feat(mix): cover traffic with constant rate

- Integrate ConstantRateCoverTraffic from libp2p mix module with default
  totalSlots = userMessageLimit (or 2) and 10s epoch
- Add --mix-user-message-limit and --mix-disable-spam-protection CLI flags
  with corresponding MixConfBuilder accessors and MixConf fields
- Wrap mixRlnSpamProtection construction so it is skipped when spam
  protection is disabled, with a nil guard in setupSpamProtectionCallbacks
- Add waku/common/option_shims.nim restoring valueOr/withValue templates
  for std/options (removed upstream by results), and import it across
  modules that relied on the old behavior
- Sink chat2mix logs to textlines (stdout) instead of textlines[file] to
  work around a chronicles compile-time macro-eval bug under Nim 2.2.4
- Rename ExtendedKademliaDiscoveryParams -> ExtendedServiceDiscoveryParams
  to match the kad_disco -> service_discovery rename in nim-libp2p
- Bump nim-libp2p to e1bbda4f6 (PR #2243 "cover traffic with constant
  rate") and mix-rln-spam-protection-plugin to 153d0c0 (PR #5 cover
  traffic epoch change support); both pre-libp2p_mix-extraction
- Add simulations/mixnet/check_cover_traffic.sh for monitoring
  mix_cover_* / mix_slot_* metrics, plus per-node cover-traffic configs

simulations/mixnet/README.md

@@ -24,6 +24,7 @@ The simulation includes:
 | `run_chat_mix.sh`  | Chat app instance 1                        |
 | `run_chat_mix1.sh` | Chat app instance 2                        |
 | `build_setup.sh`   | Build and generate RLN credentials         |
+| `check_cover_traffic.sh` | Monitor cover traffic metrics from all nodes |
 
 ## Prerequisites
 
@@ -130,3 +131,35 @@ To exit the chat apps, enter `/exit`:
 >> /exit
 quitting...
 ```
+
+## Running Without DoS Protection
+
+To test cover traffic without RLN spam protection (avoids heavy proof generation compute), the config files include two flags:
+
+```toml
+mix-user-message-limit=2        # slots per epoch (reduce for lighter testing)
+mix-disable-spam-protection=true # skip RLN proof generation/verification
+```
+
+These are already set in `config.toml` through `config4.toml`. To re-enable RLN, set `mix-disable-spam-protection=false` (or remove the line) and ensure credentials are generated via `./build_setup.sh`.
+
+When running without DoS protection, cover traffic uses an internal epoch timer and does not require RLN credentials or `rln_tree.db`.
+
+### Monitoring Cover Traffic
+
+Use the metrics script to verify cover traffic is working:
+
+```bash
+./check_cover_traffic.sh
+```
+
+Key metrics to look for:
+- `mix_cover_emitted_total` — cover messages generated per node (should increase each epoch)
+- `mix_cover_received_total` — cover messages received back at origin after 3-hop mix path
+- `mix_slots_exhausted_total` — expected when slots per epoch are low
+
+### Note on Rate Limit and Expected Errors
+
+The default `mix-user-message-limit=2` (R=2) with path length L=3 yields a fractional cover target of `R/(1+L) = 0.5` packets per epoch. Because this is not an integer, epoch boundary jitter can cause two cover emissions in one epoch, exhausting all slots and leaving none for forwarding. This produces `SLOT_EXHAUSTED` and `SPAM_PROOF_GEN_FAILED` errors at intermediate hops — these are expected with the default config.
+
+For a clean setup, R should be a multiple of `(1+L) = 4`. Setting `mix-user-message-limit=4` gives exactly 1 cover packet per epoch with 3 slots remaining for forwarding, eliminating these errors.

simulations/mixnet/check_cover_traffic.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+# Check cover traffic metrics from all mix nodes.
