lsfr.io

HTTP API #

In this stage, you’ll build an in-memory key-value store and expose it over a REST API.

Endpoints #

You’ll implement the following endpoints:

  1. PUT /kv/{key}

Add or update a key-value pair in the store.

PUT /kv/{key}
Parameters:
  - key (path, required): The key to store (cannot be empty)
Body: Value to store as plain text (cannot be empty)
Response:
  - 200 OK: Key-value pair added or updated successfully
  - 400 Bad Request: Return "key cannot be empty\n" or "value cannot be empty\n"
  1. GET /kv/{key}

Retrieve the value associated with the given key.

GET /kv/{key}
Parameters:
  - key (path, required): The key to retrieve
Response:
  - 200 OK: Return the stored value
  - 404 Not Found: Return "key not found\n"
  1. DELETE /kv/{key}

Remove a key-value pair from the store.

DELETE /kv/{key}
Parameters:
  - key (path, required): The key to delete
Response:
  - 200 OK: Key deleted successfully (or key didn't exist)
  1. DELETE /clear

Remove all key-value pairs from the store.

DELETE /clear
Response:
  - 200 OK: All keys cleared successfully
  1. Error Handling

Unsupported HTTP methods on any endpoint should return:

  • 405 Method Not Allowed: Return “method not allowed\n”

Your API should handle concurrent requests safely. Consider thread safety when implementing your in-memory store.

Storage #

A simple in-memory map/dictionary is sufficient for storage in this stage. You’ll add persistence in the next stage.

Keys #

Keys must be URL-safe strings without spaces or forward slashes. Examples of valid keys:

  • country:capital
  • user_123
  • special:key-with_symbols.123

Values #

Values are stored as UTF-8 encoded text and can contain:

  • Unicode characters like 😊
  • Spaces and special symbols
  • Long strings (up to reasonable memory limits)

Testing #

You can test your implementation using the lsfr command. Your program should accept a --port flag that lsfr will use to tell it what port to run on.

$ lsfr test http-api
Running http-api: HTTP API with GET/PUT/DELETE Operations

✓ PUT Basic Operations
✓ PUT Edge and Error Cases
✓ GET Basic Operations
✓ GET Edge and Error Cases
✓ DELETE Basic Operations
✓ DELETE Edge and Error Cases
✓ Concurrent Operations
✓ Check Allowed HTTP Methods

PASSED ✓

Run 'lsfr next' to advance to the next stage.

Debugging #

When tests fail, lsfr will show you exactly what went wrong:

$ lsfr test
Running http-api: HTTP API with GET/PUT/DELETE Operations

✓ PUT Basic Operations
✓ PUT Edge and Error Cases
✓ GET Basic Operations
✗ GET Edge and Error Cases

GET http://127.0.0.1:42409/kv/nonexistent:key
  Expected response: "key not found\n"
  Actual response: "\n"

  Your server should return 404 Not Found when a key doesn't exist.
  Check your key lookup logic and error handling.

FAILED ✗

Read the guide: lsfr.io/kv-store/http-api