jsonrpc2.js

/*
 * JSON-RPC 2.0 implementation as per http://www.jsonrpc.org/specification.
 * License: MIT (https://opensource.org/licenses/MIT)
 * Author: Marco Quinten <splittydev@gmail.com>
 */

const debug = require('debug')('json-rpc');

// List of public API endpoints
var exposed = [];

// JSON-RPC 2.0 error codes
const JsonRpcErrors = {

    // Official response codes
    ParseError:     -32700,
    InternalError:  -32603,
    InvalidParams:  -32602,
    MethodNotFound: -32601,
    InvalidRequest: -32600,

    // Custom response codes
    RuntimeError:   -32001,
    ServerError:    -32000,
};

/**
 * Test if a JSON-RPC 2.0 object is a notification.
 * Notifications do not allow for replies.
 * 
 * @param {any} json_req The JSON-RPC 2.0 object.
 * @returns Whether the JSON-RPC 2.0 object is a notification.
 */
function json_rpc_is_notification(json_req) {
    return json_req.id === void 0;
}

/**
 * Send a JSON-RPC 2.0 response.
 * No additional checks are done.
 * 
 * @param {any} json_resp The JSON-RPC 2.0 response.
 * @param {any} send_callback The send function.
 */
function json_rpc_send_raw(json_resp, send_callback) {

    try {
        // Try sending the response
        send_callback(json_resp);
    } catch (e) {
        // Log errors to the console
        debug(`Error: ${e.message}`);
    }
}

/**
 * Create and send a JSON-RPC 2.0 result.
 * Checks for notification requests are done.
 * 
 * @param {any} json_req The JSON-RPC 2.0 request.
 * @param {any} result The result to be sent.
 * @param {any} send_callback The send function.
 */
function json_rpc_send_result(json_req, result, send_callback) {

    // Bail out if the JSON-RPC 2.0 object is a notification
    if (json_rpc_is_notification(json_req)) {
        return;
    }

    // Craft the response
    const json_resp = JSON.stringify({
        "jsonrpc": "2.0",
        "result": result,
        "id": json_req.id,
    });

    // Send the response
    json_rpc_send_raw(json_resp, send_callback);
}

/**
 * Create and send a JSON-RPC 2.0 error.
 * Checks for notification requests are done.
 * 
 * @param {any} json_req The JSON-RPC 2.0 request.
 * @param {any} code The error code.
 * @param {any} message The error message.
 * @param {any=} error The error object.
 */
function json_rpc_send_error(json_req, code, message, error) {

    // Bail out if the JSON-RPC 2.0 object is a notification
    if (json_rpc_is_notification(json_req)) {
        return;
    }

    // Craft the response
    const json_resp = JSON.stringify({
        "jsonrpc": "2.0",
        "error": {
            "code": code,
            "message": message,
            "data": error || [],
        },
        "id": json_req.id,
    });

    // Send the response
    json_rpc_send_raw(json_resp, send_callback);
}

/**
 * Turn a function into a valid API endpoint.
 * 
 * @param {any} func The function.
 * @returns The wrapped function.
 */
function json_rpc_wrap(func) {
    return (json_req, send_callback) => {

        // Construct RPC object
        const rpc = {

            // Send result
            send: (result) => {
                json_rpc_send_result(json_req, result, send_callback);
            },
        };

        try {
            // Try invoking the function
            func(rpc, json_req.params);
        } catch (e) {
            // Handle errors by sending back an error response
            json_rpc_send_error(json_req, JsonRpcErrors.RuntimeError, e.message, e);
        }
    };
}

/**
 * Test a JSON object for JSON-RPC 2.0 compliance.
 * 
 * @param {any} json The JSON object to be validated.
 * @returns Whether the specified JSON object is a valid JSON-RPC 2.0 request.
 */
function json_rpc_validate(json) {

    // Check header
    if (json.jsonrpc !== '2.0') {
        debug('Field `jsonrpc` MUST be exactly "2.0"!');
        return false;
    }

    // Check method
    if (json.method.constructor !== String) {
        debug('Field `method` MUST be a String!');
        return false;
    }

    // Check id
    if (json.id !== void 0 // id can be omitted
        && json.id.constructor !== String
        && json.id.constructor !== Number
        && json.id.constructor !== null) {
        debug('Field `id` MUST be of type String, Number, or null!');
        return false;
    } else if (json.id === null) {
        debug('Field `id` SHOULD NOT be null!');
    } else if (json.id.constructor === Number && (Math.trunc(json.id) !== json.id)) {
        debug('Field `id` SHOULD NOT contain a fractional part!');
    }

    // All good!
    return true;
}

/**
 * Call a local API endpoint.
 * 
 * @param {any} plain_json The plain-text request.
 * @param {any} send_callback The send function.
 * @returns Whether the JSON-RPC 2.0 call succeeded.
 */
function json_rpc_call(plain_json, send_callback) {

    // Parse plain-text request
    const json_req = (() => {
        try {
            return JSON.parse(plain_json);
        } catch (e) {
            debug('Malformed JSON!');
        }
    })();

    // Validate request
    if (!json_rpc_validate(json_req)) {
        debug('Malformed JSON-RPC 2.0 request!');
        json_rpc_send_error(json_req, JsonRpcErrors.InvalidRequest, 'Invalid format!');
        return false;
    }

    // Find local endpoint
    const endpoint = exposed.find(func => {
        return func.name === json_req.method;
    });

    // Check if the desired endpoint was found
    if (endpoint === void 0) {
        debug(`Method not found: ${json_req.method}`);
        json_rpc_send_error(json_req, JsonRpcErrors.MethodNotFound);
        return false;
    }

    debug(`<- ${json_req.method}`);

    // Invoke local endpoint
    endpoint.call(json_req, send_callback);

    // All good!
    return true;
}

/**
 * Expose a function as a local API endpoint.
 * 
 * @param {any} name The name of the function on the remote end.
 * @param {any} func The function on the local end.
 */
function json_rpc_expose(name, func) {

    // Whitelist the endpoint
    exposed.push({
        name: name,
        call: json_rpc_wrap(func),
    });
}

module.exports = {
    call: json_rpc_call,
    expose: json_rpc_expose,
};