9 unstable releases (3 breaking)

0.8.1 Feb 3, 2021
0.2.5 Sep 1, 2020
0.2.3 Aug 18, 2020
0.2.0 Jul 15, 2020
0.0.10 Mar 30, 2020

#12 in #tari

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41K SLoC

Tari comms DHT module

The Tari network messaging library. See CommsBuilder for more information on using this library.


Tari Comms DHT


The tari_comms_dht crate adds DHT functionality to tari_comms. It provides two sets of middleware (inbound and outbound) which process incoming requests and outgoing messages respectively.

Attaching to comms

In tari_comms, incoming and outgoing messages are connected using two mpsc sender/receiver pairs. One for incoming messages (receiving InboundMessages) and one for outbound messages (sending OutboundMessages).

The DHT module consists of two middleware layers (as in tower_layer::Layer) which form an inbound and outbound pipeline for augmenting messages.

Inbound Message Flow

InboundMessages are received from the incoming comms channel (as in the receiver side of of the mpsc channel which goes into CommsBuilder::new().incoming_message_sink(sender)). Typically, a ServicePipeline from the tari_comms::middleware crate is used to connect a stream from comms to the middleware service.

InboundMessage(comms) -> DHT Inbound Middleware -> DhtInboundMessage(domain)

The DHT inbound middleware consist of:

  • DeserializeMiddleware deserializes the body of an InboundMessage into a DhtEnvelope.
  • DecryptionMiddleware attempts to decrypt the body of a DhtEnvelope if required. The result of that decryption (success or failure) is passed to the next service.
  • ForwardMiddleware uses the result of the decryption to determine if the message is destined for this node or not. If not, the message will be forwarded to the applicable peers using the OutboundRequester (i.e. the outbound DHT middleware).
  • DhtHandlerMiddleware handles DHT messages, such as Join and Discover. If the messages are not DHT messages the next_service is called.

Outbound Message Flow

OutboundMessages are sent to the outgoing comms channel (as in the receiver side of of the mpsc channel which goes into CommsBuilder::new().outgoing_message_stream(receiver)). Typically, a ServicePipeline from the tari_comms::middleware crate is used to connect a stream from the domain-level to the middleware service and a SinkMiddleware to connect the middleware to the OMS in comms. Outbound requests to the DHT middleware are furnished by the OutboundMessageRequester, obtained from the Dht::outbound_requester factory method.

DhtOutboundRequest (domain) -> DHT Outbound Middleware -> OutboundMessage (comms)

The DHT outbound middleware consist of:

  • BroadcastMiddleware produces multiple outbound messages according on the BroadcastStrategy from the received DhtOutboundRequest message. The next_service is called for each resulting message.
  • EncryptionMiddleware encrypts the body of a message if DhtMessagheFlags::ENCRYPTED is given. The result is passed onto the next_service.
  • SerializeMiddleware wraps the body in a DhtEnvelope, serializes the result, constructs an OutboundMessage and calls next_service. Typically, next_service will be a SinkMiddleware which send the message to the comms OMS.


#use tari_comms::middleware::ServicePipeline;
#use tari_comms_dht::DhtBuilder;
#use tari_comms::middleware::sink::SinkMiddleware;
#use tari_comms::peer_manager::NodeIdentity;
#use rand::rngs::OsRng;
#use std::sync::Arc;
#use tari_comms::CommsBuilder;
#use tokio::runtime::Runtime;
#use futures::channel::mpsc;

let runtime = Runtime::new().unwrap();
// Channel from comms to inbound dht
let (comms_in_tx, comms_in_rx)= mpsc::channel(100);
let (comms_out_tx, comms_out_rx)= mpsc::channel(100);
let node_identity = NodeIdentity::random(&mut OsRng::new().unwrap(), "".parse().unwrap())
let comms  = CommsBuilder::new(runtime.executor())
        // Messages coming from comms
        // Messages going to comms
let peer_manager = comms.start().unwrap().peer_manager();
let dht = DhtBuilder::new(node_identity, peer_manager).finish();

let inbound_pipeline = ServicePipeline::new(
    // In Tari's case, the service would be a InboundMessageConnector in `tari_p2p`
    dht.inbound_middleware_layer(/* some service which uses DhtInboundMessage */ )
// Use the given executor to spawn calls to the middleware

let outbound_pipeline = ServicePipeline::new(
    // SinkMiddleware sends the resulting OutboundMessages to the comms OMS
// Use the given executor to spawn calls to the middleware

let oms = dht.outbound_requester();


~761K SLoC