GUIDES.md

#stellar-lib Guides

This file provides step-by-step walkthroughs for some of the most common usages of stellar-lib.

###Guides in this document:

1. Connecting to the Stellar network with Remote
2. Using Remote functions and Request objects
3. Submitting a payment to the network
   • A note on transaction fees
4. Submitting a trade offer to the network
5. Listening to the network

###Also see:

1. The stellar-lib README
2. The stellar-lib API Reference

##1. Connecting to the Stellar network with Remote

1. Get stellar-lib
2. Load the stellar-lib module into a Node.js file or webpage:

/* Loading stellar-lib with Node.js */
var Remote = require('stellar-lib').Remote;

/* Loading stellar-lib in a webpage */
// var Remote = stellar.Remote;

3. Create a new Remote and connect to the network:

var remote = new Remote({options});

remote.connect(function() {
  /* remote connected, use some remote functions here */
});

NOTE: See the API Reference for available Remote options 4. You're connected! Read on to see what to do now.

##2. Using Remote functions and Request objects

All Remote functions return a Request object.

A Request is an EventEmitter so you can listen for success or failure events -- or, instead, you can provide a callback to the Remote function.

Here is an example, using request_server_info(), of how Remote functions can be used with event listeners (the first code block) or with a callback (the second block):

• Using a Remote function with Request event listeners:

var request = remote.request_server_info();
request.on('success', function(res) {
  //handle success
});
request.on('error', function(err) {
  //handle error
});
request.request(); // this triggers the request if it has not already been sent to the server

• Using a Remote function with a callback:

remote.request_server_info(function(err, res) {
  if (err) {
    //handle error
  } else {
    //handle success
  }
});

NOTE: See the API Reference for available Remote functions

##3. Submitting a payment to the network

Submitting a payment transaction to the Stellar network involves connecting to a Remote, creating a transaction, signing it with the user's secret, and submitting it to the stellard server. Note that the Amount module is used to convert human-readable amounts like '1XRP' or '10.50USD' to the type of Amount object used by the Stellar network.

/* Loading stellar-lib Remote and Amount modules in Node.js */ 
var Remote = require('stellar-lib').Remote;
var Amount = require('stellar-lib').Amount;

/* Loading stellar-lib Remote and Amount modules in a webpage */
// var Remote = stellar.Remote;
// var Amount = stellar.Amount;

var MY_ADDRESS = 'rrrMyAddress';
var MY_SECRET  = 'secret';
var RECIPIENT  = 'rrrRecipient';
var AMOUNT     = Amount.from_human('1STR');

var remote = new Remote({ /* Remote options */ });

remote.connect(function() {
  remote.set_secret(MY_ADDRESS, MY_SECRET);

  var transaction = remote.transaction();

  transaction.payment({
    from: MY_ADDRESS, 
    to: RECIPIENT, 
    amount: AMOUNT
  });

  transaction.submit(function(err, res) {
    /* handle submission errors / success */
  });
});

###A note on transaction fees

A full description of network transaction fees can be found on the Stellar Wiki.

In short, transaction fees are very small amounts (on the order of ~10) of Stroop spent with every transaction. They are largely used to account for network load and prevent spam. With stellar-lib, transaction fees are calculated locally by default and the fee you are willing to pay is submitted along with your transaction.

Since the fee required for a transaction may change between the time when the original fee was calculated and the time when the transaction is submitted, it is wise to use the fee_cushion to ensure that the transaction will go through. For example, suppose the original fee calculated for a transaction was 10 stroop but at the instant the transaction is submitted the server is experiencing a higher load and it has raised its minimum fee to 12 stroop. Without a fee_cushion, this transaction would not be processed by the server, but with a fee_cushion of, say, 1.5 it would be processed and you would just pay the 2 extra stroop.

The max_fee option can be used to avoid submitting a transaction to a server that is charging unreasonably high fees.

##4. Submitting a trade offer to the network

Submitting a trade offer to the network is similar to submitting a payment transaction. Here is an example for a trade that expires in 24 hours where you are offering to sell 1 USD in exchange for 100 STR:

/* Loading stellar-lib Remote and Amount modules in Node.js */ 
var Remote = require('stellar-lib').Remote;
var Amount = require('stellar-lib').Amount;

/* Loading stellar-lib Remote and Amount modules in a webpage */
// var Remote = stellar.Remote;
// var Amount = stellar.Amount;

var MY_ADDRESS = 'rrrMyAddress';
var MY_SECRET  = 'secret';

var BUY_AMOUNT = Amount.from_human('100STR');
var SELL_AMOUNT = Amount.from_human('1USD');

// EXPIRATION must be a Date object, leave undefined to submit offer that won't expire
var now = new Date();
var tomorrow = new Date(now.getTime() + (24 * 60 * 60 * 1000));
var EXPIRATION = tomorrow;

var remote = new Remote({ /* Remote options */ });

remote.connect(function() {
  remote.set_secret(MY_ADDRESS, MY_SECRET);

  var transaction = remote.transaction();

  transaction.offer_create({
    from: MY_ADDRESS, 
    buy: BUY_AMOUNT, 
    sell: SELL_AMOUNT, 
    expiration: EXPIRATION
  });

  transaction.submit(function(err, res) {
    /* handle submission errors / success */
  });
});

##5. Listening to the network

In some (relatively rare) cases you may want to subscribe to the network event feed and listen for transactions and the ledger closings.

 /* Loading stellar-lib with Node.js */
  var Remote = require('stellar-lib').Remote;

  /* Loading stellar-lib in a webpage */
  // var Remote = stellar.Remote;

  var remote = new Remote({options});

  remote.connect(function() {
    remote.on('transaction_all', transactionListener);
    remote.on('ledger_closed', ledgerListener);
  });

  function transactionListener (transaction_data) {
    // handle transaction_data
    // see https://www.stellar.org/api/#api-subscribe for the format of transaction_data
  }

  function ledgerListener (ledger_data) {
    // handle ledger_data
    // see https://www.stellar.org/api/#api-subscribe for the format of ledger_data
  }

• https://https://www.stellar.org/api/#api-subscribe