June 27, 2022

LSDP (Lenbrook Service Discovery Protocol) in Rust

When I moved to the US, one of the things I didn’t bring with me was my old amplifier for my speakers, since the one in Sweden only ran on 220/50Hz + wasn’t that great anyway. Bought a NAD C388 and it’s probably the worst piece of technology I own. Not only did the premise of the amplifier fall short (upgradeable modules to keep up with streaming) as they just redid the upgradeable system with the next generation anyway, it’s also been a nightmare in bad software design from NAD in my opinion.

So how would I salvage this? There are tons of open source solutions to do everything from digital room correction (Camilla DSP with FIR & IIR filters) to media servers that runs on a Raspberry Pi to play FLAC. Regardless of how we source the content to the amplifier, the challenge still remains to synchronize these devices which meant exploring controlling the amplifier using it’s API.

The amplifier does advertise itself over mDNS (Bonjour/Zeroconf) but the mDNS implementation seems shaky. After implementing the BluOS API in Rust I found myself struggle with the long time it takes between the mDNS announcements that the amplifier does (for some odd reason). Turns out that there is a second, non-standard discovery protocol that the manufacturer uses.

You’ve probably never heard about this protocol. Neither had I before implementing it. Lenbrook Group is the manufacturer behind brands like Bluesound, NAD etc. and have in their infinte wisdom decided that instead of leveraging the multitude of avaliable service discovery protocols out there, they would write their own.

Now why would a manufacturer forego using established standards like mDNS or SSDP? Lenbrook claims it’s because their customers lack the ability to configure their networks. Maybe if their customer didn’t buy audiophile” garbage routers this would be less of a problem but here we are.

The protocol is basically a worse version of mDNS over UDP Broadcast instead of UDP Multicast. In an effort to get some more experience with parsing binary protocols in Rust I wrote a library, mostly to explore Nom. Hence if you ever need to discover a Lenbrook device (NAD amplifier for example) you can use my Rust library on github.

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