# JsonRpcCondition

The `JsonRpcCondition` is designed for access control decisions that rely on data from an external HTTPS JSON RPC endpoint following the [JSON RPC 2.0 specification](https://www.jsonrpc.org/specification).

The condition operates by sending an HTTPS `POST` request to a specified JSON RPC endpoint using a [`JSONPath`](https://goessner.net/articles/JsonPath/) query to extract relevant data from the response and comparing the extracted value to an expected result.

It is composed of the following properties:

* `endpoint`: the HTTPS URI for the JSON RPC endpoint that will be queried, e.g.`https://api.example.com`
* `method`: the JSON RPC method to be invoked
* `params`*(Optional)*: Parameters for the specified method, provided as either a dictionary or an array.
* `query`*(Optional)*: a `JSONPath` query used to extract specific data from the JSON response. The query is relative to the `result` entry included in the JSON response.
* [`authorizationToken`](/for-developers/taco-sdk/references/conditions/json-endpoint-conditions.md#authorization) *(Optional)*: A bearer token that will be included in the HTTPS `Authorization` header. It enables the use of endpoints that require OAuth/JWT authorization.
* `authorizationType` (Optional): If an `authorizationToken` is specified, the type specifies the request header information to specify. Can be `Bearer`, `Basic`, or `X-API-Key`.
* [`returnValueTest`](/for-developers/taco-sdk/references/conditions.md#returnvaluetest): the test to validate the value extracted by the JSONPath query.

**Error Handling**

* If the HTTPS response does not return a status code of `200`, the condition will fail automatically, and access will be denied.
* If the `JSONPath` query is provided but cannot properly extract the desired value, the condition will fail, resulting in access being denied.
* If an invalid `authorizationToken` is provided, the call to the API will fail, causing the condition to fail and access to be denied.

## **Use Cases**

Any JSON RPC 2.0 endpoint including:

* Requests to non-EVM blockchain JSON RPC endpoints e.g. Bitcoin, Solana. *(A separate non-EVM blockchain condition may be added if there is sufficient use in this area)*
* Oracle endpoints e.g. market data, prices

## Example

```typescript
import { conditions } from '@nucypher/taco';

const firstBookPrice = new conditions.base.jsonRpc.JsonRpcCondition({
  endpoint: 'https://math.example.com/',
  method: 'subtract',
  params: [42, 23],
  query: '$.mathresult',
  authorizationToken: ":authToken",
  returnValueTest: {
    comparator: "==",
    value: 19
  },
});
```

The JSON data for the HTTP POST request to the RPC endpoint will look like the following:

```json
{
    "jsonrpc": "2.0",
    "id":1,
    "method": "subtract",
    "params": [
        42,
        23
    ]
}
```

The condition would be satisfied if the JSON RPC endpoint returned something analogous to the following:

```json
{
    "jsonrpc": "2.0",
    "result": {
        "mathresult": 19
    },
    "id": 1
}
```

## Development References

* Client-side:
  * <https://github.com/nucypher/taco-web/pull/606>
* Server-side:
  * <https://github.com/nucypher/nucypher/pull/3571>


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