This is a repository for TrustWallet's take home assignment

Assignment

The details of the assignment here

For the sake of simplicity, here are assumptions based on the requirements of the assignment:

• The project runs in a single thread, parsing blocks one by one. No re-org handling.
• GetTransactions return transactions of the latest parsed block, no pagination.
  • Only store the latest block's transaction data for each address. No historical data is saved.
  • If the latest parsed block does not have transactions for the subscribed address -> return empty list.
• On Ethereum Blockchain the block time is 12s (approximately), meaning when crawl latest block on the chain, we can let the job run interval every 4s.
• Avoid usage of external libraries: gin-gonic/gin, go-ethereum, etc.
  • Use Go's net/http package to make requests to the Ethereum JSONRPC API.
  • Use Go's built-in data structures to store in memory data.
  • Use simple REST API for expose public interface.
  • Let testify is the exception because it is used to support write tests and mock.

Main components

Crawler

Interval (every 4 seconds) running job to get latest block from ethereum and extract transactions filtered by subscribed addresses.

Using the Repository to get addresses and save block data.

Call RPC node to get block data:

• eth_blockNumber
• eth_getBlockByNumber

Parser

Handle and expose public interface for biz logic:

type Parser interface {
	// last parsed block
	GetCurrentBlock() int

	// add address to observer
	Subscribe(address string) bool

	// list of inbound or outbound transactions for an address
	GetTransactions(address string) []Transaction
}

Repository

Handle storage queries:

type Repository interface {
	// last parsed block 
	GetCurrentBlock() (int, error)

	// get list of subscribed addresses 
	GetAddresses() ([]string, error)

	// list of transactions for an address 
	GetTransactions(address string) ([]Transaction, error)
	
	// add a address to list of subscription
	AddAddress(address string) error
	
	// save the list of transactions
	SaveTransactions(blockNum int, txn []Transaction) error
}

How to run

When run main, the code will start both the crawler job and the APIs server

go run cmd/tx-parser/main.go

Example of the 3 APIs:

• GET /current-block

curl --location 'http://localhost:8080/current-block'

• POST /subscribe

curl --location 'http://localhost:8080/subscribe' \
--header 'Content-Type: application/json' \
--data '{
    "address": "0xf15689636571dba322b48e9ec9ba6cfb3df818e1"
}'

• GET /transactions

curl --location 'http://localhost:8080/transactions?address=0x95222290dd7278aa3ddd389cc1e1d165cc4bafe5'