Minimal test project to investigate mDNS discovery behavior between desktop and iOS platforms using iroh.

Test mDNS-based peer discovery between desktop and iOS using iroh's swarm-discovery implementation.

Peers advertise themselves with user_data to enable definitive identification.

iroh-mdns-test/
├── mdns-peer/      # Shared implementation (CLI binary + iOS library)
├── MdnsTest/       # iOS app (Xcode project)
├── xtask/          # Build automation tasks (Rust-native)
└── Cargo.toml      # Workspace configuration

The mdns-peer crate provides both:

• A CLI binary that accepts a peer identifier as argument
• An iOS static library that can be embedded in Swift apps

• Rust toolchain with iOS targets:

  rustup target add aarch64-apple-ios aarch64-apple-ios-sim

• Xcode with iOS SDK

This project uses the xtask pattern for building - a Rust-native approach to build tasks.

cargo build --bin mdns-peer

Build for both iOS device and simulator in one command:

cargo xtask build-ios
# Or use the convenient alias:
cargo ios

Or both together for a fresh test

cargo build --bin mdns-peer && cargo ios

This will:

1. Build mdns-peer for aarch64-apple-ios (device)
2. Build mdns-peer for aarch64-apple-ios-sim (simulator)
3. Create the mdns_peer.xcframework directory structure
4. Copy the static libraries to the appropriate locations
5. Generate all required Info.plist files (XCFramework and per-architecture)

The XCFramework will be available at mdns-peer/mdns_peer.xcframework/ for use in Xcode.

About xtask: The xtask crate is a workspace member that provides build tasks as a Rust binary. This is the idiomatic Rust way to handle build automation - no bash scripts, no external tools like make, just pure Rust. See xtask/README.md for more details on the xtask pattern.

# Terminal 1 - Run as "alice"
cargo run --bin mdns-peer alice

# Terminal 2 - Run as "bob"
cargo run --bin mdns-peer bob

Each peer will advertise itself with its identifier and report discoveries.

Open MdnsTest/MdnsTest.xcodeproj in Xcode and run on simulator or device.

The iOS app calls bob_start() which internally uses identifier "bob".

Control logging verbosity using the RUST_LOG environment variable. The default configuration is:

RUST_LOG="mdns_peer=info,swarm_discovery=debug,iroh=info"

Verbose (see all mDNS activity):

RUST_LOG="mdns_peer=debug,swarm_discovery=debug,iroh=debug" cargo run --bin mdns-peer alice

Quiet (errors and warnings only):

RUST_LOG="mdns_peer=warn,swarm_discovery=warn,iroh=warn" cargo run --bin mdns-peer alice

Minimal (just peer discoveries):

RUST_LOG="mdns_peer=info,swarm_discovery=warn,iroh=warn" cargo run --bin mdns-peer alice

Everything (maximum verbosity):

RUST_LOG="trace" cargo run --bin mdns-peer alice

• swarm_discovery=debug - Shows mDNS queries, responses, and socket operations
• mdns_peer=info - Shows peer discoveries and routing table updates
• iroh=debug - Shows endpoint and network operations

Note: iOS logging is configured at compile time and always uses the default filter. To change iOS logging, modify mdns-peer/src/lib.rs and rebuild with cargo ios.

When peers discover each other, you'll see:

Peer discovered:
  Node ID: a8a2977385602aa4732868253fd0383678b37841d1bced7596456c60c768bab5
  User data: Some(UserData("alice"))
  Source: mdns
[[[ SUCCESS ]]]: Discovered peer 'alice'!

The user_data field provides definitive peer identification.

Symptom: iOS peer receives mDNS queries but cannot send responses:

WARN swarm_discovery::socket: error sending mDNS: No route to host (os error 65)

Result: One-way discovery only. iOS (Bob) successfully receives and discovers desktop (Alice), but fails to send mDNS responses (errno 65). Desktop (Alice) never discovers iOS peer, even with correct iOS entitlements and granted permissions

Potential Cause: The swarm-discovery crate does not properly configure multicast sockets for iOS. iOS requires:

• Explicit network interface binding
• SO_REUSEPORT socket option
• IP_MULTICAST_IF set correctly

Status: This is potentially a limitation of swarm-discovery on iOS, not a protocol compatibility issue.

• Simulator: Works both ways, nodes discover each other.
• Physical Device: One-way discovery only. iOS (Bob) successfully receives and discovers desktop (Alice), but fails to send mDNS responses (errno 65). Desktop (Alice) never discovers iOS peer, even with correct iOS entitlements and granted permissions
• Info.plist: Requires NSLocalNetworkUsageDescription and NSBonjourServices (already configured)

Same as iroh project (MIT/Apache-2.0)