index.js

const app = require("express")();
const proxy = require("express-http-proxy");
const { target, apiKey, port, whitelist } = require("./config");
const isNodeSynced = require("./lib/is-node-synced");
const cors = require("cors");

function tryParseJSON (rawJson) {
    try {
        const object = JSON.parse(rawJson);
        if (object && typeof object === "object")
            return object;
    }
    catch (e) {}
    return false;
};

app.use(cors());

app.get('/health', (req, res) => {
    return isNodeSynced()
      .then(result => res.send(result))
      .catch(() => res.send({ latestBlock: 0, synced: false }))
});

app.use(proxy(target, {

    proxyReqBodyDecorator: (bodyContent) => {
        const body = tryParseJSON(bodyContent);
        if (body && whitelist.includes(body.method)) {
            return {
                ...body,
                key: apiKey,
            };
        }
        return "";
    },

}));

app.listen(port);