mDNS in Fuchsia

2023年6月30日 238次阅读 来源: 毒舌Ken

Fuchsia client network 相关模块现在只有如下几种，实现语言也很诡异。

dhcp             Rust
http_client      Rust
mdns             C++
netstack         Go
netstack3        Rust

猜测 Fuchsia 会重度使用 mDNS(multicast DNS)，所以完成度比较高。苹果系统(Bonjour)重度使用了mDNS。Fuchsia 里缺省配置可能是：

{
  "port": 5356,
  "v4_multicast_address": "224.0.0.250",
  "publications": [
    {
        "service": "_fuchsia._udp.",
        "port": 5356,
        "perform_probe": false
    }
  ]
}

mDNS封装简洁明了，提供的接口或抽象(fidl, mdns-util)有 ServiceSubscriber， ServiceInstance，PublicationResponder，Publication。要求

<host_name> and <instance_name> cannot end in '.'
<service_name> must start with '_' and end in '._tcp.' or '._udp.'

mdns-util 比起 dns-sd (Bonjour的工具)好用太多、简单太多。

由于 mDNS 本身不太复杂，索性翻了一下整个开发变更历史，感想放在了最后。

变更历史

2013年加入 chromium 的代码结构为：

net/dns/mdns_client.cc
...
net/dns/mdns_client_impl.cc
net/dns/mdns_client.h

2017/4/17 加入 packet reader/writer，目录结构大概如下:

bin/netconnector/BUILD.gn
bin/netconnector/mdns/dns_message.c
bin/netconnector/mdns/packet_reader.cc
bin/netconnector/mdns/packet_writer.cc
bin/netconnector/mdns/dns_formatting.cc
bin/netconnector/mdns/dns_reading.cc
bin/netconnector/mdns/dns_writing.cc
public/lib/netconnector/fidl/mdns.fidl

2017/4/21 开始加入 MdnsNames/Transceiver

2017/4/26 开始加入 AddressResponder / client(mdns.fidl)

2017/4/28 开始加入 service implementation

bin/netconnector/mdns/dns_formatting.cc
bin/netconnector/mdns/mdns_addresses.cc
public/lib/netconnector/fidl/mdns.fidl

中间还有几次全局路径调整, media path 变更，ftl to fxl

2017/9/14 clang format

2017/9/26 recheck NICs when address family is unspecified

2017/10/4 delete unused netconfig.h from the include list

2017/10/12 迎来mDNS的一次大更新

2017/10/13 add MdnsService.AddResponder

2017/10/16 add ‘mdns’ tool

2017/10/16 add ‘mdns’ tool

2017/10/19 simplify mDNS question/resource send logic

2017/10/20 simplify mDNS agents using base class

2017/10/23 implement mDNS unicast response

2017/10/24 postpone distribution of host name

2017/10/26 implement address probe

2017/10/27 publish _fuchsia._tcp. instance by unique name
add service instance probing

2017/11/14 Sandbox mdns.开始加入

packages/mdns

2017/12/4 fix potential DOS exploit in DNS name parsing

2017/12/4 NET-268 use netstack RegisterListener

2017/12/4 fix potential DOS exploit in DNS name parsing

2018/1/12 move mdns tool to bin/mdns/tool from bin/mdns

bin/mdns/{ => tool}/BUILD.gn

2018/1/16 add public/lib/mdns files

public/lib/mdns/cpp/BUILD.gn
public/lib/mdns/cpp/service_subscriber.cc
public/lib/mdns/fidl/mdns.fidl

2018/1/16 update mdns command line tool to use new lib

2018/1/16 mdns 从 netconnector 独立成为一个Service

bin/{netconnector/mdns => mdns/service}/dns_formatting.cc

目录结构变更为

bin/mdns/service/mdns_service_impl.cc
bin/mdns/service/dns_formatting.cc
bin/mdns/tool/mdns_impl.cc
public/lib/mdns/cpp/service_subscriber.cc

2018/1/24 factor out interface enumeration

2018/1/26 change the non-fidl publication model

2018/1/24 add standalone mdns app (mdns_standalone)

bin/mdns/standalone/BUILD.gn

2018/1/29 add traffic reporting to mdns

2018/1/30 Update FIDL1 C++ bindings to match FIDL2 interface

2018/1/30 eliminate awkward host name dataflow

2018/2/5 handle socket init failures on address change

2018/2/7 simplify address fixup logic (and fix bug)

