Json-Rpc is a library designed to provide an easier interface for working with remote procedure calls.
# In your nimble file
requires "json_rpc"
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.
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.
path
: The string to match for the method
.
body
: The parameters and code to execute for this call.
Here's a simple example:
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.
The body
parameters can be defined by using 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.
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:
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
.
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.
# 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.
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.
type
MyOptional = object
maybeInt: Option[int]
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.
This takes a Json type and returns the Nim type.
r: var JsonReader[JrpcConv]
: The current JsonReader with JrpcConv flavor.
val: var MyInt
: Deserialized value.
proc readValue*(r: var JsonReader[JrpcConv], val: var MyInt)
{.gcsafe, raises: [IOError, JsonReaderError].} =
let intVal = r.parseInt(int)
val = MyInt(intVal)
This is the standard way to provide translations from a Nim type to Json.
w: var JsonWriter[JrpcConv]
: The current JsonWriter with JrpcConv flavor.
val: MyInt
: The value you want to convert into Json.
proc writeValue*(w: var JsonWriter[JrpcConv], val: MyInt)
{.gcsafe, raises: [IOError].} =
w.writeValue val.int
The router expects either a Json document with the following structure:
{
"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:
{
"id": Int Or String,
"jsonrpc": "2.0",
"result": Json document,
"error": Json document
}
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
.
This route
variant will handle all the conversion of string
to Json document
and check the format and type of the input data.
router: RpcRouter
: The router object that contains the RPCs.
data: string
: A string ready to be processed into a Json document
.
Future[string]
: This will be the stringified JSON response, which can be the JSON RPC result or a JSON wrapped error.
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.
router: RpcRouter
: The router object that contains the RPCs.
req: RequestTx
: A pre-processed Json document
that matches the expected format as defined above.
Future[ResponseTx]
: The JSON RPC result or a JSON wrapped error.
This route
variant allows you to invoke a call if possible, without raising an exception.
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.
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.
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"}
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.
Currently there are plans for the following transports to be implemented:
- Sockets
- HTTP
- IPC
- Websockets
Transport specific server need only call the route
procedure using a string fetched from the transport in order to invoke the requested RPC.
This example uses the socket transport defined in socket.nim
.
Once executed, the "hello" RPC will be available to a socket based client.
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()
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.
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
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.
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.
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.
For example, to support this remote call:
server.rpc("bmi") do(height, weight: float) -> float:
result = (height * height) / weight
You can have the following in your rpc signature file:
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:
let bmiIndex = await client.call("bmi", %[%120.5, %12.0])
You can use:
let bmiIndex = await client.bmi(120.5, 12.0)
Or you can use batch call to send multiple request at once to the server.
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.
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 ofRpcClient
name: string
: the method to be calledparams: JsonNode
: The parameters to the RPC call ReturningFuture[JsonString]
: A wrapper for the resultJson 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 ofRpcClient
ReturningFutureBase
: The base future returned when a procedure is annoted with{.async.}
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
.
self
: a client type descended from RpcClient
line: string
: a string that contains the JSON to be processed
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.
Licensed and distributed under either of
- MIT license: LICENSE-MIT or https://opensource.org/licenses/MIT
or
- Apache License, Version 2.0, (LICENSE-APACHEv2 or https://www.apache.org/licenses/LICENSE-2.0)
at your option. This file may not be copied, modified, or distributed except according to those terms.