go-waku/docs/api/filter.md

Receive messages using Waku Filter

WakuFilter is a protocol that enables subscribing to messages that a peer receives. You can find Waku Filter's specifications on Vac RFC. This is a more lightweight version of WakuRelay specifically designed for bandwidth restricted devices. This is due to the fact that light nodes subscribe to full-nodes and only receive the messages they desire.

Create a waku instance

package main

import (
	"context"
    "fmt"

	"github.com/waku-org/go-waku/waku/v2/node"
	"github.com/waku-org/go-waku/waku/v2/protocol/filter"
)

...
wakuNode, err := node.New(node.WithWakuFilter(false))
if err != nil {
    fmt.Println(err)
    return
}

if err := wakuNode.Start(context.Background()); err != nil {
    fmt.Println(err)
    return
}
...

Options

One of these options must be specified when instantiating a node supporting the waku relay protocol

• WitWakuFilter(isFullNode, opts ...pubsub.Option) - enables the waku filter protocol and receives an optional list of options to configure the protocol

Adding a peer and receiving messages

...

peerAddr, err := multiaddr.NewMultiaddr("/dns4/node-01.do-ams3.waku.test.statusim.net/tcp/30303/p2p/16Uiu2HAkykgaECHswi3YKJ5dMLbq2kPVCo89fcyTd38UcQD6ej5W")
if err != nil {
    panic(err)
}

_, err = wakuNode.AddPeer(peerAddr, string(filter.FilterID_v20beta1))
if err != nil {
    panic(err)
}

// Setting the content filter
cf := filter.ContentFilter{
    Topic:         "/waku/2/default-waku/proto",
    ContentTopics: []string{contentTopic},
}

_, subscription, err := wakuNode.Filter().Subscribe(context.Background(), cf)
if err != nil {
    panic(err)
}

for env := range subscription.Chan {
    fmt.Println("Received msg:", string(value.Message().Payload))
}
...

To receive messages sent via the relay protocol, you need to subscribe to a pubsub topic. This can be done via any of these functions:

• wakuNode.Filter().Subscribe(ctx, contentFilter, opts) - subscribes to receive messages that match a specific contentFilter

This function return a Filter subscrition. To stop receiving messages in this channel wakuNode.UnsubscribeByFilter(ctx, theFilter) can be executed which will close the subscription and channel for the filter. wakuNode.Unsubscribe and wakuNode.UnsubscribeFilterByID are also available for similar purposes

If no options are specified when subscribing to a filter node, go-waku will automatically choose the peer to subscribe to. This behaviour can be controlled via options:

Options

• filter.WithPeer(peerID) - use an specific peer ID (which should be part of the node peerstore) to receive the messages from
• filter.WithAutomaticPeerSelection(host) - automatically select a peer that supports filter protocol from the peerstore to receive the messages from
• filter.WithFastestPeerSelection(ctx) - automatically select a peer based on its ping reply time