Servers provide prices to Clients and Clients provide signed orders to Servers.

Protocol

In Last Look, Clients are signers and Servers are senders.

1. Client establishes a bidirectional (e.g. WebSocket) connection to the Server.

2. Client calls subscribeLevels on the Server with a list of token pairs.

3. Server periodically calls updateLevels on the Client for each token pair.

4. Client calls provideOrder on the Server with a signed order.

5. Server may send the signed order to Ethereum for settlement.

Levels

Each level is a tuple of amount and price at that level. In the following example, a senderAmount up to 100 has price 0.3, from 100 to 1000 has price 0.2, and so on.

  [100, 0.1],
  [1000, 0.2],
  [10000, 0.3]

The Server has indicated that it would accept orders with the following values:

1. senderAmount of 100 and signerAmount of 10.

2. senderAmount of 500 and signerAmount of 90 because the first 100 is 10 and the next 400 is 80.

3. senderAmount of 5000 and signerAmount of 1390 because the first 100 is 10, the next 900 is 180, and the next 4000 is 1200.

There is no minimum and the maximum is the largest senderAmount.

Server Methods

In Last Look protocols, the Client is the order signer and Server the order sender.

subscribeLevels

A request to receive updates to for a token pair. Returns the current price levels.

subscribeLevels(
  signerToken: string, // Token the Client would transfer
  senderToken: string  // Token the Server would transfer
): Levels

unsubscribeLevels

A request to stop receiving updates for a token pair. Returns a boolean.

unsubscribeLevels(
  signerToken: string, // Token the Client would transfer
  senderToken: string  // Token the Server would transfer
): boolean

getLevels

Given a token pair, return an array of price levels.

getLevels(
  signerToken: string, // Token the Client would transfer
  senderToken: string  // Token the Server would transfer
): Levels

provideOrder

Provide a signed order to be filled or ignored. Response should be a transaction ID.

provideOrder(
  order: Order // Signed order as specified below
): string

Client Methods

updateLevels

Update price levels for a token pair. This is a notification so returns no result.

updateLevels(
  levels: Levels // Levels object as specified below
)

Example

Calls are JSON-RPC over WebSocket. Take getLevels as an example.

Client connects and sends the following message to the Server:

{
  "jsonrpc": "2.0",
  "id": 123,
  "method": "getLevels",
  "params": {
    "signerToken": "0xdac17f958d2ee523a2206206994597c13d831ec7",
    "senderToken": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2"
  }
}

Server then sends the following message to the Client:

{
  "jsonrpc": "2.0",
  "id": 123,
  "result": {
    "signerToken": "0xdac17f958d2ee523a2206206994597c13d831ec7",
    "senderToken": "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
    "levels": [
      [100, 0.002132234],
      [1000, 0.002002234],
      [10000, 0.001992234]
    ]
  }
}

Types

Levels

Tuple with an amount of signerToken and respective amount of senderToken in atomic units.

{
  signerToken: string              // Token the Client would transfer
  senderToken: string              // Token the Server would transfer
  levels: Array<[string, string]>  // Array of price levels
}

Order

Object with the parameters of a signed order to be filled.

{
  nonce: string,        // Single use nonce
  expiry: string,       // Expiry in seconds
  signerWallet: string, // Wallet of the Client
  signerToken: string,  // Token the Client would transfer
  signerAmount: string, // Amount the Client would transfer
  senderToken: string,  // Token the Server would transfer
  senderAmount: string, // Amount the Server would transfer
  v: string,            // ECDSA signature
  r: string,
  s: string
}