adds multi-transport example with ping

.gitignore

@@ -1,5 +1,6 @@
 mix_ping_tcp
 mix_ping_quic
+multiple_transports_example
 nimcache/
 nimbledeps/
 .agents/

multiple_transports_example.nim

@@ -0,0 +1,124 @@
+# SPDX-License-Identifier: MIT
+
+## Multiple Transports Example
+## 
+## This example demonstrates using multiple transport protocols (TCP and QUIC) 
+## with libp2p.
+## It creates a switch that listens on both TCP and QUIC addresses,
+## then performs ping operations preferring each transport protocol to
+## show how to use multiple transports in a libp2p application.
+
+{.used.}
+
+import chronos
+import std/[sequtils, strutils]
+import libp2p/[
+  builders,
+  crypto/crypto,
+  multiaddress,
+  peerid,
+  protocols/ping,
+  switch,
+]
+
+proc newTcpQuicSwitch*(
+    privKey: Opt[PrivateKey] = Opt.none(PrivateKey),
+    rng: ref HmacDrbgContext = newRng()
+): Switch =
+  ## A switch that listens on TCP and QUIC addresses.
+  let addrs = @[
+    MultiAddress.init("/ip4/0.0.0.0/udp/0/quic-v1").tryGet(),
+    MultiAddress.init("/ip4/0.0.0.0/tcp/0").tryGet(),
+  ]
+
+  var builder = SwitchBuilder
+    .new()
+    .withRng(rng)
+    .withAddresses(addrs)
+    .withNoise()
+    .withMplex()
+    .withQuicTransport()
+    .withTcpTransport()
+
+  privKey.withValue(key):
+    builder = builder.withPrivateKey(key)
+
+  builder.build()
+
+proc quicPreferred*(addrs: seq[MultiAddress]): seq[MultiAddress] =
+  ## Dial order is address order, so put QUIC addresses before fallback transports.
+  addrs.filterIt("/quic-v1" in $it) &
+    addrs.filterIt("/quic-v1" notin $it)
+
+proc tcpPreferred*(addrs: seq[MultiAddress]): seq[MultiAddress] =
+  ## Dial order is address order, so put TCP addresses before QUIC fallback.
+  addrs.filterIt("/quic-v1" notin $it) &
+    addrs.filterIt("/quic-v1" in $it)
+
+proc connectPreferringQuic*(
+    localSwitch: Switch, remotePeerId: PeerId, remoteAddrs: seq[MultiAddress]
+) {.async: (raises: [CancelledError, DialFailedError]).} =
+  await localSwitch.connect(remotePeerId, quicPreferred(remoteAddrs))
+
+proc pingPreferringQuic*(
+    localSwitch: Switch,
+    pingProtocol: Ping,
+    remotePeerId: PeerId,
+    remoteAddrs: seq[MultiAddress],
+): Future[Duration] {.
+    async: (raises: [CancelledError, DialFailedError, LPStreamError,
+      WrongPingAckError])
+.} =
+  let conn = await localSwitch.dial(remotePeerId, quicPreferred(remoteAddrs),
+  PingCodec)
+  defer:
+    await conn.close()
+
+  await pingProtocol.ping(conn)
+
+proc pingPreferringTcp*(
+    localSwitch: Switch,
+    pingProtocol: Ping,
+    remotePeerId: PeerId,
+    remoteAddrs: seq[MultiAddress],
+): Future[Duration] {.
+    async: (raises: [CancelledError, DialFailedError, LPStreamError,
+      WrongPingAckError])
+.} =
+  let conn = await localSwitch.dial(remotePeerId, tcpPreferred(remoteAddrs),
+    PingCodec)
+  defer:
+    await conn.close()
+
+  await pingProtocol.ping(conn)
+
+when isMainModule:
+  proc main() {.async: (raises: [CancelledError, LPError]).} =
+    let rng = newRng()
+    let pingProtocol = Ping.new(rng = rng)
+    let
+      quicClient = newTcpQuicSwitch(rng = rng)
+      tcpClient = newTcpQuicSwitch(rng = rng)
+      b = newTcpQuicSwitch(rng = rng)
+
+    b.mount(pingProtocol)
+
+    await quicClient.start()
+    await tcpClient.start()
+    await b.start()
+    defer:
+      await quicClient.stop()
+      await tcpClient.stop()
+      await b.stop()
+
+    let quicRtt = await quicClient.pingPreferringQuic(
+      pingProtocol, b.peerInfo.peerId, b.peerInfo.addrs
+    )
+    echo "quic ping: ", quicRtt
+
+    let tcpRtt = await tcpClient.pingPreferringTcp(
+      pingProtocol, b.peerInfo.peerId, b.peerInfo.addrs
+    )
+    echo "tcp ping: ", tcpRtt
+
+  waitFor main()