Feat/lan server discovery

[Toys0125]

Summary

• Adds support for local clients, and server to announce in mDNS, which is UDP multicast their listening address.
• Auto discovery for LAN multicast of Basis Servers which get added to the top of the server browser.
• Asks for password when needed.

Required checks

All boxes below must be ticked before this PR can merge. If a check is genuinely N/A, tick it anyway and explain under Notes.

• Tested — I built and ran this locally. The change works in the editor and (where relevant) in a built player.
• Transform access is combined and limited — In hot paths, transform reads/writes go through TransformAccessArray or are otherwise batched. I have not added per-frame transform.position / transform.rotation / transform.localPosition calls inside loops. Whenever I need both position and rotation, I use the combined APIs — SetPositionAndRotation / SetLocalPositionAndRotation for writes, GetPositionAndRotation / GetLocalPositionAndRotation for reads — instead of two separate property accesses; the combined call does one local-to-world matrix traversal instead of two.
• Addressables used for asset/memory loading — Any new asset loads go through Addressables. No new Resources.Load, no direct asset references that pull large content into memory on scene load.
• No new GetComponent / AddComponent where avoidable — Where unavoidable, the result is cached on a field, and any GetComponent<T> is replaced with TryGetComponent<T>(out var x) — bare GetComponent will be denied. TryGetComponent is the modern API (Unity 2019.2+) and skips the Editor-only GC allocation GetComponent causes when a component is missing: Unity wraps the null return in a managed "fake null" object so its overloaded == operator can still detect destroyed C++ objects, and constructing that wrapper allocates; TryGetComponent returns a bool plus out parameter and never builds the wrapper. None of these calls run inside Update, LateUpdate, FixedUpdate, jobs, or other per-frame code paths.
• Per-frame work is scheduled through BasisEventDriver — Any new per-frame work hooks into BasisEventDriver rather than adding standalone Update / LateUpdate / FixedUpdate callbacks on a MonoBehaviour.
• Anything added to BasisEventDriver is bulletproof, or guarded by try/catch — BasisEventDriver runs the single per-frame tick that drives the whole framework (network apply, local player sim, blendshapes, JigglePhysics, nameplates, and more) as one sequential chain. An unhandled exception anywhere in that chain aborts the rest of the tick, so every step after the throwing one is silently skipped for that frame. New work added to the driver must either be guaranteed not to throw, or be wrapped in a try/catch that contains the failure and surfaces it through BasisDebug — logged once / rate-limited, never every frame (see the existing HVRBasisBuiltInAddresses.Simulate() guard for the pattern). Expect this to be scrutinized closely in review.
• Considered jobification — I asked whether this work can be moved to a Unity Job (Burst-compiled where possible). If it can, it is. If it cannot, the reason is in Notes.
• No needless { get; set; } properties or access lockdowns — Public fields are fine; Basis is meant to be read and modified freely, so don't wall things off private/internal without a real reason. Don't wrap a field in { get; set; } when the accessors do nothing — property accessors have a real performance cost vs direct field access, and the lead maintainer prefers plain fields (or a method / setter-only property when only the setter needs logic) over a noop-getter pair. For .Instance singletons, callers reassigning Type.Instance is allowed; if that would break your code, log a warning or throw — don't block the assignment. Locking down access is not your call.
• Camera access goes through BasisLocalCameraDriver — Code that needs the local camera (transform, projection, rig data, etc.) pulls it from BasisLocalCameraDriver rather than looking one up itself. Don't roll a separate camera discovery path.
• Logging uses BasisDebug — All new logging calls go through BasisDebug.Log / BasisDebug.LogWarning / BasisDebug.LogError (with an appropriate LogTag) instead of UnityEngine.Debug.Log / Debug.LogWarning / Debug.LogError. BasisDebug routes through Basis's tagged, color-coded logger and respects the project-wide LoggingDisabled toggle so logging can be killed at runtime; bare Debug.Log calls bypass that and will be denied.
• No scene-wide discovery for dependencies — New code is architected so it does not need FindObjectOfType / FindObjectsOfType / GameObject.Find / FindGameObjectsWithTag to locate what it depends on. References are wired in — registered through an existing manager/driver, injected at init, or passed in by the caller — rather than discovered by scanning the scene at runtime. If a scene scan is genuinely unavoidable, justify it under Notes.
• No allocations in hot paths — Per-frame code (Update / LateUpdate / FixedUpdate, simulation loops, jobs, anything called once per frame or more) does not allocate. No new on reference types, no LINQ, no string concatenation/interpolation, no boxing, no foreach over interface-typed collections. Allocate once at init and reuse the buffer.
• No debugging in hot paths — No log calls of any kind on per-frame paths, including BasisDebug. Hot-path logging floods the console and incurs cost on every frame regardless of whether the message is filtered out downstream. If a hot-path log is needed while iterating, gate it behind #if UNITY_EDITOR and remove (or leave gated) before merge.
• Hot-path collection access is optimized — Cache .Count (lists) / .Length (arrays) into a local int before the loop instead of re-reading the property each iteration. Prefer T[] (with a separate length int when the array is over-sized) over List<T> where the data is hot — Unity's mono BCL doesn't expose CollectionsMarshal.AsSpan(List<T>), so a list can't be fed into Span<T> / unsafe paths cleanly. Where the perf justifies it, drop into Span<T> / ref locals / Unsafe.As / unsafe pointer code to skip bounds checks and copies, and call out the invariants you're relying on under Notes so reviewers can sanity-check them.

