zig-oura

Native Oura Ring BLE protocol and history sync, based on open_oura. The protocol, AES challenge, event decoding, and checkpoint state machine run in Zig. Native hosts use a C ABI; the optional TypeScript client uses the same compiled code through WASM.

Status

Experimental interoperability implementation for the shared Ring 3/4/5 protocol. Captured Ring 5 records, synthetic failure cases, the C ABI, and the Swift binding are tested. Physical pairing and firmware compatibility have not yet been validated with this implementation. Tests are not a hardware certification.

Implemented:

• Allocation-free native framing, AES-128 nonce authentication, firmware/battery parsing, command builders, and live heart-rate validation.
• Legacy history and split/coalesced Ring 5 extended envelopes, retaining every event body, including unknown event types.
• HR/5-minute RMSSD, SpO2, temperature, quality-checked IBI, sleep-stage and MET decoders; standard RMSSD over supplied inter-beat intervals.
• Incremental native sessions with caller-owned memory, deadlines, complete batch validation, explicit durable acceptance, and checkpoint commits.
• Ring 5 stream registration, capability reads, bounded native GATT operations, explicit legacy negotiation, small-tail drain handling, and live-mode teardown.
• Stable C ABI, Swift binding, and an independent WASM instance per JS client.

A ring already configured with an Oura app needs its existing 16-byte pairing key, not its account password or cloud OAuth token. This library does not extract an existing key, replace a configured pairing, or reset the ring. The application owns consent, Bluetooth permissions, secure key storage, and the native GATT connection.

Oura's proprietary models and firmware are not included. This package does not claim to reproduce official Sleep/Readiness/Activity scores. Raw ring readings and locally derived values must retain their provenance; an application can keep Oura's cloud integration for data unavailable directly from the ring.

Build and verify

Pinned tools are in deps.yaml: Bun 1.4.4 and Zig 0.17.0-dev.1441+d5181a9c9. No external runtime dependencies are required by the Zig library. better-dx supplies the JS development tools.

pantry install
bun install --frozen-lockfile
zig build
zig build test
bun run build
bun run typecheck
bun test ./test
bun run lint
bun run bench
# macOS, using the native library rather than WASM:
bun run test:swift

zig build installs liboura.a, oura.h, and the Swift module map. zig build wasm builds the portable module. bun run build embeds that module and builds the TypeScript entry point. test/ring5-capture.json records the immutable reference revision and independent expected records; the tests replay the capture at every possible envelope split boundary.

The benchmark measures native C-ABI decoding of a small HRV event into four readings. It excludes Bluetooth, storage and application callbacks. It is a local throughput measurement, not a claim about radio sync speed.

Native Zig

Add an immutable release source archive as a Zig dependency and import its oura module:

const oura = ;
var scratch: [65535]u8 = undefined;
var session = oura.session.Session.init(&scratch);
defer session.close();
const first = try session.begin(pairing_key, monotonic_milliseconds);
// Send first.write through the Oura GATT write characteristic.
// Feed every complete packet from protocol.Iterator to session.receive().

GATT identifiers are protocol.service_uuid, write_uuid, and notify_uuid. Subscribe to the Oura service's notification/indication characteristics before writing; newer rings can expose additional notifying characteristics.

During history sync, persist every .event, then call acceptEvent() and next() until .none. At .batch, durably persist its candidate checkpoint with the accepted records before commitBatch(). Never advance a checkpoint on a timeout, partial envelope, count mismatch or failed storage operation. The client sends no history deletion, reset, firmware update, or ack-fetch.

Cursors and event timestamps are ring-relative deciseconds, not Unix dates. Extended events also retain their original ring milliseconds. Wall-clock anchors and ring/reset identity must be retained by storage; do not attach raw history to the current date or reuse another ring's cursor.

