Version: next

Requesting an order

This page is part of the typescript tutorial for creating your first COMIT-app, that builds two simple command-line application using the COMIT protocol to execute a Bitcoin to Ethereum atomic swap locally on your machine.

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In this section we focus on the taker side and work on taker.ts

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It is assumed that the maker application is finished at this stage, and running in a separate terminal.

In this section we fetch the order provided by a maker and check the rate.

Taker requests an Order

Similar to the maker, the comit-sdk provides provides a negotiation class for the taker as well, the TakerNegotiator.

Knowing where to fetch order the taker can now initialise the TakerNegotiator. Similar to the maker he also has to provide his ComitClient (initialised with the actor) for swap execution. Additionally he has to provide the URL of the maker's order service. The maker must share this information with the taker through some channel (e.g. Telegram group).

const takerNegotiator = new TakerNegotiator(
    taker.comitClient,
    "http://localhost:2318/"
);

The taker can now request an order from the maker by defining a filter criteria. The criteria defines what the taker would like to trade.

The taker wants to receive one bitcoin, which he is willing to sel for ether at a minimum rate of 0.001, hence he creates his criteria accordingly:

const criteria = {
    buy: {
        ledger: "bitcoin",
        asset: "bitcoin",
        minNominalAmount: "1",
    },
    sell: {
        ledger: "ethereum",
        asset: "ether",
    },
    minRate: 0.001,
};

This is needed, because the taker might not know what the maker has to offer and if it is still available. In a more advanced implementation such kind of functionality would be provided by an orderbook.

With the criteria the taker can now request an order from the maker:

const order = await takerNegotiator.getOrder(criteria);

Note that TakerOrder order returned by the TakerNegotiator is specific to the taker. It combines the maker's order, specified through the Order interface, the taker's criteria and provides a take function for the taker.

Let's log the rate offered by the maker:

console.log("Rate offered: ", order.getOfferedRate().toString());

Summary

At this stage your taker application should look similar to this:

import * as dotenv from "dotenv";
import * as os from "os";
import * as path from "path";
import {createActor, EthereumWallet, InMemoryBitcoinWallet, TakerNegotiator} from "comit-sdk";
import { formatEther } from "ethers/utils";

(async function main() {
    console.log("COMIT Taker app");

    const configPath = path.join(os.homedir(), ".create-comit-app", "env");
    dotenv.config({path: configPath});

    const bitcoinWallet = await InMemoryBitcoinWallet.newInstance(
        "regtest",
        process.env.BITCOIN_P2P_URI!,
        process.env[`BITCOIN_HD_KEY_${1}`]!
    );
    // Waiting for the Bitcoin wallet to read the balance
    await new Promise(r => setTimeout(r, 1000));

    const ethereumWallet = new EthereumWallet(
        process.env.ETHEREUM_NODE_HTTP_URL!,
        process.env[`ETHEREUM_KEY_${1}`]!
    );

    let taker = await createActor(
        bitcoinWallet,
        ethereumWallet,
        process.env[`HTTP_URL_CND_${1}`]!
    );

    console.log(
        "[Taker] Bitcoin balance: %f, Ether balance: %f",
        (await taker.bitcoinWallet.getBalance()).toFixed(2),
        parseFloat(
            formatEther(await taker.ethereumWallet.getBalance())
        ).toFixed(2)
    );

    const makerNegotiatorUrl = "http://localhost:2318/";

    const takerNegotiator = new TakerNegotiator(
        taker.comitClient,
        makerNegotiatorUrl
    );

    const criteria = {
        buy: {
            ledger: "bitcoin",
            asset: "bitcoin",
            minNominalAmount: "1",
        },
        sell: {
            ledger: "ethereum",
            asset: "ether",
        },
        minRate: 0.001,
    };

    const order = await takerNegotiator.getOrder(criteria);

    console.log("Rate offered: ", order.getOfferedRate().toString());

    // TODO: Execute the order by swapping the assets.

    process.exit();
})();

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In order to properly retrieve an order at the taker side, the maker application has to run at this stage! If your maker app is not running you can start it with yarn maker in a separate terminal.

Ensure that your maker app is running and then start the taker app with yarn taker - it should print:

yarn run v1.22.0
$ ts-node ./src/taker.ts
COMIT Taker app
[Taker] Bitcoin balance: 10, Ether balance: 1000
Rate offered:  0.02
✨  Done in 6.64s.

Since the taker only requests the offer and prints the rate, the swap execution is not yet triggered. Let's move on to the taker taking the order and triggering the swap execution!

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#Taker requests an Order

#Summary

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Taker requests an Order

Summary