Kin Ecosystem Payment Service

The payment-service is a service meant to be run internally, i.e. not directly connected to the internet. It provides the functionality to:

• send KIN payments
• subscribe on KIN payments sent/received on any given address
• fund new stellar wallets

The service is initiated with a root wallet account that contains sufficient KIN and XLM. The service is diveded into 3:

1. Http server for incoming requests
2. Background worker to process payment requests and perform callbacks
3. Polling process that listens on the blockchain and sends callbacks on any transaction involving a presubscribed address

The server implements a global lock over payment ids, to prevent double spend in case of race-conditions. The server - worker communication is implemented over redis, using the rq library.

Setup

The service expects configuration given via configuration variables:

• APP_REDIS redis url ('redis://localhost:6379/0')
• APP_PORT web app port (5000)
• STELLAR_HORIZON_URL horizon url ('https://horizon-kik.kininfrastructure.com')
• STELLAR_NETWORK stellar network name or passpharse ('PUBLIC'/'TESTNET'/'private testnet')
• STELLAR_KIN_ISSUER_ADDRESS stellar asset issuer ('GBQ3DQOA7NF52FVV7ES3CR3ZMHUEY4LTHDAQKDTO6S546JCLFPEQGCPK')
• STELLAR_KIN_TOKEN_NAME stellar asset name ('KIN')
• KIN_FAUCET url of a KIN faucet ('http://159.65.84.173:5000') - used for generate-funding-address makefile target
• XLM_FAUCET url of a XLM faucet/ friendbot ('http://friendbot-kik.kininfrastructure.com')
• STELLAR_INITIAL_XLM_AMOUNT initial amount of XLM when funding a wallet (2)

An example for these variables exists in local.sh. The makefile uses this file to export the variables and run the services.

In addition to the public configuration, there is a "secret" configuration which contains the stellar private keys for the root wallet of the service (this is the wallet that will create accounts and send KIN):

• STELLAR_BASE_SEED Main stellar secret key

They can either be generated using the make generate-funding-address script or manually created. Make sure the address contains enough KIN and XLM for operation.

For the worker, you need to configure a CHANNEL_SALT that will be used to derive a channel to sign outgoing transactions and enable concurrency across multiple workers.

Flow

The payment-service is intended to run in an internal network detached from the internet. A user facing web app receives internet traffic and decides to pay a user.

Pay

POST /payments - see swagger for details

The endpoint receives the information for the payment including an id, amount, recipient wallet and completion_callback, and creates a background task to pay the given wallet:

class PaymentRequest(ModelWithStr):
    amount = IntType()
    app_id = StringType()
    recipient_address = StringType()
    id = StringType()
    callback = StringType()  # a webhook to call when a payment is complete

The blockchain transaction will include the app_id and id of the payment in the memo field.

Once the payment is done, the payment-server notifies the completion_callback using an HTTP POST method including the payment information:

class Payment(ModelWithStr):
    id = StringType()
    app_id = StringType()
    transaction_id = StringType()
    recipient_address = StringType()
    sender_address = StringType()
    amount = IntType()
    timestamp = DateTimeType(default=datetime.utcnow())

---

Say the user facing server decides to create a new wallet:

Create Wallet

POST /wallets

The payload is

class WalletRequest(ModelWithStr):
    wallet_address = StringType()
    app_id = StringType()

The app_id will be written to the blockchain transaction and wallet will be create (no notification/ callback).

---

When the user facing server, presents a spend offer, it can subscribe to updates on KIN payments to/from a specific address, by registering a callback

Watch

PUT/ POST /watchers/<service_id>

A few different services can register callbacks. Each service is identified by service_id.

class Watcher(ModelWithStr):
    wallet_addresses = ListType(StringType)
    callback = StringType()  # a webhook to call when a payment is complete
    service_id = StringType()

When the payment-service encounters a KIN payment including a registered wallet_address in either the to or from fields, it calls all the subscribed services' callback using the HTTP POST method with the payment payload (same as Pay command):

class Payment(ModelWithStr):
    id = StringType()
    app_id = StringType()
    transaction_id = StringType()
    recipient_address = StringType()
    sender_address = StringType()
    amount = IntType()
    timestamp = DateTimeType(default=datetime.utcnow())

---

In addition there are HTTP GET endpoints for getting information on a specific wallet balance or transactions, or getting information on a specific payment. The server has a healthcheck endpoint /status and a configuration endpoint /config that shows the blockchain configuration that the service is running with.

API

http://editor.swagger.io/?url=https://raw.githubusercontent.com/kinfoundation/ecosystem-api/master/payment.yaml

Development

Setting up a local development environment

This procedure is a work-in-progress and as of now is targeting MacOS machines, sorry others

Step 1: Clone this Repo

Step 2: Install dependencies

Change into the Repo's directory and run pipenv install (Python 3 and pipenv are prerequisites)

Step 3: Install and setup Redis

Install Redis

brew install redis

Create a link to launch Redis on startup:

ln -sfv /usr/local/opt/redis/*.plist ~/Library/LaunchAgents

Use launchctl to launch redis:

launchctl load ~/Library/LaunchAgents/homebrew.mxcl.redis.plist

Step 4: create or set the secrets file with wallet data

You need to have a stellar account with funds and create a secrets/.secrets file locally with the following content:

export STELLAR_BASE_SEED=SXXX

Step 5: Run the service (hopefully)

Run make which will run 3 processes:

• payment-service web
• worker
• watcher

Running in Docker

To run and test using docker follow the instructions bellow:

Setup

Download docker + docker-compose for your environment.

If you DON'T have a wallet with XLM and KIN: Run the following command to generate a secrets/.secrets file with a pre-funded wallet:

make generate-funding-address

Note that this command will overwrite any existing file secrets/.secrets.

If you have a wallet with XLM and KIN: You need to have a stellar account with funds and create a secrets/.secrets file locally with the following content:

export STELLAR_BASE_SEED=SXXX

Run docker servers and system tests

Run the following command:

make up  # start all services