feat: example using filter and lightpush (#1720)

* feat: add filter-lightpush example

* chore: examples/v2/filter_subscriber.nim

Co-authored-by: Ivan Folgueira Bande <128452529+Ivansete-status@users.noreply.github.com>

* chore: update examples/v2/filter_subscriber.nim

Co-authored-by: Ivan Folgueira Bande <128452529+Ivansete-status@users.noreply.github.com>

---------

Co-authored-by: Ivan Folgueira Bande <128452529+Ivansete-status@users.noreply.github.com>

examples/v2/README.md

@@ -4,7 +4,7 @@ TODO
 
 # publisher/subscriber
 
-Within `examples/v2` you can find a `publisher` and a `subscriber`. The first one publises messages to the default pubsub topic to a given content topic, and the second one runs forever listening to that pubsub topic and printing the content it receives.
+Within `examples/v2` you can find a `publisher` and a `subscriber`. The first one publishes messages to the default pubsub topic on a given content topic, and the second one runs forever listening to that pubsub topic and printing the content it receives.
 
 **Some notes:**
 * These examples are meant to work even in if you are behind a firewall and you can't be discovered by discv5.
@@ -32,3 +32,33 @@ And run a publisher
 ```
 
 See how the subscriber received the messages published by the publisher. Feel free to experiment from different machines in different locations.
+
+# resource-restricted publisher/subscriber (lightpush/filter)
+
+To illustrate publishing and receiving messages on a resource-restricted client,
+`examples/v2` also provides a `lightpush_publisher` and a `filter_subscriber`.
+The `lightpush_publisher` continually publishes messages via a lightpush service node
+to the default pubsub topic on a given content topic.
+The `filter_subscriber` subscribes via a filter service node
+to the same pubsub and content topic.
+It runs forever, maintaining this subscription
+and printing the content it receives.
+
+**compile and run:**
+
+Wait until the filter subscriber is ready.
+```console
+./env.sh bash
+nim c -r examples/v2/filter_subscriber.nim
+```
+
+And run a lightpush publisher
+```console
+./env.sh bash
+nim c -r examples/v2/lightpush_publisher.nim
+```
+
+See how the filter subscriber receives messages published by the lightpush publisher.
+Neither the publisher nor the subscriber participates in `relay`,
+but instead make use of service nodes to save resources.
+Feel free to experiment from different machines in different locations.

examples/v2/filter_subscriber.nim

@@ -0,0 +1,82 @@
+## Example showing how a resource restricted client may
+## subscribe to messages without relay
+
+import
+  chronicles,
+  chronos,
+  stew/byteutils,
+  stew/results
+import
+  ../../../waku/common/logging,
+  ../../../waku/v2/node/peer_manager,
+  ../../../waku/v2/waku_core,
+  ../../../waku/v2/waku_filter_v2/client
+
+const
+  FilterPeer = "/ip4/104.154.239.128/tcp/30303/p2p/16Uiu2HAmJb2e28qLXxT5kZxVUUoJt72EMzNGXB47Rxx5hw3q4YjS" # node-01.gc-us-central1-a.wakuv2.test.statusim.net on wakuv2.test
+  FilterPubsubTopic = PubsubTopic("/waku/2/default-waku/proto")
+  FilterContentTopic = ContentTopic("/examples/1/light-pubsub-example/proto")
+
+proc unsubscribe(wfc: WakuFilterClient,
+                 filterPeer: RemotePeerInfo,
+                 filterPubsubTopic: PubsubTopic,
+                 filterContentTopic: ContentTopic) {.async.} =
+  notice "unsubscribing from filter"
+  let unsubscribeRes = await wfc.unsubscribe(filterPeer, filterPubsubTopic, @[filterContentTopic])
+  if unsubscribeRes.isErr:
+    notice "unsubscribe request failed", err=unsubscribeRes.error
+  else:
+    notice "unsubscribe request successful"
+
+proc messagePushHandler(pubsubTopic: PubsubTopic, message: WakuMessage) =
+  let payloadStr = string.fromBytes(message.payload)
+  notice "message received", payload=payloadStr,
+                             pubsubTopic=pubsubTopic,