+# Ports: 8008 + ports-shift (1-5) = 8009-8013
+
+echo "=== Cover Traffic Metrics ==="
+echo ""
+
+for i in 1 2 3 4 5; do
+  port=$((8008 + i))
+  echo "--- Node $i (port $port) ---"
+  metrics=$(curl -s "http://127.0.0.1:$port/metrics" 2>/dev/null)
+  if [ -z "$metrics" ]; then
+    echo "  (unreachable)"
+  else
+    echo "$metrics" | grep -E "mix_cover_|mix_slot_" | grep -v "^#" || echo "  (no cover metrics yet)"
+  fi
+  echo ""
+done

simulations/mixnet/config.toml

@@ -7,6 +7,7 @@ lightpush = true
 max-connections = 150
 peer-exchange = false
 metrics-logging = false
+metrics-server = true
 cluster-id = 2
 discv5-discovery = false
 discv5-udp-port = 9000
@@ -26,3 +27,5 @@ nat = "extip:127.0.0.1"
 ext-multiaddr = ["/ip4/127.0.0.1/tcp/60001"]
 ext-multiaddr-only = true
 ip-colocation-limit=0
+mix-user-message-limit=4
+mix-disable-spam-protection=false

simulations/mixnet/config1.toml

@@ -7,6 +7,7 @@ lightpush = true
 max-connections = 150
 peer-exchange = false
 metrics-logging = false
+metrics-server = true
 cluster-id = 2
 discv5-discovery = false
 discv5-udp-port = 9001
@@ -27,4 +28,6 @@ nat = "extip:127.0.0.1"
 ext-multiaddr = ["/ip4/127.0.0.1/tcp/60002"]
 ext-multiaddr-only = true
 ip-colocation-limit=0
+mix-user-message-limit=4
+mix-disable-spam-protection=false
 #staticnode = ["/ip4/127.0.0.1/tcp/60001/p2p/16Uiu2HAmPiEs2ozjjJF2iN2Pe2FYeMC9w4caRHKYdLdAfjgbWM6o", "/ip4/127.0.0.1/tcp/60003/p2p/16Uiu2HAmTEDHwAziWUSz6ZE23h5vxG2o4Nn7GazhMor4bVuMXTrA","/ip4/127.0.0.1/tcp/60004/p2p/16Uiu2HAmPwRKZajXtfb1Qsv45VVfRZgK3ENdfmnqzSrVm3BczF6f","/ip4/127.0.0.1/tcp/60005/p2p/16Uiu2HAmRhxmCHBYdXt1RibXrjAUNJbduAhzaTHwFCZT4qWnqZAu"]

simulations/mixnet/config2.toml

@@ -7,6 +7,7 @@ lightpush = true
 max-connections = 150
 peer-exchange = false
 metrics-logging = false
+metrics-server = true
 cluster-id = 2
 discv5-discovery = false
 discv5-udp-port = 9002
@@ -27,4 +28,6 @@ nat = "extip:127.0.0.1"
 ext-multiaddr = ["/ip4/127.0.0.1/tcp/60003"]
 ext-multiaddr-only = true
 ip-colocation-limit=0
+mix-user-message-limit=4
+mix-disable-spam-protection=false
 #staticnode = ["/ip4/127.0.0.1/tcp/60001/p2p/16Uiu2HAmPiEs2ozjjJF2iN2Pe2FYeMC9w4caRHKYdLdAfjgbWM6o", "/ip4/127.0.0.1/tcp/60002/p2p/16Uiu2HAmLtKaFaSWDohToWhWUZFLtqzYZGPFuXwKrojFVF6az5UF","/ip4/127.0.0.1/tcp/60004/p2p/16Uiu2HAmPwRKZajXtfb1Qsv45VVfRZgK3ENdfmnqzSrVm3BczF6f","/ip4/127.0.0.1/tcp/60005/p2p/16Uiu2HAmRhxmCHBYdXt1RibXrjAUNJbduAhzaTHwFCZT4qWnqZAu"]

simulations/mixnet/config3.toml

@@ -7,6 +7,7 @@ lightpush = true
 max-connections = 150
 peer-exchange = false
 metrics-logging = false
+metrics-server = true
