From b4d79b56305321d3e730766dd1d45bcc34441fd3 Mon Sep 17 00:00:00 2001
From: MrJack <36191829+biagiopietro@users.noreply.github.com>
Date: Mon, 24 Jun 2024 20:57:33 +0200
Subject: [PATCH] [multicast_dns] Optimized Socket Binding: Always bind to
0.0.0.0 for simplicity and efficiency - #79772 (#6700)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
I encountered this package long time ago (see linked issue below) and there were cases where it wasn't working.
After 3 years (yeah it's more time than expected) I managed to find the time to dust off `wireshark` and have look again.
# Preamble
Considering the following setup
Where Raspberry pi runs a `mDNS` service using the following `go`:
main.go
```go
package main
import (
"fmt"
"github.com/hashicorp/mdns"
"os"
"net/http"
)
func health(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(w, "ok")
}
func main() {
hostname, err := os.Hostname()
if err != nil {
panic(fmt.Sprintf("Error getting current hostname, description: %s", err.Error()))
}
info := []string{"mDNS get server"}
service, err := mdns.NewMDNSService(hostname, "_test._tcp", "", "", 8080, nil, info)
if err != nil {
panic(fmt.Sprintf("Error while exporting the service, description: %s", err.Error()))
}
server, err := mdns.NewServer(&mdns.Config{Zone: service})
if err != nil {
panic(fmt.Sprintf("Error while setting the discover server up, description: %s", err.Error()))
}
defer server.Shutdown()
http.HandleFunc("/", health)
http.ListenAndServe(":8081",nil)
}
```
client.dart
```dart
// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Example script to illustrate how to use the mdns package to discover the port
// of a Dart observatory over mDNS.
// ignore_for_file: avoid_print
import 'package:multicast_dns/multicast_dns.dart';
Future main() async {
// Parse the command line arguments.
const String name = '_test._tcp.local';
final MDnsClient client = MDnsClient();
// Start the client with default options.
await client.start();
// Get the PTR record for the service.
await for (final PtrResourceRecord ptr in client
.lookup(ResourceRecordQuery.serverPointer(name))) {
// Use the domainName from the PTR record to get the SRV record,
// which will have the port and local hostname.
// Note that duplicate messages may come through, especially if any
// other mDNS queries are running elsewhere on the machine.
await for (final SrvResourceRecord srv in client.lookup(
ResourceRecordQuery.service(ptr.domainName))) {
// Domain name will be something like "io.flutter.example@some-iphone.local._dartobservatory._tcp.local"
final String bundleId =
ptr.domainName; //.substring(0, ptr.domainName.indexOf('@'));
print('Dart observatory instance found at '
'${srv.target}:${srv.port} for "$bundleId".');
}
}
client.stop();
print('Done.');
}
```
multicast_dns.start() function
```dart
Future start({
InternetAddress? listenAddress,
NetworkInterfacesFactory? interfacesFactory,
int mDnsPort = mDnsPort,
InternetAddress? mDnsAddress,
}) async {
listenAddress ??= InternetAddress.anyIPv4;
interfacesFactory ??= allInterfacesFactory;
assert(listenAddress.address == InternetAddress.anyIPv4.address ||
listenAddress.address == InternetAddress.anyIPv6.address);
if (_started || _starting) {
return;
}
_starting = true;
final int selectedMDnsPort = _mDnsPort = mDnsPort;
_mDnsAddress = mDnsAddress;
// Listen on all addresses.
final RawDatagramSocket incoming = await _rawDatagramSocketFactory(
listenAddress.address,
selectedMDnsPort,
reuseAddress: true,
reusePort: true,
ttl: 255,
);
_mDnsAddress ??= incoming.address.type == InternetAddressType.IPv4
? mDnsAddressIPv4
: mDnsAddressIPv6;
final List interfaces =
(await interfacesFactory(listenAddress.type)).toList();
for (final NetworkInterface interface in interfaces) {
// Create a socket for sending on each adapter.
final InternetAddress targetAddress = interface.addresses[0];
// Join multicast on this interface.
incoming.joinMulticast(_mDnsAddress!, interface);
}
// Can't send to IPv6 any address.
if (incoming.address != InternetAddress.anyIPv6) {
_sockets.add(incoming);
} else {
_toBeClosed.add(incoming);
}
incoming.listen((RawSocketEvent event) => _handleIncoming(event, incoming));
_started = true;
_starting = false;
}
```