C and Swift

include/oura.h documents output kinds and error codes. Allocate the reported context size/alignment and independent scratch memory. A context has one owner; independent contexts can run on different threads. Output pointers are borrowed until the next call. test/abi.c is a compiled C usage example.

bindings/swift/OuraSession.swift owns those buffers and wraps the same native C ABI. Import ZigOura using include/module.modulemap, link liboura.a, and own the session on a serial actor or queue. Its receive callback must finish persisting each event before returning. test/SwiftSmoke.swift exercises native authentication, event decoding and checkpointing without JavaScript or WASM.

TypeScript

The portable npm-format package is @zig-utils/oura. GitHub releases include its package tarball; the native source is published through Pantry.

import { connectOuraBluetooth } from '@zig-utils/oura'

// An explicitly selected device, with an ordered native GATT stream.
const client = await connectOuraBluetooth(bluetooth, selectedDeviceId)
try {
  await client.open(existingPairingKey)
  await client.sync({
    cursor: await store.cursorFor(ringId, resetGeneration),
    onEvent: async event => { await store.acceptIdempotently(event) },
    onBatch: async batch => { await store.commitCheckpoint(batch.nextCursor) },
  })
}
finally { await client.close() }

For other transports, construct new OuraBleClient(transport, protocol). The host supplies write(bytes), read(timeoutMs), and close(). Queue notifications before any write, preserve their order, reject overflow and disconnect, and cancel outstanding operations on close. The client also bounds I/O itself and preserves the original failure if teardown fails. Radio reconnect policy belongs to the application and resumes from its last durable checkpoint.

connectOuraBluetooth adapts a native GATT bridge, validates every incoming byte, erases temporary write copies, and closes failed or cancelled connections. It never scans, authenticates, or installs a key implicitly. current can bind its operations to the signed-in account.

createOuraProtocol uses WASM. A host without WebAssembly must inject an OuraProtocol backed by the native C ABI; this package has no separate JS implementation of the wire protocol or cryptography.

To stream HR briefly, use client.heartRate(durationMs, onSample). It confirms restoration of automatic mode after a normal stop or callback failure; closing an active stream attempts restoration before disconnecting. Protocol logs must never include pairing keys or authentication payloads.

Initial setup of an unconfigured ring

An existing configured ring must use open(existingPairingKey). A missing key is not permission to overwrite the pairing. pair() proceeds only after the ring itself reports the unconfigured authentication result; a configured ring cannot enter the key-install state.

For an already unconfigured ring, generate a cryptographically random 16-byte key (crypto.getRandomValues on a supported host or OuraNativeSession.generatePairingKey() on Apple platforms), then:

await client.pair({
  key: generatedKey,
  confirmUnconfigured: true,
  persistKey: async key => { await keychain.storeFor(ringId, key) },
})

The callback must durably copy the key before resolving. Its temporary argument is erased afterward. The client installs the key only after storage succeeds, then performs a new nonce challenge to verify authentication. Retain the stored key if the radio disconnects during installation: the ring may already have accepted it. Resume with open() and the same stored key. Never generate a new key merely because a connection failed.

The Swift/C session exposes the same guarded install operation; the host must persist the key first. Treat write outputs with auxiliary == 1 as sensitive: never log or retain their payloads, and erase host copies after writing. A GATT transport must remain bound to one ring for the lifetime of a client; it must not silently reconnect to another device during setup or history sync.

Releases

Follow the zig-starter workflow: conventional commits, a clean source tree, Pantry-managed version/changelog/commit/tag, then the release workflow.

bun run release:preview
bun run release          # pantry release patch --yes
# Or release:minor / release:major

Review CHANGELOG.md and the release source. The tag workflow rebuilds and tests the package, uses stacksjs/action-releaser, and publishes the Zig source through Pantry using PANTRY_TOKEN. Versioning is shared by package.json and build.zig.zon; do not hand-edit one during a release.

Attribution

Protocol reference: Thomas Marchand's MIT-licensed Th0rgal/open_oura, revision e57c43ce5fe0cf9a646afa790bda3731be767507. See NOTICE.md for its license and provenance. This project is independent of Oura.