wallet-api

wallet-api

Service stores account balances and provide one with functionality of transferring money from one account to another.

Domain

For detailed API documentation see /docs/API.md. You can find DDD like description at code-level in services/transfers/domain.go.

Business assumptions

• All IDs here are uuid4.
• Service support multiple currencies each one with precision specified in DB.
• Term transfer suits better than payment.
• No functionality for deposit/withdraw - just inner transfer.
• Each transfer consist of one(deposit/withdraw) or two(inner) parts that are denormalized (for better read performance).
• Transfer amount rounding without any error if there is extra precision specified.

Business conventions

• 'USD' and 'usd' means the same, but we use first for inner representation.
• Transfer operations positive-idempotent(means after succeeded once it will always return 'OK' without duplication).

Tech assumptions

• Service simplified - there is no prometheus metrics, tracing and extra logging.
• It's supposed to run in k8s - there is no service discovery logic.
• For supported configuration flags see ./cmd/api/config.go.
• When started server tries connect to DB until succeed or retries count exceeded(see configuration options).
• To stop server gracefully you need to send SIGHUP, and it will try do it in time specified via configuration.

DB layout

Configuration

Usage of /bin/api:
  -db string
    	db connections credentials
  -dbRetryCount uint
    	retry count for connecting to db (default 10)
  -dbRetryTimeout duration
    	retry timeout for connecting to db (default 2s)
  -logLevel string
    	debug|info|warn|error (default "info")
  -port string
    	port (default "8080")
  -shutdownTimeout duration
    	graceful shutdown timeout (default 10s)

Questions and features to be considered for future

• Separation for booking and spending for 2-phase transactions.
• Pagination for 'all' methods.
• Currencies exchange.
• Deposit/Withdraw from outside world.
• Additional API methods.

How to run code or develop

Preparations

You need install:

• docker and docker-compose
• https://taskfile.dev

Run locally

task build_dev_tools # builds tooling image
task up # run all in docker compose
# wait some time until PostgreSQL will statred
task migrate # apply migrations inside docker-compose started by task up
task -l # for available tasks for development

Development

Some task commands may require tools that presented in docker image that can build from tools/Dockerfile-tools via task build_dev_tools.

Attaches git hooks for running test/linter in development process lifecycle, also prepending each commit msg with [<branch_name>] prefix for later investigations via git blame.

task attach_hooks

After you start and change something modd rebuild and restart app via ./tools/modd.conf There is also ./integration/init.sql file that maybe useful if you decide to populate DB with test data.

Tests

task test # if have go installed or inside go-dev-tools docker image
task run_integration_tests # runs integration tests via docker-compose 

Build Docker image for deployment

Be aware you need to run migrations before image deploy (e.g. via k8s job)

IMAGE_NAME=wallet-api:1.0.0 task build_api_image

Things used

Code

• go1.15.2.
• docker and docker-compose.
• PostgreSQL.
• https://github.com/shopspring/decimal - decimal numbers processing.
• https://github.com/gorilla/mux - http routing.
• https://github.com/oklog/run - for managing top-level gorutines.

Tools

• https://github.com/DATA-DOG/go-sqlmock - SQL mocks for unit tests.
• https://github.com/stretchr/testify/assert - test assertions.
• https://github.com/rubenv/sql-migrate - DB migrations.
• https://github.com/golangci/golangci-lint - go linter.
• https://github.com/cortesi/modd - watcher for restarting code after changes.
• https://github.com/go-task/task - task runner better make alternative.
• https://github.com/go-kit/kit - microservices instrumentation.
• githooks - local code quality management.
• travis ci - CI.