adds mix example using QUIC transport

mix_ping_quic.nim

@@ -0,0 +1,141 @@
+# SPDX-License-Identifier: Apache-2.0 OR MIT
+
+## Mix Protocol Ping Example with QUIC Transport
+##
+## This example demonstrates using the Mix protocol with the Ping protocol.
+## It creates a set of mix nodes that form an anonymous overlay network,
+## then sends a ping through the mix network to a destination node and
+## receives the response via Single Use Reply Blocks (SURBs).
+## This example uses QUIC transport for all nodes.
+
+{.used.}
+
+import chronicles, chronos, results
+import std/[strformat, sequtils, sugar]
+import libp2p/[
+    protocols/mix,
+    protocols/mix/mix_protocol,
+    protocols/mix/curve25519,
+    protocols/ping,
+    peerid,
+    multiaddress,
+    switch,
+    builders,
+    crypto/crypto,
+    crypto/secp,
+  ]
+
+const NumMixNodes = 10
+
+proc generateLocalQuicMixNodeInfo(): MixNodeInfo =
+  let
+    (mixPrivKey, mixPubKey) = generateKeyPair().expect("Generate key pair error")
+    keyPair = SkKeyPair.random(newRng()[])
+    pubKeyProto = PublicKey(scheme: Secp256k1, skkey: keyPair.pubkey)
+
+  MixNodeInfo(
+    peerId: PeerId.init(pubKeyProto).expect("PeerId init error"),
+    multiAddr: MultiAddress.init(fmt"/ip4/0.0.0.0/udp/0/quic-v1").tryGet(),
+    mixPubKey: mixPubKey,
+    mixPrivKey: mixPrivKey,
+    libp2pPubKey: keyPair.pubkey,
+    libp2pPrivKey: keyPair.seckey,
+  )
+
+proc generateLocalQuicMixNodeInfos(count: int): seq[MixNodeInfo] =
+  var nodeInfos: seq[MixNodeInfo] = newSeq[MixNodeInfo](count)
+  for i in 0 ..< count:
+    nodeInfos[i] = generateLocalQuicMixNodeInfo()
+  nodeInfos
+
+proc createSwitch(
+    multiAddr: MultiAddress, libp2pPrivKey: Opt[SkPrivateKey] = Opt.none(SkPrivateKey)
+): Switch =
+  var rng = newRng()
+  let skkey = libp2pPrivKey.valueOr(SkKeyPair.random(rng[]).seckey)
+  let privKey = PrivateKey(scheme: Secp256k1, skkey: skkey)
+  newStandardSwitchBuilder(privKey = Opt.some(privKey), addrs = multiAddr, transport = TransportType.QUIC).build()
+
+
+proc mixPingSimulation() {.async: (raises: [Exception]).} =
+  let mixNodeInfos = generateLocalQuicMixNodeInfos(NumMixNodes)
+  var switches: seq[Switch] = @[]
+  var mixProtos: seq[MixProtocol] = @[]
+
+  # Start switches first so wildcard listen addresses are resolved to dialable addresses.
+  for nodeInfo in mixNodeInfos:
+    var switch = createSwitch(nodeInfo.multiAddr, Opt.some(nodeInfo.libp2pPrivKey))
+    await switch.start()
+    info "Mix node switch",
+      peerId = switch.peerInfo.peerId,
+      addrs = switch.peerInfo.addrs,
+      listenAddrs = switch.peerInfo.listenAddrs
+
+    switches.add(switch)
+  
+  defer:
+    await switches.mapIt(it.stop()).allFutures()
+
+  let resolvedInfos = collect:
+    for i, nodeInfo in mixNodeInfos:
+      initMixNodeInfo(
+        nodeInfo.peerId,
+        switches[i].peerInfo.addrs[0],
+        nodeInfo.mixPubKey,
+        nodeInfo.mixPrivKey,
+        nodeInfo.libp2pPubKey,
+        nodeInfo.libp2pPrivKey,
+      )
+  
+  # Mount Mix protocols using the resolved, dialable node addresses.
+  for i, nodeInfo in resolvedInfos:
+    var switch = switches[i]
+    let proto = MixProtocol.new(nodeInfo, switch)
+
+    await proto.start()
+
+    # Populate nodePool with all other nodes' public info
+    proto.nodePool.add(resolvedInfos.includeAllExcept(nodeInfo))
+
+    # Register how to read ping responses (32 bytes exactly)
+    proto.registerDestReadBehavior(PingCodec, readExactly(32))
+    switch.mount(proto)
+
+    mixProtos.add(proto)
+
+  # Create a destination node (not part of the mix network)
+  let destNode =
+    createSwitch(MultiAddress.init("/ip4/0.0.0.0/udp/0/quic-v1").tryGet())
+  defer:
+    await destNode.stop()
+
+  let pingProto = Ping.new()
+  destNode.mount(pingProto)
+
+  # Start destination switch after mounting Ping.
+  await destNode.start()
+
+  # Pick sender (first mix node) and send ping through the mix network
+  let senderIndex = 0
+
+  info "Sending ping through mix network",
+    sender = switches[senderIndex].peerInfo.peerId,
+    destination = destNode.peerInfo.peerId
+
+  # Create a connection through the mix network
+  let conn = mixProtos[senderIndex]
+    .toConnection(
+      MixDestination.init(destNode.peerInfo.peerId, destNode.peerInfo.addrs[0]),
+      PingCodec,
+      MixParameters(expectReply: Opt.some(true), numSurbs: Opt.some(byte(1))),
+    )
+    .expect("could not build connection")
+
+  # Send ping and wait for response through the mix network
+  let response = await pingProto.ping(conn)
+  await conn.close()
+
+  info "Ping response received through mix network", rtt = response
+
+when isMainModule:
+  waitFor(mixPingSimulation())