes a type name and the path of a file containing forward declarations of procedures that you wish to convert to client RPCs. The transformation generates procedures that match the forward declarations provided, plus a `client` parameter in the specified type.



Because the signatures are parsed at compile time, the file will be error checked and you can use import to share common types between your client and server.



#### Parameters



`clientType`: This is the type you want to pass to your generated calls. Usually this would be a transport specific descendant from `RpcClient`.



`path`: The path to the Nim module that contains the RPC header signatures.



#### Variants of createRpcSigs

  - `createRpcSigsFromString`, generate rpc wrapper from string instead load it from file.

  - `createSingleRpcSig`, generate rpc wrapper from single Nim proc signature, with alias. e.g. calling same rpc method using different return type.

  - `createRpcSigsFromNim`, generate rpc wrapper from a list Nim proc signature, without loading any file.



#### Example



For example, to support this remote call:



```nim

server.rpc("bmi") do(height, weight: float) -> float:

  result = (height * height) / weight

```



You can have the following in your rpc signature file:



```nim

proc bmi(height, weight: float): float

```



When parsed through `createRpcSigs`, you can call the RPC as if it were a normal procedure.

So instead of this:



```nim

let bmiIndex = await client.call("bmi", %[%120.5, %12.0])

```



You can use:



```nim

let bmiIndex = await client.bmi(120.5, 12.0)

```



Or you can use batch call to send multiple request at once to the server.



```Nim

let batch = client.prepareBatch()

batch.bmi(120.5, 12.0)

batch.bmi(120.5, 13.0)

batch.bmi(120.5, 14.0)

let res = await batch.send()



# But you need to manually process the response e.g. decode from JSON to

# your expected type because you can mix various rpc method call in one batch

# with various return type.

```



This allows you to leverage Nim's static type checking whilst also aiding readability and providing a unified location to declare client side RPC definitions.



## Working with client transports



Transport clients should provide a type that is inherited from `RpcClient` where they can store any transport related information.



Additionally, the following two procedures are useful:



* `Call`



  `self`: a descendant of `RpcClient`

  `name: string`: the method to be called

  `params: JsonNode`: The parameters to the RPC call

  Returning

    `Future[JsonString]`: A wrapper for the result `Json document` and a flag to indicate if this contains an error.



Note: Although `call` isn't necessary for a client to function, it allows RPC signatures to be used by the `createRpcSigs`.



* `Connect`



  `client`: a descendant of `RpcClient`

  Returning

    `FutureBase`: The base future returned when a procedure is annoted with `{.async.}`



### `processMessage`



To simplify and unify processing within the client, the `processMessage` procedure can be used to perform conversion and error checking from the received string originating from the transport to the `Json document` representation that is passed to the RPC.



After a RPC returns, this procedure then completes the futures set by `call` invocations using the `id` field of the processed `Json document` from `line`.



#### Parameters



`self`: a client type descended from `RpcClient`



`line: string`: a string that contains the JSON to be processed



# Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.



Please make sure to update tests as appropriate.



## License



Licensed and distributed under either of



* MIT license: [LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT



or



* Apache License, Version 2.0, ([LICENSE-APACHEv2](LICENSE-APACHEv2) or http://www.apache.org/licenses/LICENSE-2.0)



at your option. This file may not be copied, modified, or distributed except according to those terms.