cardo-org.github.io/jsonrpc.qmd at main · cardo-org/cardo-org.github.io · GitHub

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---
title: JSON-RPC
---

Rembus fully supports the
[JSON_RPC 2.0 Specification](https://www.jsonrpc.org/specification)

## RPC Request

```{mermaid}
flowchart LR
  C(("JSON-RPC
  Client")) --> S((Julia Server))
  style C fill:green, color:white
  style S fill:blue, color:white
```


### Server 🔵 - Exposing a service

The following (Julia) server exposes a method `mymethod` over an HTTP endpoint:

```julia
using Rembus

function mymethod(;x, y, z) # expect to be called with keywords arguments
    return Dict(
        "x" => x,
        "y" => y,
        "z" => z,
        "op" => "x + y*z",
        "value" => x + y * z
    )
end

rb = component(http=9000)
expose(rb, mymethod)
wait(rb)
```

### JSON-RPC Client 🟢

When the server method requires keyword arguments, the JSON-RPC `params` field
must be an object with matching keys:

```bash
curl -X POST http://localhost:9000 \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "mymethod",
    "params": {"x": 1, "y": 2, "z": 3}
  }'
```

The server responds with a JSON object encoding the Julia `Dict` returned
by `mymethod`:

```json
{
  "id":1,
  "jsonrpc":"2.0",
  "result": {
    "x":1,
    "y":2,
    "z":3,
    "op":"x + y*z",
    "value":7
  }
}
```

## Sending Notifications

A JSON_RPC **Notification** is simply a Request object **without an** `id`
field.

In Rembus, notifications map naturally to **Pub/Sub messages**: any published
message is delivered to all subscribed components.

In this example, the topic is named `mymethod`.

### Server 🔵 - Subscribing to a topic

```julia
using Rembus

function mymethod(x, y, z)
    println("mymethod called with x=$x, y=$y, z=$z")
end

rb = component(http=9000)
subscribe(rb, mymethod)

# Declare readiness to receive messages from subscribed topics,
# in this case the topic mymethod.
reactive(rb)

# Start the event loop.
wait(rb)

```

### JSON-RPC Publisher 🟢

```bash
curl -X POST http://localhost:9000 \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "mymethod",
    "params": [1,2,3]
  }'
```

## Batch

To send multiple requests in a single call, the client may submit an array
of Request objects:

```bash
curl -X POST http://localhost:9000 \
  -H "Content-Type: application/json" \
  -d '[
    {
      "jsonrpc": "2.0",
      "method": "method1",
      "params": {"x": 1, "y": 2, "z": 3}
    },{
      "jsonrpc": "2.0",
      "method": "method2",
      "params": ["mystring", 1.0]
    }
  ]'

```