Concurrent Money Transfer System

Overview

This is a concurrent money transfer system built in Go to handle money tarnsfers between users with built in protections.

Features

• Creation of Users/accounts with starting balance.
• Make Transfer to other users
• Atomic Money Tranfers
• Prevention of overdrafts
• Concurrently safe account operations

Pre-requisites

Go 1.20 or higher

Setup and Installation

1. Clone the repository
2. Run go mod tidy to download all dependencies
3. Run the application with go run cmd/main.go

API Endpoints

1. Create Account

URL: /account/create Method: POST Request Body

{
  "user_id": "kowshik",
  "balance": 25.50
}

Response Body

{"status":"account created","user_id":"kora"}

2. Get Balance

URL: /account/balance?user_id=kowshik Method: GET

Response Body

{"balance":25.50}

3. Transfer

URL: /transfer Method: POST

Request Body

{
    "from_user_id" : "kowshik",
    "to_user_id" : "ram",
    "amount": 15.45
}

Response Body

{"status":"transfer successful"}

Locking Strategy and Implementations

1. Grained Lock on Individual Accounts during Transfer

   • Instead of using a global lock on all transfers , we lock the two accounts involved in a transfer.
   • This improves concurrency cuz we can allow multiple transfers happening at the same time.

2. Implemented Ordered Locking to prevent deadlock

   • When two users send money to each other at same time, it may lock in different orders causing deadlock. So to avoid that we compare user_ids and do a ordered lock.

3. RWMutex during Concurrent Reads

   • Get account balance would be used in different places including exposing in a API and also during transfer to fetch the current balance. So implemented read-only lock so that multiple goroutines can read them concurrently.

Sample Curls for testing

Account Create

curl --location 'http://localhost:8080/account/create' \
--header 'Content-Type: application/json' \
--data '{
    "user_id" : "kora",
    "balance": 50
}'

Get account Balance

curl --location 'http://localhost:8080/account/balance?user_id=kora' \
--data ''

Transfer money

curl --location 'http://localhost:8080/transfer' \
--header 'Content-Type: application/json' \
--data '{
    "from_user_id" : "kora",
    "to_user_id" : "kowshik",
    "amount": 50
}'