Go Interview - Gossamer

Task Description

Implement a peer-to-peer (p2p) message tracker. There is a Message type that is found in network/message.go.

// Message is received from peers in a p2p network.
type Message struct {
	ID     string
	PeerID string
	Data   []byte
}

Each message is uniquely identified by the Message.ID. Messages with the same ID may be received by multiple peers. Peers are uniquely identified by their own ID stored in Message.PeerID.

The interface for the message tracker is defined in network/message_tracker.go.

// MessageTracker tracks a configurable fixed amount of messages.
// Messages are stored first-in-first-out.  Duplicate messages should not be stored in the queue.
type MessageTracker interface {
	// Add will add a message to the tracker
	Add(message *Message) (err error)
	// Delete will delete message from tracker
	Delete(id string) (err error)
	// Get returns a message for a given ID.  Message is retained in tracker
	Message(id string) (message *Message, err error)
	// All returns messages in the order in which they were received
	Messages() (messages []*Message)
}

There is an exported constructor network.NewMessageTracker(length int) which accepts a length parameter. This parameter should be used to constrain the number of messages in your implementation.

There are some tests within the network_test package found in network/message_tracker_test.go which call the network.NewMessageTracker and test the functionality from outside the network package.

There are a few key points to take into account when implementing this tracker:

• The tracker is meant to be a hot path in our program so performance is critical.
• Duplicate messages based on Message.ID should only be returned by MessageTracker.All() once.
• The tracker should only hold a configurable maximum amount of messages so it does not grow in size indefinitely.

Submission Criteria

• Implement the MessageTracker interface, and ensure tests in network/message_tracker_test.go pass.
• Write unit tests for your MessageTracker implementation and obtain 70%+ code coverage.
• BONUS: Write benchmarks for your tracker implementation.
• BONUS: Write a design document that describes your implementation and the technical choices that you made.

Submission

You must use git to track your changes.

You can either submit us:

• a URL to your Git repository
• a zip file containing your Git repository