2018/2/12 add cpu and memory reporting to mdns_standalone

2018/2/13 Add Rust wrappers for mdns fidl service

public/rust/fidl_crates/garnet_public_lib_mdns_fidl/src/lib.rs

2018/2/12 Add beginnings of mDNS lib.

system/ulib/mdns/mdns.c

2018/2/23 Rename fidl namespace to f1dl 这个更新很诡异

2018/3/22 Make mdns tool build

bin/mdns/tool/mdns_impl.cc
public/lib/mdns/fidl/BUILD.gn

2018/3/22 Make mdns_service build

bin/mdns/service/mdns.cc

2018/3/29 Add method to add authorities to a message.

system/ulib/mdns/mdns.c

2018/4/6 remove deprecated TaskRunner/MessageLoop

2018/5/18 filter out messages from the local address

2018/6/1 Port to fit::function.

2018/6/4 git-file-format bin/mdns

2018/6/4 change fidl namespace to fuchsia.mdns

2018/6/9 use fostr formatting library

2018/8/3 reject 0.0.0.0 addresses

2018/9/28 update service configuration

2018/10/12 register mdns_service and start it in garnet default

至此 mDNS 算是正式投入使用了

2018/11/1 add mdns_service to packages/framework, add LegacySocketProvider to mdns_service’s sandbox

2018/11/1 remove mdns code.

system/ulib/mdns/mdns.c

2018/11/1 remove mdns_standalone

bin/mdns/standalone/main.cc

2018/11/1 rename mdns_service->mdns, mdns->mdns_util

bin/mdns/{tool => util}/BUILD.gn
bin/mdns/{tool => util}/main.cc

2018/11/6 respond to wildcard queries

2018/11/8 enable support for V6 addresses

2018/11/29 fix name compression exploit

fuzzer/manually tested using avahi

2018/11/8 enable support for V6 addresses

2018/12/6 publish the device as ‘_fuchsia._udp.’ by default

2018/12/10 Add bin/dev_finder command

bin/dev_finder/list.go

2018/12/13 remove raw new/delete

2018/12/20 Add fuzzer for PacketReader.

2019/1/2 fix address fix-up to enable V6

2019/1/3 use gethostname for faster startup

2019/1/8 make mdns_util a shell binary

bin/mdns/util/BUILD.gn

2019/1/22 adapt to new socket option behavior

2019/1/22 support V6 addresses on non-V4-provisioned NICs

2019/1/23 rename mdns_util to mdns-util

2019/2/12 set mdns sdk category to partner

2019/2/22 use strerror to format errno values in logs

2019/3/10 remove IP_MULTICAST_LOOP workaround/set IP{,V6}_MULTICAST_LOOP = 0

2019/3/26 update handling of setsockopt and bind errors

2019/4/8 FIDL readability improvements

2019/4/16 reviewed FIDL definition for fuchsia.net.mdns

2019/4/18 support config files

2019/4/23 Switch default port for mDNS responder to 5356

2019/4/29 add v4/v6_multicast_address properties to config

2019/4/30 transition to new fuchsia.net.mdns FIDL API

2019/5/1 move mdns implementation from garnet/bin to src

{garnet/bin => src/connectivity/network}/mdns/BUILD.gn

至此目录结构变为

src/connectivity/network/mdns/BUILD.gn
                             service/BUILD.gn
                             service/dns_formatting.cc
                             service/main.cc
                             test/dns_names_test.cc
                             util/mdns_impl.cc
                             util/main.cc

2019/5/2 change the multicast V4 address to 224.0.0.250

2019/6/7 move all mdns package targets out of garnet

感想

  • 代码基于 Chromium 开始，即使差异如此的大
  • 该模块未提前开发，等待核心稳定后才开始
  • 2017年4月 才算开始开发，2018年10月稳定后集成，花费时间比我想象的多
  • 大致流程是：开始、主体趋于稳定、集成、fuzzer 和测试，然后正常迭代
  • 这个模块有固定的工程师，但是其他人也在小规模改动
  • 至少使用了Avahi(mDNS 的 posix 实现) 的测试用例
  • 文件名一定是下划线，但是名称会使用连字符 (符合本人口味)
  • 大规模目录结构调整出现了很多次，关于 C++ 的使用规则调整也出现了至少2次
    原文作者：毒舌Ken
    原文地址: https://zhuanlan.zhihu.com/p/68570555
    本文转自网络文章，转载此文章仅为分享知识，如有侵权，请联系博主进行删除。
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