CRO Test

Crypto dot com backend test. I spent about 6 hrs finishing the project and reviewing the code. I provide a docker-compose to build a server easily and swagger document for testing.

Contents

• Getting started
  • Run Test
  • Run Server
• System Design
  • Project Layout
  • Class Diagram
  • DB Transaction Design
  • DB Index Design
  • API Usage
• ToDo And Dependencies

Getting started

go mod vendor

Run Test

step 1 : build test mysql instance

make run.test.mysql

step 2 : run test

go test -p=1 ./internal/test/...

note: if test occur driver: bad connection error, please run again.

Run Server

run with docker-compose docker-compose install

make compose.up

run local

go mod vendor
make run.local.mysql
make migrate.local.up
make run.server env=local

note: After running server with docker-compose, you can use swagger to test api.

System Design

Project Layout

This project layout is adopted a idea from golang standard project layout and clean architecture

• internal/domain : Domain layer define domain-logic interfaces. It can be used to comply Inversion dependency principle.
• internal/app : This package is used to manage dependency and initialize application.
• internal/model : Define data structure and its behavior.
• internal/service: Servicer layer implement core business logic.
• internal/delivery : Handler layer which act as the presenter. It could be RESTful, graphQL or gRPC. Delivery layer will be RESTful API in this project.
• internal/repository: Repository provide db operation and encapsulate database-specific logic (e.g SQL).
• internal/test : Test code and factory object. The test include concurrency testing.
• pkg/config : This package used to initialize configuration.
• build/migrations : db schema

Class Diagram

|users| -has-many-> |wallets| -has-many-> |transactions|

DB Transaction Design

Transferring money between wallets should consider race condition when multiple requests are processed simultaneously.

The most safe way is used to FOR UPDATE SQL to put a write lock on record. However, we can use optimistic lock to have better performance.

Therefore, I use following SQL to update wallet balance.

UPDATE wallets SET amount=amount-? WHERE amount >= ? AND serial_number = ?;

If this update statement show no rows affected, you can determine amount of this wallet is insufficient.

DB Index Design

Considering that users might need to review their transaction, we need to add proper index on transactions table.

The most common search scenario will be search transactions during a period, so I create two composite indexes idx_to_wallet_id_created_ati and idx_from_wallet_id_created_ati for this search scenario.

These indexes does not include kind column because kind column can be multiple values in search condition.

API Usage

swagger URI : http://localhost:8080/swagger/index.html

Authentication : After creating an account, you can use /api/v1/auth api to get your token, then put your token in Authentication header with Bearer schema. POST /api/v1/signup : create an account and wallet POST /api/v1/auth : get token

Wallet : POST /api/v1/wallets : create wallet GET /api/v1/wallets/:serial : get wallet and its transactions in 7dys. GET /api/v1/wallets : get all wallets.

Transaction : POST /api/v1/transfer : transfer money POST /api/v1/deposit : deposit money POST /api/v1/withdraw : withdraw money

ToDo And Dependencies

ToDo

• List wallets and transactions meanwhile solve n+1 query problem.
• Allow users to search their transactions.
• Provide delete api by implementing soft delete operation.
• Add cicd flow (e.g travis-ci, ansible).
• Add kubernetes deployment and Helm chart.
• Add redis rate limiter (e.g leaky bucket).
• Improve security with CORS, HTTPs and CSRF secret.
• Add performance monitoring mechanism (e.g Elastic APM and OpenTelemetry).
• Provide gRPC endpoints.

Dependencies

• echo for http server.
• fx for dependency injection.
• testify for building test suite.
• gogo-factory for building factory object.
• sqlxx for extension of sqlx.
• viper for configuration management.
• zap for logger.
• jwt-go for JWT token.
• goose for db migrations.