Disco

Disco is a discovery server for Babble groups. It offers an API to advertise and manage Babble groups, as well as a WebRTC signaling mechanism and TURN server, which can be used by Babble in webrtc mode to establish p2p connections in the face of NATs.

Table of Contents

• Usage
• Discovery
  • Add a group
  • List groups
  • Get a specific group
  • Update a group
  • Delete a group
  • TTL
• WebRTC Signaling
• TURN
• Caveats

Usage

Discovery service for Babble

Usage:
  disco [flags]

Flags:
      --address string          Advertise address (use public address) (default "0.0.0.0")
      --cert-file string        File containing TLS certificate (default "cert.pem")
      --disco-port string       Discovery API port (default "1443")
  -h, --help                    help for disco
      --ice-password string     ICE server password corresponding to username (default "test")
      --ice-port string         ICE server port (default "3478")
      --ice-username string     ICE server userame. Only this user will be allowed to use the ICE server (default "test")
      --key-file string         File containing certificate key (default "key.pem")
      --realm string            Administrative routing domain within the WebRTC signaling (default "main")
      --signal-port string      WebRTC-Signaling port (default "2443")
      --ttl duration            Group Time To Live, after which groups will be deleted (default 5m0s)
      --ttl-hearbeat duration   Ticker frequency for checking group TTL (default 1m0s)

The discovery API, WebRTC-signaling router, and TURN server are exposed on different ports, disco-port (default 1443), signal-port (default 2443), and ice-port respectively.

The discovery API and WebRTC-signaling router bind to all interfaces 0.0.0.0 and are secured with TLS, with the same underlying certificate. The certificate and key files are specified with cert-file and key-file options.

The TURN server also binds to 0.0.0.0 but it advertises itself at the address specified by --address. This must be the public IP of the machine running the server, as it will be used as a TURN relay address.

The ice-username and ice-password options define the credentials of a single user allowed to authenticate and use the TURN server. Babble has homonymous config options to match the username and password fields when using the Disco TURN server.

To get started with a localhost disco server, simply run:

make run

Discovery

The discovery API offers a mechanism to create, discover, and manage Babble groups. A Babble group defines a set of peers engaged in a Babble consensus network.

The following sections describe the API calls using curl, but first we need curl to trust the self-signed certificate in test_data/cert.pem:

export CURL_CA_BUNDLE=test_data/cert.pem

Add a group

POST https://localhost:1443/group

 curl --location --request POST 'https://localhost:1443/group' \
--header 'Content-Type: application/json' \
--data-binary @new_group.json

where new_group.json contains the json for a new group:

{
	"Name": "office group",
	"AppID": "BabbleChat",
	"Peers": [ 
		{
			"NetAddr":"thenetaddr",
			"PubKeyHex":"thepubkey",
			"Moniker":"Monica"
		}
	],
	"GenesisPeers": [
		{
			"NetAddr":"thenetaddr",
			"PubKeyHex":"thepubkey",
			"Moniker":"Monica"
		}
	]
}

Note that the ID field of the group is omitted. This is because it will be randomly generated by the server. If the ID is specified, the server will either update the group in place, or create a new one with that ID.

List groups

GET https://localhost:1443/groups?app-id=

Use the app-id query parameter to return only the groups belonging to a certain application.

{
	"8f41c928-360b-4202-90f1-a7efa6b7ffd3": {
		"ID":"8f41c928-360b-4202-90f1-a7efa6b7ffd3",
		"Name":"office group",
		"AppID":"BabbleChat",
		"PubKey":"",
		"LastUpdated":1583773505,
		"Peers":[
			{
				"NetAddr":"thenetaddr",
				"PubKeyHex":"thepubkey",
				"Moniker":"Monica"
			}
		],
		"InitialPeers":[
			{
				"NetAddr":"thenetaddr",
				"PubKeyHex":"thepubkey",
				"Moniker":"Monica"
			}
		]
	}
}

Get a specific group

GET https://localhost:1443/groups/{ID}

{
	"ID":"8f41c928-360b-4202-90f1-a7efa6b7ffd3",
	"Name":"office group",
	"AppID":"BabbleChat",
	"PubKey":"",
	"LastUpdated":1583773505,
	"Peers":[
		{
			"NetAddr":"thenetaddr",
			"PubKeyHex":"thepubkey",
			"Moniker":"Monica"
		}
	],
	"InitialPeers":[
		{
			"NetAddr":"thenetaddr",
			"PubKeyHex":"thepubkey",
			"Moniker":"Monica"
		}
	]
}

Update a group

PATCH https://localhost:1443/groups/2

 curl --location --request PATCH 'https://localhost:1443/group' \
--header 'Content-Type: application/json' \
--data-binary @updated_group.json

Delete a group

DELETE https://localhost:1443/groups/2

The group with ID 2 has been deleted successfully

TTL

It is possible to set a Time To Live (--ttl), and a ticker frequency (--ttl-hearbeat), to ensure that groups get deleted from the server after their TTL has expired.

WebRTC Signaling

The WebRTC Signaling Server enables Babble nodes to exchange connection information (SDP) prior to establishing a direct P2P link. It is implemented as a WAMP server (Web Application Messaging Protocol) which is basically RPC over secure websockets.

When using Babble with webrtc enabled, you can point to the Disco server's signal-port. If the server's TLS certificate is self-signed, you can copy the cert.pem file in Babble's data-directory.

TURN

The TURN server offers STUN/TURN services which can be used by Babble to establish P2P connections. It helps devices punch holes through NATs when this is possible, or relays packets on their behalf.

When using Babble with webrtc enabled, you can point to the Disco server's ice-port with the appropriate ice-username and ice-password to authenticate to, and use the Disco server's TURN services.

Improvements

Ideally, we would like the same disco server to be used by multiple apps. Group discovery, signaling, and TURN services, should occur within separate administrative domains (realms) for each application. This scheme would require developers to register their applications with the disco server, which would spin-up new instances of the services for each application and somehow authenticate application clients as to prevent them from accessing groups from other applications.

This separation is not implemented yet. Applications are sharing the same signaling router (same realm), and TURN server, and are not authenticated with the disco server. Groups are indexed by AppID and it is possible to query only groups pertaining to an AppID. This allows developers to only display those groups that are relevant to their application, but it is definitely not a secure system.

The group database is not persisted, meaning that all groups are lost when the server is restarted.

Updating and deleting groups should be protected to require authorisation from enough group members. Ultimately we should implement a Babble light-client for every group.

TTL should be configurable at the group level, to enable group creators to set their own TTL.