+                             contentTopic=message.contentTopic,
+                             timestamp=message.timestamp
+
+proc maintainSubscription(wfc: WakuFilterClient,
+                          filterPeer: RemotePeerInfo,
+                          filterPubsubTopic: PubsubTopic,
+                          filterContentTopic: ContentTopic) {.async.} =
+  while true:
+    notice "maintaining subscription"
+    # First use filter-ping to check if we have an active subscription
+    let pingRes = await wfc.ping(filterPeer)
+    if pingRes.isErr():
+      # No subscription found. Let's subscribe.
+      notice "no subscription found. Sending subscribe request"
+
+      let subscribeRes = await wfc.subscribe(filterPeer, filterPubsubTopic, @[filterContentTopic])
+
+      if subscribeRes.isErr():
+        notice "subscribe request failed. Quitting.", err=subscribeRes.error
+        break
+      else:
+        notice "subscribe request successful."
+    else:
+      notice "subscription found."
+
+    await sleepAsync(60.seconds) # Subscription maintenance interval
+
+proc setupAndSubscribe(rng: ref HmacDrbgContext) =
+  let filterPeer = parsePeerInfo(FilterPeer).get()
+
+  setupLogLevel(logging.LogLevel.NOTICE)
+  notice "starting filter subscriber"
+
+  var
+    switch = newStandardSwitch()
+    pm = PeerManager.new(switch)
+    wfc = WakuFilterClient.new(rng, messagePushHandler, pm)
+
+  # Mount filter client protocol
+  switch.mount(wfc)
+
+  # Start maintaining subscription
+  asyncSpawn maintainSubscription(wfc, filterPeer, FilterPubsubTopic, FilterContentTopic)
+
+when isMainModule:
+  let rng = newRng()
+  setupAndSubscribe(rng)
+  runForever()

examples/v2/lightpush_publisher.nim

@@ -0,0 +1,57 @@
+## Example showing how a resource restricted client may
+## use lightpush to publish messages without relay
+
+import
+  chronicles,
+  chronos,
+  stew/byteutils,
+  stew/results
+import
+  ../../../waku/common/logging,
+  ../../../waku/v2/node/peer_manager,
+  ../../../waku/v2/waku_core,
+  ../../../waku/v2/waku_lightpush/client
+
+const
+  LightpushPeer = "/ip4/134.209.139.210/tcp/30303/p2p/16Uiu2HAmPLe7Mzm8TsYUubgCAW1aJoeFScxrLj8ppHFivPo97bUZ" # node-01.do-ams3.wakuv2.test.statusim.net on wakuv2.test
+  LightpushPubsubTopic = PubsubTopic("/waku/2/default-waku/proto")
+  LightpushContentTopic = ContentTopic("/examples/1/light-pubsub-example/proto")
+
+proc publishMessages(wlc: WakuLightpushClient,
+                     lightpushPeer: RemotePeerInfo,
+                     lightpushPubsubTopic: PubsubTopic,
+                     lightpushContentTopic: ContentTopic) {.async.} =
+  while true:
+    let text = "hi there i'm a lightpush publisher"
+    let message = WakuMessage(payload: toBytes(text),               # content of the message
+                              contentTopic: lightpushContentTopic,  # content topic to publish to
+                              ephemeral: true,                      # tell store nodes to not store it
+                              timestamp: getNowInNanosecondTime())  # current timestamp
+
+    let wlpRes = await wlc.publish(lightpushPubsubTopic, message, lightpushPeer)
+
+    if wlpRes.isOk():
+      notice "published message using lightpush", message=message
+    else:
+      notice "failed to publish message using lightpush", err=wlpRes.error()
+
+    await sleepAsync(5000) # Publish every 5 seconds
+
+proc setupAndPublish(rng: ref HmacDrbgContext) =
+  let lightpushPeer = parsePeerInfo(LightpushPeer).get()
+
+  setupLogLevel(logging.LogLevel.NOTICE)
+  notice "starting lightpush publisher"
+
+  var
+    switch = newStandardSwitch()
+    pm = PeerManager.new(switch)
+    wlc = WakuLightpushClient.new(pm, rng)
+
+  # Start maintaining subscription
+  asyncSpawn publishMessages(wlc, lightpushPeer, LightpushPubsubTopic, LightpushContentTopic)
+
+when isMainModule:
+  let rng = newRng()
+  setupAndPublish(rng)
+  runForever()