 cluster-id = 2
 discv5-discovery = false
 discv5-udp-port = 9003
@@ -27,4 +28,6 @@ nat = "extip:127.0.0.1"
 ext-multiaddr = ["/ip4/127.0.0.1/tcp/60004"]
 ext-multiaddr-only = true
 ip-colocation-limit=0
+mix-user-message-limit=4
+mix-disable-spam-protection=false
 #staticnode = ["/ip4/127.0.0.1/tcp/60002/p2p/16Uiu2HAmLtKaFaSWDohToWhWUZFLtqzYZGPFuXwKrojFVF6az5UF", "/ip4/127.0.0.1/tcp/60003/p2p/16Uiu2HAmTEDHwAziWUSz6ZE23h5vxG2o4Nn7GazhMor4bVuMXTrA","/ip4/127.0.0.1/tcp/60001/p2p/16Uiu2HAmPiEs2ozjjJF2iN2Pe2FYeMC9w4caRHKYdLdAfjgbWM6o","/ip4/127.0.0.1/tcp/60005/p2p/16Uiu2HAmRhxmCHBYdXt1RibXrjAUNJbduAhzaTHwFCZT4qWnqZAu"]

simulations/mixnet/config4.toml

@@ -7,6 +7,7 @@ lightpush = true
 max-connections = 150
 peer-exchange = false
 metrics-logging = false
+metrics-server = true
 cluster-id = 2
 discv5-discovery = false
 discv5-udp-port = 9004
@@ -27,4 +28,6 @@ nat = "extip:127.0.0.1"
 ext-multiaddr = ["/ip4/127.0.0.1/tcp/60005"]
 ext-multiaddr-only = true
 ip-colocation-limit=0
+mix-user-message-limit=4
+mix-disable-spam-protection=false
 #staticnode = ["/ip4/127.0.0.1/tcp/60001/p2p/16Uiu2HAmPiEs2ozjjJF2iN2Pe2FYeMC9w4caRHKYdLdAfjgbWM6o", "/ip4/127.0.0.1/tcp/60003/p2p/16Uiu2HAmTEDHwAziWUSz6ZE23h5vxG2o4Nn7GazhMor4bVuMXTrA","/ip4/127.0.0.1/tcp/60004/p2p/16Uiu2HAmPwRKZajXtfb1Qsv45VVfRZgK3ENdfmnqzSrVm3BczF6f","/ip4/127.0.0.1/tcp/60002/p2p/16Uiu2HAmLtKaFaSWDohToWhWUZFLtqzYZGPFuXwKrojFVF6az5UF"]

simulations/mixnet/setup_credentials.nim

@@ -20,8 +20,8 @@ import
 
 const
   KeystorePassword = "mix-rln-password" # Must match protocol.nim
-  DefaultUserMessageLimit = 100'u64 # Network-wide default rate limit
+  DefaultUserMessageLimit = 4'u64 # R=4 slots per 10s epoch
-  SpammerUserMessageLimit = 3'u64 # Lower limit for spammer testing
+  SpammerUserMessageLimit = 3'u64 # Higher limit for spammer testing
 
   # Peer IDs derived from nodekeys in config files
   # config.toml:   nodekey = "f98e3fba96c32e8d1967d460f1b79457380e1a895f7971cecc8528abe733781a"

tools/confutils/cli_args.nim

@@ -642,6 +642,18 @@ with the drawback of consuming some more bandwidth.""",
       name: "mixnode"
     .}: seq[MixNodePubInfo]
 
+    mixUserMessageLimit* {.
+      desc:
+        "Maximum messages per RLN epoch for mix cover traffic. If not set, uses plugin default.",
+      name: "mix-user-message-limit"
+    .}: Option[int]
+
+    mixDisableSpamProtection* {.
+      desc: "Disable RLN spam protection for mix protocol (for testing only).",
+      defaultValue: false,
+      name: "mix-disable-spam-protection"
+    .}: bool
+
     # Kademlia Discovery config
     enableKadDiscovery* {.
