Hacker News Reader

Comment by giancarlostoro | Hacker News Reader

I'm a big fan of Zeroconf / MDNS / Avahi / Bonjour (it has many names due to the differing packages that can be used for it across platforms). It's a great way to make any type of service discoverable, whether it's a web service, or what have you. Having had used something like Eureka from Netflix I think mdns is way simpler, especially on Linux, if you can install Avahi all you need to do is write an XML file to a directory and you're broadcasting a service immediately.

View on HN

Zeroconf is fantastic for discovering services, but hardly anyone supports it. Apple removed it from Safari, 3 years ago [1]. It's been an open feature request in Chromium for 11 years [2], and in Firefox for 18 years [3].

The only major database I know which supports it is Postgres (it's disabled by default) [4]. On MySQL, it's an open work item, untouched for 13 years [5].

Last I checked, no major web framework broadcasts its service using Zeroconf.

Zeroconf service broadcast is so easy to implement (really) and such a tremendous help to users that I don't understand why developers aren't falling over themselves to implement it.

[1]: https://apple.stackexchange.com/questions/299700 [2]: https://bugs.chromium.org/p/chromium/issues/detail?id=13573 [3]: https://bugzilla.mozilla.org/show_bug.cgi?id=173804 [4]: https://www.postgresql.org/docs/9.1/runtime-config-connectio... [5]: https://dev.mysql.com/worklog/?sc=id&sd=ASC&pg=3

The browser support you listed is for listing out the available sites. The browsers still support mdns for name resolution. Zeroconf is used in Google Cast and Airplay for service discovery.

As Apple's Bonjour page points out, addressing and naming is only 2/3 of it. If that's all you support, then you still depend on users knowing the name, and typing it with no mistakes -- not exactly "zero configuration". 1980's AppleTalk was better than that.

How do browsers 'support mDNS for name resolution'? Isn't that a feature of the OS? I can "ping NAS.local" (without a DNS server) just as easily as I can go to "http://NAS.local", and ping.c doesn't appear to have any mDNS code.

Right there still a need for apps and browsers to surface mDNS services but the parent comment made it seem like the browsers can't use mDNS at all.

You're are correct, mDNS name resolution is an OS feature and to the browser/program/app it makes no difference.

Notably Android doesn't support mDNS as part of general hostname resolution. (There is the NSD API available but you have to explicitly use it, and the browsers do not.)

Apple removed the built-in display of _http._tcp. services. I don’t know why they chose to do this, but very few applications ever bothered to advertise this service. By far the most common use-case was for printer configuration UIs, which can be found specifically with the _printer._sub._http._tcp subtype. Apple’s print configuration UIs still expose a way to get to the printer web interface and this presumably uses _printer._sub._http._tcp.

Having said all that, I do wish Safari still supported it.

Yes I just wish microsoft hadn't complicated it with LLMNR.

All sorts of things use mDNS now (chromecast, spotify, printers, thermostats). And finally windows will start to support mDNS so hopefully we can finally settle on one good autodiscovery protocol and get rid of the horror that is SSDP.

I believe Microsoft finally added mdns to Windows 10, you might have to install it as a component yourself though. It's not yet available under Win32 though by the sound of it.

Here’s some documentation: https://docs.microsoft.com/en-us/uwp/api/Windows.Networking....

Lots of new core APIs added in Windows 10 aren’t available via Win32 even if they have nothing to do with packages, unfortunately. It’s extremely convoluted but you can use the Windows.Sdk, Contracts, or CsWinRT packages to interop with the WinRT APIs from a C++, C#, or now even rust application but depending on which APIs you consume you may need to use a Windows Application Project appx/msix wrapper to package your code and associate it with a package ID unlocking the APIs for use.

(I have a hello world project demonstrating a WPF .NET Core project hosting a custom control consisting of a single text block that displays your current location via the Geolocator API and it requires four different individually user-created projects in the Visual Studio solution and a minimum half-a-dozen NuGet dependencies just to make it happen. It’s a terrible, terrible mess.)

It seems like they want to consolidate all those APIs with Project Reunion

https://github.com/microsoft/ProjectReunion

So I'm hoping this improved things in the future.

lol, I forgot to mention: this is with Project Reunion. WinUI 3, CsWinRt, etc.

There is an API exposed in Windns.h but it doesn't work very well. It's awkward to use and doesn't pick up on services being added and removed. See `DnsService*`, etc in https://docs.microsoft.com/en-us/windows/win32/api/windns/.

I believe that's deprecated. The right thing to do - though very well hidden - is to use device enumeration:

https://docs.microsoft.com/en-us/windows/uwp/devices-sensors...

This uses mDNS under the hood and works pretty well now. The basics is that you create a device watcher and set it up to look for devices of a specific kind. In this case, you're looking for network-based devices with a specific service type.

It's however somewhat of a pain to get running as there's a lot of details you need to know / figure out before you can get running.

Have you shipped anything using that API? I'm just a bit weary of wasting time on another half-baked solution.

And are you sure the Windns.h API is deprecated? I could have sworn it only showed up last year.

I'm in the process of doing so. We had some issues with it initially but it seemed that it got better since a couple of updates ago. I vastly prefer it to having to ship mdnsresponder alongside my application though.

I'm basing my "deprecated" comment on this: https://docs.microsoft.com/en-us/uwp/api/Windows.Networking....

However that looks to be different from the windns.h stuff. To be honest, I wasn't aware of windns.h and just assumed it was the above link you were talking about. It's probably worth taking a look at :)

> I vastly prefer it to having to ship mdnsresponder alongside my application though.

That's what I'm seeking to avoid too. I'll have to take a closer look at the device enumeration API next time I circle around to the Windows port. Thanks for sharing your experience with it.

I'm the opposite. I strongly dislike these services as I feel they are not needed in many situations and open up the vulnerability potential, especially if your system is ever on a network not controlled by you (laptop at cafe, etc). I turn them all off/disable/uninstall them.

If you're on an untrusted network, run a firewall. An open network port isn't much safer just because you're not announcing it. People looking to attack your local web service at Starbucks probably know how to portscan.

The point is that instead of an open port for a service you close all the ports you dont need open, and then firewall what you do need. I'm saying stuff like avahi isn't needed in my case so I turn it off and of course thats not the only measure so I run a firewall amongst other things...

Reply on news.ycombinator.com