Elixir technical test

This technical test is for backend developers who already know elixir & OTP. The test will take 1h15.

General acceptance criteria

• You cannot use external dependencies.
• Code accuracy matters. A readable, safe, refactorable code is a plus.

The project

You will create a very simple in memory key-value store (a simpler Redis clone) in elixir.

Usage example:

iex> Redis.execute(["PING"])
"PONG"

iex> Redis.execute(["SET", "hello", 42])
:ok

iex> Redis.execute(["GET", "hello"])
42

Each command is an elixir list where the head is the command name and the rest of the list are the arguments.

Commands to implement

PING

PING [message]

Returns PONG if no argument is provided, otherwise return a copy of the argument.

SET

SET key value

Set key to hold the string value. If key already holds a value, it is overwritten, regardless of its type.

GET

GET key

Get the value of key. If the key does not exist the special value nil is returned.

EXPIRE

EXPIRE key seconds

Set a timeout on key. After the timeout has expired, the key will automatically be deleted. A key with an associated timeout is often said to be volatile in Redis terminology.

PERSIST

PERSIST key

Remove the existing timeout on key, turning the key from volatile (a key with an expire set) to persistent (a key that will never expire as no timeout is associated).

How to store the state?

There are multiple way to store state in elixir. Choose the one you like best and explain to me what the tradeoffs are (verbally during the code review).

Bonus (not required)

Accept TCP connections on port 6379.

We should be able to use the 5 commands listed above using the redis CLI as a client.

Example:

$ brew install redis

$ redis-cli PING
"PONG"

You will need to deserialize / serialize data using the Redis Protocol specification.