       desc:
@@ -1079,6 +1091,9 @@ proc toWakuConf*(n: WakuNodeConf): ConfResult[WakuConf] =
   b.withMix(n.mix)
   if n.mixkey.isSome():
     b.mixConf.withMixKey(n.mixkey.get())
+  if n.mixUserMessageLimit.isSome():
+    b.mixConf.withUserMessageLimit(n.mixUserMessageLimit.get())
+  b.mixConf.withDisableSpamProtection(n.mixDisableSpamProtection)
 
   b.filterServiceConf.withEnabled(n.filter)
   b.filterServiceConf.withSubscriptionTimeout(n.filterSubscriptionTimeout)

waku/factory/conf_builder/mix_conf_builder.nim

@@ -12,6 +12,8 @@ type MixConfBuilder* = object
   enabled: Option[bool]
   mixKey: Option[string]
   mixNodes: seq[MixNodePubInfo]
+  userMessageLimit: Option[int]
+  disableSpamProtection: bool
 
 proc init*(T: type MixConfBuilder): MixConfBuilder =
   MixConfBuilder()
@@ -25,6 +27,12 @@ proc withMixKey*(b: var MixConfBuilder, mixKey: string) =
 proc withMixNodes*(b: var MixConfBuilder, mixNodes: seq[MixNodePubInfo]) =
   b.mixNodes = mixNodes
 
+proc withUserMessageLimit*(b: var MixConfBuilder, limit: int) =
+  b.userMessageLimit = some(limit)
+
+proc withDisableSpamProtection*(b: var MixConfBuilder, disable: bool) =
+  b.disableSpamProtection = disable
+
 proc build*(b: MixConfBuilder): Result[Option[MixConf], string] =
   if not b.enabled.get(false):
     return ok(none[MixConf]())
@@ -33,11 +41,27 @@ proc build*(b: MixConfBuilder): Result[Option[MixConf], string] =
       let mixPrivKey = intoCurve25519Key(ncrutils.fromHex(b.mixKey.get()))
       let mixPubKey = public(mixPrivKey)
       return ok(
-        some(MixConf(mixKey: mixPrivKey, mixPubKey: mixPubKey, mixNodes: b.mixNodes))
+        some(
+          MixConf(
+            mixKey: mixPrivKey,
+            mixPubKey: mixPubKey,
+            mixNodes: b.mixNodes,
+            userMessageLimit: b.userMessageLimit,
+            disableSpamProtection: b.disableSpamProtection,
+          )
+        )
       )
     else:
       let (mixPrivKey, mixPubKey) = generateKeyPair().valueOr:
         return err("Generate key pair error: " & $error)
       return ok(
-        some(MixConf(mixKey: mixPrivKey, mixPubKey: mixPubKey, mixNodes: b.mixNodes))
+        some(
+          MixConf(
+            mixKey: mixPrivKey,
+            mixPubKey: mixPubKey,
+            mixNodes: b.mixNodes,
+            userMessageLimit: b.userMessageLimit,
+            disableSpamProtection: b.disableSpamProtection,
+          )
+        )
       )

waku/factory/node_factory.nim

@@ -164,7 +164,12 @@ proc setupProtocols(
   #mount mix
   if conf.mixConf.isSome():
     let mixConf = conf.mixConf.get()
-    (await node.mountMix(conf.clusterId, mixConf.mixKey, mixConf.mixnodes)).isOkOr:
+    (
+      await node.mountMix(
+        conf.clusterId, mixConf.mixKey, mixConf.mixnodes, mixConf.userMessageLimit,
+        mixConf.disableSpamProtection,
+      )
+    ).isOkOr:
       return err("failed to mount waku mix protocol: " & $error)
 
   # Setup extended kademlia discovery

waku/factory/waku_conf.nim

@@ -51,6 +51,8 @@ type MixConf* = ref object
   mixKey*: Curve25519Key
   mixPubKey*: Curve25519Key
   mixnodes*: seq[MixNodePubInfo]
+  userMessageLimit*: Option[int]
+  disableSpamProtection*: bool
 
 type KademliaDiscoveryConf* = object
   bootstrapNodes*: seq[(PeerId, seq[MultiAddress])]

waku/node/waku_node.nim

@@ -317,6 +317,7 @@ proc mountMix*(
     mixPrivKey: Curve25519Key,
     mixnodes: seq[MixNodePubInfo],
     userMessageLimit: Option[int] = none(int),
+    disableSpamProtection: bool = false,
 ): Future[Result[void, string]] {.async.} =
   info "mounting mix protocol", nodeId = node.info #TODO log the config used
 
@@ -349,7 +350,7 @@ proc mountMix*(
 
   node.wakuMix = WakuMix.new(
     localaddrStr, node.peerManager, clusterId, mixPrivKey, mixnodes, publishMessage,
