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midi-harbor/specs/013-windows-support/plan.md
James Coleman 488e42b9c8 First commit
2026-09-28 13:59:10 -05:00

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Implementation Plan: Windows support

Branch: 002-windows-support, this spec's original name | Date: 2026-09-26 | Spec: spec.md

Input: Feature specification from /specs/013-windows-support/spec.md

Summary

Give each of the four platform seams a Windows implementation, move the two pieces that were Unix-only outside the seams (the IPC transport and service installation) onto a Windows equivalent, and cross-compile from macOS with mingw-w64. The Windows test machine runs the cross-compiled test binaries; nothing is compiled on it.

Technical Context

Target: x86_64-pc-windows-gnu, linked by x86_64-w64-mingw32-gcc (Homebrew mingw-w64), configured in .cargo/config.toml.

New dependencies: windows 0.62, windows-core 0.62 and windows-collections 0.3, for the WinRT classes of Windows MIDI Services, whose bindings scripts/midi2-bindings generates from Microsoft's metadata with windows-bindgen 0.64; windows-sys 0.61 (already in the tree through tokio), for WinMM, the power manager, DNS-SD, events and loading DLLs; socket2 0.6 (already in the tree), for dual-stack sockets on every platform. zeroconf moves from the daemon to the platform crate and is not built on Windows, where it would need Apple's Bonjour SDK.

Test machine: Windows 11 Pro 25H2 (build 26200), with rtpMIDI 1.1.14 and so teVirtualMIDI 1.3.0.43, and the Windows MIDI Services SDK Runtime and Tools RC4 (1.0.17-rc.4.25) against the in-box service 10.0.26100.7705; no Bluetooth radio and no USB MIDI hardware.

Decisions

Area Windows implementation Why
Virtual ports Windows MIDI Services virtual devices, one function block and group per connector: through Windows.Devices.Midi2 when Windows registers it, otherwise through the App SDK runtime teVirtualMIDI may not be distributed without its author's clearance. Windows carries the API from its late-2026 update; the App SDK serves until then (R-093).
Service calls Each on a thread of its own, waited for 5 s, 30 s when opening a session; once one outlives its wait, virtual ports are refused until it returns The service before the late-2026 update never answers a device's disconnection (R-093).
Devices WinMM, input by callback into the ring, output by short and long messages Every other interface's ports appear in WinMM.
Device identity Interface path for hardware; name alone for application ports; this process's own ports by their connector names and by the service's group names teVirtualMIDI numbers the halves of a port separately and renumbers them (R-086); the service before the late-2026 update names ports after groups (R-093).
Hot-plug The lists compared once a second WinMM announces nothing without a window to post to.
IPC Named pipe, remote clients refused, random name recorded at the socket path Tokio has no AF_UNIX on Windows; the recorded name keeps a file permission as the gate (R-087).
Stopping A named event in the session namespace, set by service stop Windows has no SIGTERM; ending the task would skip releasing notes.
Service Task Scheduler logon task, interactive token, least privilege, normal priority, conhost --headless A Windows service runs in session 0 and needs an administrator.
Crash restart daemon --supervise, restarting after 2 s, doubling to 60 s while failures come quickly Task Scheduler does not restart a program that exits with an error (R-083).
Advertising The DNS Client service's DnsServiceRegister, looked up at run time The system responder answers other machines for as long as the registration lasts; dots become hyphens (R-084).
Sockets IPV6_V6ONLY cleared explicitly Windows defaults to IPv6-only (R-085).
Sleep and wake PowerRegisterSuspendResumeNotification, holding a suspend up to 1.9 s The polled watcher runs underneath, as on the other platforms.
Bluetooth Central through btleplug's WinRT backend; peripheral not built No radio was available to verify either role; the central code is shared with the other platforms.

Constitution Check

  • I. Resilience: crash restart by the supervisor; opens retried while the device list moves; a stalled Windows MIDI Service costs virtual ports and nothing else.
  • II. Daemon owns state: unchanged; the service is a logon task.
  • III. Real-time safety: the WinMM and Windows MIDI Services callbacks only translate and scan into the ring and, for WinMM, hand system-exclusive buffers back. They allocate, lock and log nothing. Buffers are allocated when an input opens.
  • IV. Parity: every seam has a Windows implementation except the BLE peripheral, declared in the Platform Support Matrix and reported unavailable (amendment 1.1.0).
  • V. Protocol correctness: unchanged code; a Windows daemon joined a session with Linux.
  • VI. Testable without hardware: device identity, port naming, UMP translation, message packing, service definitions and the supervisor's pacing are pure and tested on every platform.
  • VII. Observable: unchanged.
  • Unsafe code: confined to the platform crate, each block with a SAFETY comment.

Complexity Tracking

Deviation Why Simpler alternative rejected
BLE peripheral not built on Windows No Windows machine with a radio to verify it Enabling ble-peripheral-rust's WinRT backend unverified
A supervisor mode in the binary Task Scheduler does not restart a failed program (R-083) A task repeating every minute, which restarts after up to a minute and also restarts a daemon the user stopped

Project Structure

.cargo/config.toml                     the mingw-w64 linker for the Windows target
crates/platform/src/dll.rs             run-time DLL loading
crates/platform/src/responder/         advertising: zeroconf, or DNS-SD on Windows
crates/platform/src/stop.rs            the stop event
crates/platform/src/midi/windows.rs    the backend behind the MIDI seam
crates/platform/src/midi/winmm.rs      WinMM inputs and outputs
crates/platform/src/midi/wms/         Windows MIDI Services ports, in-box and App SDK
crates/platform/src/midi/ump.rs        Universal MIDI Packet translation, tested everywhere
crates/platform/src/midi/winmm_identity.rs  identity and message packing, tested everywhere
crates/platform/src/sysevents/windows.rs    suspend and resume
crates/platform/tests/windows_midi.rs  the Windows integration tests
crates/ipc/src/transport/windows.rs    the named pipe
crates/service/src/taskscheduler.rs    the logon task
crates/service/src/supervisor.rs       restarting after a crash
scripts/midi2-bindings/                generating the Windows MIDI Services bindings