frontend-engineer-hiring-test

Chat Backend WebSocket API 1.0.0 documentation

Real-time chat server with WebSocket support for bidirectional messaging and reactions.

User identification is automatic based on client IP address. All messages are broadcast to all connected clients.

Limits & Scalability

• Max connections: 1000 concurrent WebSocket connections
• Rate limiting: 60 messages per minute per client
• Message history: Last 1000 messages kept in memory (FIFO)
• Connection timeout: 60 seconds without activity (ping/pong heartbeat)
• Message size: 500 characters max per message

Table of Contents

• Servers
  • development
• Operations
  • SEND /ws
  • SEND /ws
  • RECEIVE /ws
  • RECEIVE /ws
  • RECEIVE /ws

Servers

development Server

• URL: ws://localhost:8080/
• Protocol: ws

Development server

Operations

SEND /ws Operation

Send a new chat message

• Operation ID: sendMessage

Client sends a message that will be broadcast to all connected clients

Message Send Message send_message

• Message ID: sendMessage
• Content type: application/json

Payload

Name	Type	Description	Value	Constraints	Notes
(root)	object	-	-	-	additional properties are allowed
type	string	-	const ("send_message")	-	required
data	object	-	-	-	required, additional properties are allowed
data.text	string	Message content	-	<= 500 characters	required
data.author_name	string	Display name for the author	default ("Anonymous")	-	-

Examples of payload (generated)

{
  "type": "send_message",
  "data": {
    "text": "string",
    "author_name": "Anonymous"
  }
}

SEND /ws Operation

Toggle reaction on a message

• Operation ID: addReaction

Add or remove a reaction. If user already reacted with this emoji, it will be removed

Message Add Reaction add_reaction

• Message ID: addReaction
• Content type: application/json

Payload

Name	Type	Description	Value	Constraints	Notes
(root)	object	-	-	-	additional properties are allowed
type	string	-	const ("add_reaction")	-	required
data	object	-	-	-	required, additional properties are allowed
data.message_id	string	ID of the message to react to	-	format (uuid)	required
data.emoji	string	Emoji character	-	-	required

Examples of payload (generated)

{
  "type": "add_reaction",
  "data": {
    "message_id": "d7d9d9fd-478f-40e6-b651-49b7f19878a2",
    "emoji": "string"
  }
}

RECEIVE /ws Operation

Receive new messages

• Operation ID: receiveMessage

Server broadcasts new messages to all connected clients. On connection, all existing messages are sent

Message Message message

• Message ID: message
• Content type: application/json

Payload

Name	Type	Description	Value	Constraints	Notes
(root)	object	-	-	-	additional properties are allowed
type	string	-	const ("message")	-	required
data	object	-	-	-	required, additional properties are allowed
data.id	string	Unique message identifier	-	format (uuid)	required
data.text	string	Message content	-	-	required
data.author_id	string	User ID based on client IP	-	-	required
data.author_name	string	Display name	-	-	required
data.created_at	integer	Unix timestamp in seconds	-	format (int64)	required
data.reactions	object	Map of emoji to array of user IDs who reacted	-	-	required
data.reactions (additional properties)	array<string>	-	-	-	-
data.reactions (single item)	string	-	-	-	-

Examples of payload (generated)

{
  "type": "message",
  "data": {
    "id": "497f6eca-6276-4993-bfeb-53cbbbba6f08",
    "text": "string",
    "author_id": "string",
    "author_name": "string",
    "created_at": 0,
    "reactions": {
      "property1": [
        "string"
      ],
      "property2": [
        "string"
      ]
    }
  }
}

RECEIVE /ws Operation

Receive reaction updates

• Operation ID: receiveReactionUpdate

Server broadcasts reaction changes with the full updated message

Message Reaction Updated reaction_updated

• Message ID: reactionUpdated
• Content type: application/json

Payload

Name	Type	Description	Value	Constraints	Notes
(root)	object	-	-	-	additional properties are allowed
type	string	-	const ("reaction_updated")	-	required
data	object	-	-	-	required, additional properties are allowed
data.message_id	string	-	-	format (uuid)	required
data.emoji	string	-	-	-	required
data.user_id	string	-	-	-	required
data.action	string	-	allowed ("added", "removed")	-	required
data.message	object	-	-	-	required, additional properties are allowed
data.message.id	string	Unique message identifier	-	format (uuid)	required
data.message.text	string	Message content	-	-	required
data.message.author_id	string	User ID based on client IP	-	-	required
data.message.author_name	string	Display name	-	-	required
data.message.created_at	integer	Unix timestamp in seconds	-	format (int64)	required
data.message.reactions	object	Map of emoji to array of user IDs who reacted	-	-	required
data.message.reactions (additional properties)	array<string>	-	-	-	-
data.message.reactions (single item)	string	-	-	-	-

Examples of payload (generated)

{
  "type": "reaction_updated",
  "data": {
    "message_id": "d7d9d9fd-478f-40e6-b651-49b7f19878a2",
    "emoji": "string",
    "user_id": "string",
    "action": "added",
    "message": {
      "id": "497f6eca-6276-4993-bfeb-53cbbbba6f08",
      "text": "string",
      "author_id": "string",
      "author_name": "string",
      "created_at": 0,
      "reactions": {
        "property1": [
          "string"
        ],
        "property2": [
          "string"
        ]
      }
    }
  }
}

RECEIVE /ws Operation

Receive error messages

• Operation ID: receiveError

Server sends error messages when rate limits are exceeded or validation fails

Message Error error

• Message ID: error
• Content type: application/json

Payload

Name	Type	Description	Value	Constraints	Notes
(root)	object	-	-	-	additional properties are allowed
type	string	-	const ("error")	-	required
data	object	-	-	-	required, additional properties are allowed
data.error	string	Error message	examples ("Rate limit exceeded. Maximum 60 messages per minute.", "Invalid message format", "message text cannot be empty", "message too long (max 500 characters)")	-	required

Examples of payload (generated)

{
  "type": "error",
  "data": {
    "error": "Rate limit exceeded. Maximum 60 messages per minute."
  }
}