Writing stage instructions

Stage instructions are the heart of a CodeCrafters challenge. Remember that most learners will be new to both the CodeCrafters platform and your challenge itself, so it’s important to write clear, concise and helpful stage instructions.

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Structure

We recommend following this structure when writing stage instructions:

1. Hook: A short sentence that describes what the user will do in this stage.
2. Explanation: A longer explanation of the concepts involved in this stage, and what the user needs to implement.
3. Tests: A clear description of how the user’s program will be tested, and what the expected output/behaviour is.
4. Notes (optional): Any additional notes or tips that might be helpful for the user.

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Example

Here’s an example from the Redis challenge:

In this stage, you’ll add support for the TYPE command.

The TYPE command

The TYPE command returns the type of value stored at a given key.

It returns one of the following types: string, list, set, zset, hash, and stream.

Here’s how it works:

$ redis-cli set some_key foo
"OK"
$ redis-cli type some_key
"string"

If a key doesn’t exist, the return value will be “none”.

$ redis-cli type missing_key
"none"

The return value is encoded as a simple string.

Tests

The tester will execute your program like this:

$ ./spawn_redis_server.sh

It’ll then send a SET command to your server.

$ redis-cli set some_key foo

It’ll then send a TYPE command to your server.

$ redis-cli type some_key

Your server should respond with +string\r\n, which is string encoded as a RESP simple string.

It’ll then send another TYPE command with a missing key.

$ redis-cli type missing_key

Your server should respond with +none\r\n, which is none encoded as a RESP simple string.

Notes

• For now, you only need to handle the “string” and “none” types. We’ll add support for the “stream” type in the next stage.