[#2193] Add Android voting JNI round lifecycle by greg0x · Pull Request #1938 · zcash/zcash-android-wallet-sdk

greg0x · 2026-05-08T17:38:48Z

Part of zodl-inc/zodl-android#2193.
Slice of #1924 (umbrella draft PR being split into reviewable pieces).
Depends on #1934 (first slice — zcash_voting dependency foundation).
Resolves MOB-1109

Why

Second slice of the Android shielded-voting integration. #1934 wires the zcash_voting crate into backend-lib; this PR adds the voting DB handle and round lifecycle so the round-keyed surface (init / state / list / get-votes / clear / delete-skipped) compiles end-to-end from Rust through JNI to Kotlin.

Foundation for the Coinholder Polling flow tracked in zodl-inc/zodl-android#2193 — no user-visible behavior on its own.

What's in

Rust / JNI (backend-lib/src/main/rust/voting/):

db.rs — open/close native handle, setWalletId
rounds.rs — initRound, getRoundState, listRoundsJson, getVotesJson, clearRound, deleteSkippedBundles
share_tracking.rs — existing computeShareNullifier, lifted out of the monolithic module
helpers.rs — shared JNI helpers: fixed-width byte validation (PROTOCOL_FIELD_BYTES = 32), jint/jlong widening, RoundState → FfiRoundState construction
json.rs — round summary / vote record serialization, RoundPhase ↔ u32 mapping
voting.rs — reduced to module roots + shared imports

Kotlin (sdk-lib/.../internal/):

jni/VotingRustBackend.kt — external declarations for the new surface
TypesafeVotingBackend.kt + impl — suspend wrappers, IO dispatcher, error checks, JSON → VoteRecord parsing
model/voting/FfiVotingModels.kt — FfiRoundState, FfiRoundPhase

Not included

hotkey generation
bundle setup/count
proving cache warmup
delegation proving/submission
vote commitment or share payloads
recovery/share tracking
public Synchronizer voting API

Review focus

Primary review track: core-dev. Please look at:

native handle lifecycle (Box::into_raw / Box::from_raw across openVotingDb/closeVotingDb, Arc<VotingDb> usage)
JNI boundary error semantics (panic-safe via catch_unwind, exception conversion)
byte-array validation (java_bytes_exact on 32-byte protocol fields)
RoundState / RoundSummary JSON and FFI mapping
Kotlin surface is intentionally internal and minimal — just enough to compile and exercise the JNI

Swift counterparts:

Validation

cargo check --manifest-path backend-lib/Cargo.toml --locked
cargo fmt --manifest-path backend-lib/Cargo.toml --check
./gradlew :backend-lib:compileReleaseKotlin :sdk-lib:compileReleaseKotlin
./gradlew ktlint detektAll
./gradlew checkProperties
git diff --check

Author

Self-review your own code in GitHub web interface
Add automated tests as appropriate
Update the manual tests as appropriate
Check the code coverage report for the automated tests
Update documentation as appropriate
Run the demo app and try the changes
Pull in the latest changes from the main branch and squash your commits before assigning a reviewer

Reviewer

Check the code with the Code Review Guidelines checklist
Perform an ad hoc review
Review the automated tests
Review the manual tests
Review the documentation as appropriate
Run the demo app and try the changes

noop-sk

PR added into code

The base branch was changed.

noop-sk · 2026-05-11T09:40:28Z

+    VOTE_READY(FFI_ROUND_PHASE_VOTE_READY);
+
+    companion object {
+        fun fromInt(value: Int) =


Forward compatibility risk

This throws if Rust adds a new RoundPhase variant before Kotlin is updated — a library update alone can crash the app. For an internal sdk-lib boundary it is defensible, but consider an UNKNOWN(-1) fallback or returning null until the phase set is stable.

This is an internal api contract between rust and kotlin. For this it's better to fail as soon as possible so the issue comes out during dev, failing silently.

The phase set can also be considered stable.

p.s.: I wish we could enjoy the comfort of UniFFI which solves this problem at generation time.

p.s.: I wish we could enjoy the comfort of UniFFI which solves this problem at generation time.