-    userMessageLimit,
+    userMessageLimit, disableSpamProtection,
   ).valueOr:
     error "Waku Mix protocol initialization failed", err = error
     return

waku/waku_mix/protocol.nim

@@ -11,6 +11,7 @@ import
   libp2p_mix/mix_metrics,
   libp2p_mix/delay_strategy,
   libp2p_mix/spam_protection,
+  libp2p_mix/cover_traffic,
   libp2p/[multiaddress, multicodec, peerid, peerinfo],
   eth/common/keys
 
@@ -91,6 +92,7 @@ proc new*(
     bootnodes: seq[MixNodePubInfo],
     publishMessage: PublishMessage,
     userMessageLimit: Option[int] = none(int),
+    disableSpamProtection: bool = false,
 ): WakuMixResult[T] =
   let mixPubKey = public(mixPrivKey)
   trace "mixPubKey", mixPubKey = mixPubKey
@@ -101,36 +103,50 @@ proc new*(
     peermgr.switch.peerInfo.publicKey.skkey, peermgr.switch.peerInfo.privateKey.skkey,
   )
 
-  # Initialize spam protection with persistent credentials
+  let totalSlots = userMessageLimit.get(2)
-  # Use peerID in keystore path so multiple peers can run from same directory
+  let ct = ConstantRateCoverTraffic.new(
-  # Tree path is shared across all nodes to maintain the full membership set
+    totalSlots = totalSlots,
-  let peerId = peermgr.switch.peerInfo.peerId
+    epochDuration = 10.seconds,
-  var spamProtectionConfig = defaultConfig()
+    useInternalEpochTimer = disableSpamProtection,
-  spamProtectionConfig.keystorePath = "rln_keystore_" & $peerId & ".json"
+  )
-  spamProtectionConfig.keystorePassword = "mix-rln-password"
-  if userMessageLimit.isSome():
-    spamProtectionConfig.userMessageLimit = userMessageLimit.get()
-  # rlnResourcesPath left empty to use bundled resources (via "tree_height_/" placeholder)
 
-  let spamProtection = newMixRlnSpamProtection(spamProtectionConfig).valueOr:
+  var spamProtectionOpt = default(Opt[SpamProtection])
-    return err("failed to create spam protection: " & error)
+  if not disableSpamProtection:
+    # Initialize spam protection with persistent credentials
+    let peerId = peermgr.switch.peerInfo.peerId
+    var spamProtectionConfig = defaultConfig()
+    spamProtectionConfig.keystorePath = "rln_keystore_" & $peerId & ".json"
+    spamProtectionConfig.keystorePassword = "mix-rln-password"
+    if userMessageLimit.isSome():
+      spamProtectionConfig.userMessageLimit = userMessageLimit.get()
+
+    let spamProtection = newMixRlnSpamProtection(spamProtectionConfig).valueOr:
+      return err("failed to create spam protection: " & error)
+    spamProtectionOpt = Opt.some(SpamProtection(spamProtection))
+  else:
+    info "mix spam protection disabled"
+
+  var mixRlnSpam: MixRlnSpamProtection
+  if spamProtectionOpt.isSome():
+    mixRlnSpam = MixRlnSpamProtection(spamProtectionOpt.get())
 
   var m = WakuMix(
     peerManager: peermgr,
     clusterId: clusterId,
     pubKey: mixPubKey,
-    mixRlnSpamProtection: spamProtection,
     publishMessage: publishMessage,
+    mixRlnSpamProtection: mixRlnSpam,
   )
   procCall MixProtocol(m).init(
     localMixNodeInfo,
     peermgr.switch,
-    spamProtection = Opt.some(SpamProtection(spamProtection)),
+    spamProtection = spamProtectionOpt,
     delayStrategy = Opt.some(
       DelayStrategy(
         ExponentialDelayStrategy.new(meanDelay = 100, rng = crypto.newRng())
       )
     ),
+    coverTraffic = Opt.some(CoverTraffic(ct)),
   )
 
   processBootNodes(bootnodes, peermgr, m)
@@ -147,6 +163,8 @@ proc setupSpamProtectionCallbacks(mix: WakuMix) =
   ## Set up the publish callback for spam protection coordination.
   ## This enables the plugin to broadcast membership updates and proof metadata
   ## via Waku relay.
+  if mix.mixRlnSpamProtection.isNil():
+    return
   if mix.publishMessage.isNil():
     warn "PublishMessage callback not available, spam protection coordination disabled"
     return