Testing details

Tick the platforms you actually tested on. Leave the rest unticked — these are informational and do not block merge.

• Windows
• Linux
• Android
• iOS
• macOS

Input / control mode coverage:

• Tested in VR (note headset under Notes)
• Tested in desktop / non-VR mode
• Tested with phone controls (mobile touch input)
• N/A — change does not touch player/XR/input code

Where applicable, confirm these flows still work after your changes:

• Hot-switching (desktop ↔ VR mode swap at runtime)
• Avatar swapping
• Server swapping (joining / leaving / changing servers)
• N/A — change does not touch any of the above

Notes

[yewnyx]

I think this needs a concrete proposal and testing on all platforms for a couple of reasons

• There is significant divergence in system policy on allowed advertisement. Android has certain multicast rules for advertisements, iOS has others
• This is adjacent to deep linking work in that advertisement is a frontend concern to different clients, which should either advertise differently, or advertise in some way that accommodates separate clients and versions - or even incorporate deep linking to advertise the connect URL (possibly even with or without password included in the advertisement)

[yewnyx]

In particular I have used MeaMod for advertisements on Windows in the past and discovered that Android did not successfully send nor receive advertisements. That was a while ago and on a different project, but care must be taken to test on all platforms and with multiple different platforms interacting

[Toys0125]

@yewnyx you 100% right, Its weird that Windows will see the Android broadcast, but couldn't connect to the Android hosted server.

[cnlohr]

This whole thing feels like a very different shape than it should be, there's a ton of repeated logic here that also exists in other portions of Basis' existing server browser.

In my opinion, a much better structure would be:

• Have the server browser have the ability to have temporary server slots that are discovered.
• Basis sends messages to a multicast group with a special magic word.
• When Basis sees messages from the multicast group with that magic word, it adds them to the server list as a temporary item.
• The server browser will handle all the logic surrounding MOTD, server name, connection, etc.

[dooly123]

@Toys0125 mind giving @cnlohr post a read?

[Toys0125]

This whole thing feels like a very different shape than it should be, there's a ton of repeated logic here that also exists in other portions of Basis' existing server browser.

In my opinion, a much better structure would be:

• Have the server browser have the ability to have temporary server slots that are discovered.
• Basis sends messages to a multicast group with a special magic word.
• When Basis sees messages from the multicast group with that magic word, it adds them to the server list as a temporary item.
• The server browser will handle all the logic surrounding MOTD, server name, connection, etc.

I purposely tried to keep majority of the server discover temp logic in here as i don't believe that the additional bloat should be integrated into it if someone wants this package removed.
We already using mDNS as that has the least resistance on firewalls and routers. Using the Domain name as the "Magic Word".

[yewnyx]

@cnlohr non-mDNS multicast are a non-starter on mobile platforms; these are blocked on both Android and iOS, except in special cases, and when they are made available, they are throttled for battery life.

My feedback is, summarized:

• Server discovery should not be a universal-by-default negotiation with other clients
• Server discovery should not conflict with rfc2782-based service naming, and ideally use the same service naming
• Server discovery should be designed with the explicit expectation that the data payload may want to indicate not just server URLs, but desired client (most likely suggested with a URL scheme), as a multi-client universe is expected and discovery mechanisms for heterogeneous server forks is expected, but outside the scope of the core framework at least until the mechanisms for navigating the multi-client universe have been proven.
• Server discovery over WAN is an explicit non-goal for now, at least until all of the above have been implemented, if not longer, to avoid platform incentives.