@noop-sk Is this something we should track as a future improvement?

noop-sk · 2026-05-11T10:37:12Z

+
+fn next_handle() -> anyhow::Result<jlong> {
+    NEXT_DB_HANDLE
+        .fetch_update(Ordering::Relaxed, Ordering::Relaxed, |id| {


@nuttycom — Ordering::Relaxed on both the success and failure orderings of fetch_update is correct for a monotone uniqueness counter on its own, since the registry Mutex provides the necessary acquire/release barriers around the actual map insert. Just flagging for a second pair of eyes given the subtle interaction between the two synchronization primitives.

Confirm, that the above is correct.

Addresses PR #1938 review comment #1.

Addresses PR #1938 review comment #2.

Addresses PR #1938 review comment #3.

Addresses PR #1938 review comment #5.

Addresses PR #1938 review comment #6.

Addresses PR #1938 review comment #7.

Addresses PR #1938 review comment #8.

nullcopy

Reviewed 3c8bd28

nullcopy · 2026-05-11T22:50:29Z

+    VOTE_READY(FFI_ROUND_PHASE_VOTE_READY);
+
+    companion object {
+        fun fromInt(value: Int) =


p.s.: I wish we could enjoy the comfort of UniFFI which solves this problem at generation time.

@noop-sk Is this something we should track as a future improvement?

nullcopy

utACK 450fe29

linear · 2026-06-01T10:07:14Z

MOB-1109

greg0x mentioned this pull request May 8, 2026

[#2193] Add Android voting JNI round lifecycle valargroup/zcash-android-wallet-sdk#5

Closed

13 tasks

p0mvn previously approved these changes May 8, 2026

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greg0x mentioned this pull request May 8, 2026

Only restore/save the Rust cache from jobs that compile Rust #1940

Merged

greg0x marked this pull request as ready for review May 9, 2026 05:36

greg0x mentioned this pull request May 9, 2026

[#1924] Add Android shielded-voting JNI foundation, round lifecycle, and delegation prep + signing valargroup/zcash-android-wallet-sdk#7

Closed

greg0x added 3 commits May 10, 2026 20:14

Split voting share nullifier JNI module

f81ebb0

Add voting DB round lifecycle JNI

af36d96

Add internal voting round lifecycle wrappers

f0106ae

greg0x force-pushed the greg/voting-rust-foundation branch from 75a95d7 to 350e2b1 Compare May 10, 2026 23:29

greg0x force-pushed the greg/voting-jni-db-rounds branch from 7171d4a to f0106ae Compare May 10, 2026 23:29

greg0x mentioned this pull request May 10, 2026

[#1924] Add Android voting delegation prep and signing #1942

Merged

13 tasks

noop-sk reviewed May 11, 2026

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Base automatically changed from greg/voting-rust-foundation to main May 11, 2026 09:33

noop-sk reviewed May 11, 2026

View reviewed changes

greg0x added 7 commits May 11, 2026 18:11

fix: Document FfiRoundState JNI constructor

662a871

Addresses PR #1938 review comment #1.

fix: Narrow missing round state handling

2098c32

Addresses PR #1938 review comment #2.

fix: Document round phase FFI constants

4447de6

Addresses PR #1938 review comment #3.

fix: Remove Keep from JSON round summary

7cd088b

Addresses PR #1938 review comment #5.

fix: Remove redundant deleted rows guard

fe73e0f

Addresses PR #1938 review comment #6.

fix: Move VoteRecord into voting models

e730711

Addresses PR #1938 review comment #7.

fix: Reuse voting Rust backend instance

3c8bd28

Addresses PR #1938 review comment #8.

nullcopy requested changes May 11, 2026

View reviewed changes

greg0x added 3 commits May 12, 2026 01:12

fix: Use typed JNI for voting round lists

c07f8e7

fix: Use zcash_voting round helper

dad02c3

fix: Rename voting JNI models

450fe29

greg0x force-pushed the greg/voting-jni-db-rounds branch from 30a2201 to 450fe29 Compare May 11, 2026 23:31

greg0x requested a review from nullcopy May 11, 2026 23:35

nullcopy approved these changes May 12, 2026

View reviewed changes

nullcopy merged commit 9e2fa1b into main May 12, 2026
15 checks passed

nullcopy deleted the greg/voting-jni-db-rounds branch May 12, 2026 00:23

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linear Bot commented Jun 1, 2026

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greg0x commented May 8, 2026 •

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