Bridge Daemon

An overview of the Bridge Daemon

High-level Overview

The Bridge Daemon is implemented in the same way as other daemons in the dYdX Chain open source software. Specifically, the daemon:

• will be run in process as go routines, and

• will use gRPC for communication with the main application.

One-time Setup

1. Application initializes gRPC server

2. The daemon initializes gRPC client

   1. need to make a connection to localhost:9090 for query service

   2. need to make a connection to unix socket for private daemon service

Related Module

x/bridge module

Daemon

Main Loop Logic

Query Protocol for the Next Event ID

Let n be the nextRecognizedEventId on the in-memory BridgeEvents struct on thex/bridge module.

Let c be the ProposeParams.MaxBridgesPerBlock parameter on the x/bridge module.

Search for next bridge log

For each Ethereum node endpoint configured, use the eth_getLogs RPC call with the following parameters:

• address : BridgeContractAddress

• topics : [ sha256(LogBridge(…)) , [ n , n+1 , … , n+c-1 ]]

• from_block : "ethereum block height of last recognized bridge event"

• to_block : "finalized"

Update the Server

For each event returned by each of the Ethereum nodes, send a single, batched AddBridgeEventsRequest to the server with the events in-order.

Sleep

To prevent hogging resources (from the validator itself or the remote Ethereum Node), the go routine can sleep until the next iteration. It can use the ProposeParams.ProposeDelayDuration parameter on the x/bridge module to determine a suitable sleep time. Ideally it would sleep for no more than about half of this interval.

Configuration

These should be configurable by a validator.

EthereumNodeRpcEndpoint : The daemon maintains an Ethereum node RPC endpoint.

Ideally, this should be a list of RPC endpoints and every RPC query will be sent to each node and daemon will only proceed if each node provides the same response. However, if a validator hosts its own Ethereum node, then it can use a single endpoint. All 16 private-testnet validators who responded to a dYdX survey indicated that they will host their own Ethereum full nodes.

BridgeContractAddress : The bridge contract to query logs from.

RPC Interface

// BridgeService defines the gRPC service used by bridge daemon.
service BridgeService {
    // Sends a list of newly recognized bridge events.
    rpc AddBridgeEvents(AddBridgeEventsRequest)
        returns (AddBridgeEventsResponse);
}

// AddBridgeEventsRequest is a request message that contains a list of new bridge
// events. The events should be contiguous and sorted by (unique) id.
message AddBridgeEventsRequest {
    repeated dydxprotocol.bridge.BridgeEvent bridge_events = 1
        [ (gogoproto.nullable) = false ];
}

// AddBridgeEventsResponse is a response message for BridgeEventRequest.
message AddBridgeEventsResponse {}

Information is stored in the BridgeEvent struct as described in x/bridge.