fix: incremental sync + unit tests for decide() logic

Sync change detection (3rd attempt — now correct):
- After UPLOAD: save null remote metadata (server mtime unknown until
  next listing); decide() treats null remoteModifiedAt as "not changed"
- After DOWNLOAD: read actual local mtime via accessor.lastModifiedMs()
  so the stored value matches what walkFiles() sees on next scan
- SKIP reconciliation: if known state has null timestamps and both sides
  exist, fill them in — stabilises state within 2 syncs after first transfer
- Extract syncDecide() as internal top-level function for testability

Unit tests (14 cases covering all key scenarios):
- First sync decisions (upload/download/conflict)
- Second sync after upload with null remote metadata → SKIP
- Second sync after download with recorded local mtime → SKIP
- Epoch-millis precision: same ms = SKIP, +1ms = change detected
- Regression: epoch-second stored value would have differed → now correct
- Delete behaviour (MIRROR vs KEEP)
- Direction filters (UPLOAD_ONLY, DOWNLOAD_ONLY)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
2026-05-23 00:13:00 +00:00
parent 5f45a344b7
commit a9322d3214
4 changed files with 235 additions and 78 deletions
@@ -8,6 +8,7 @@ import com.syncflow.data.db.SyncFileStateDao
import com.syncflow.data.db.SyncPairDao
import com.syncflow.data.db.entities.SyncConflictEntity
import com.syncflow.data.db.entities.SyncEventEntity
import com.syncflow.data.db.entities.SyncFileStateEntity
import com.syncflow.data.providers.CloudProvider
import com.syncflow.domain.model.ConflictStrategy
import com.syncflow.domain.model.DeleteBehavior
@@ -76,7 +77,7 @@ class SyncEngine @Inject constructor(
val uploaded: Int = 0, val downloaded: Int = 0, val deleted: Int = 0,
val skipped: Int = 0, val failed: Int = 0, val conflicts: Int = 0,
val bytesTransferred: Long = 0L,
val newState: com.syncflow.data.db.entities.SyncFileStateEntity? = null,
val newState: SyncFileStateEntity? = null,
)
val outcomes: List<FileOutcome> = coroutineScope {
@@ -86,7 +87,7 @@ class SyncEngine @Inject constructor(
val local = localFiles[rel]
val remote = remoteFiles[rel]
val known = knownStates[rel]
val decision = decide(pair.syncDirection, pair.conflictStrategy, pair.deleteBehavior, local, remote, known)
val decision = syncDecide(pair.syncDirection, pair.conflictStrategy, pair.deleteBehavior, local, remote, known)
when (decision) {
SyncDecision.UPLOAD -> {
@@ -101,7 +102,10 @@ class SyncEngine @Inject constructor(
return@withPermit FileOutcome(failed = 1)
}
logEvent(pair.id, SyncEventType.FILE_UPLOADED, rel, null, bytes)
FileOutcome(uploaded = 1, bytesTransferred = bytes, newState = buildState(pair.id, rel, local!!, remote))
// Remote metadata is unknown until the next listing; save null so
// decide() treats it as "not changed" and reconciles on next SKIP.
FileOutcome(uploaded = 1, bytesTransferred = bytes,
newState = buildState(pair.id, rel, local!!, remoteAfterTransfer = null))
}
SyncDecision.DOWNLOAD -> {
val bytes = runCatching {
@@ -114,8 +118,14 @@ class SyncEngine @Inject constructor(
logEvent(pair.id, SyncEventType.FILE_SKIPPED, rel, e.message, 0)
return@withPermit FileOutcome(failed = 1)
}
// Read the actual local mtime written by the OS/SAF after download.
val localMtime = runCatching { accessor.lastModifiedMs(rel) }
.getOrDefault(System.currentTimeMillis()).takeIf { it > 0L }
?: System.currentTimeMillis()
logEvent(pair.id, SyncEventType.FILE_DOWNLOADED, rel, null, bytes)
FileOutcome(downloaded = 1, bytesTransferred = bytes, newState = buildState(pair.id, rel, null, remote))
FileOutcome(downloaded = 1, bytesTransferred = bytes,
newState = buildState(pair.id, rel,
LocalFileInfo(rel, remote!!.sizeBytes, localMtime), remoteAfterTransfer = remote))
}
SyncDecision.DELETE_LOCAL -> {
accessor.delete(rel)
@@ -143,7 +153,19 @@ class SyncEngine @Inject constructor(
logEvent(pair.id, SyncEventType.CONFLICT_DETECTED, rel, null, 0)
FileOutcome(conflicts = 1)
}
SyncDecision.SKIP -> FileOutcome(skipped = 1)
SyncDecision.SKIP -> {
// Reconcile: if the known state is missing remote or local metadata
// (saved right after an upload before we had the server's response),
// fill it in now that we have the full listing.
val needsReconcile = known != null &&
(known.remoteModifiedAt == null || known.localModifiedAt == null) &&
local != null && remote != null
if (needsReconcile) {
FileOutcome(skipped = 1, newState = buildState(pair.id, rel, local, remoteAfterTransfer = remote))
} else {
FileOutcome(skipped = 1)
}
}
}
}
}
@@ -162,86 +184,20 @@ class SyncEngine @Inject constructor(
)
}
private fun decide(
direction: SyncDirection,
conflictStrategy: ConflictStrategy,
deleteBehavior: DeleteBehavior,
local: LocalFileInfo?,
remote: RemoteFile?,
known: com.syncflow.data.db.entities.SyncFileStateEntity?,
): SyncDecision {
val localExists = local != null
val remoteExists = remote != null
val localChanged = known == null || (localExists && local!!.lastModifiedMs != known.localModifiedAt?.toEpochMilli())
val remoteChanged = known == null || (remoteExists && (remote!!.etag != known.remoteEtag || remote.modifiedAt != known.remoteModifiedAt))
return when {
!localExists && !remoteExists -> SyncDecision.SKIP
localExists && !remoteExists -> when {
known == null -> when (direction) {
SyncDirection.UPLOAD_ONLY, SyncDirection.TWO_WAY -> SyncDecision.UPLOAD
else -> SyncDecision.SKIP
}
else -> when {
deleteBehavior == DeleteBehavior.KEEP -> SyncDecision.SKIP
direction == SyncDirection.DOWNLOAD_ONLY || direction == SyncDirection.TWO_WAY -> SyncDecision.DELETE_LOCAL
else -> SyncDecision.SKIP
}
}
!localExists && remoteExists -> when {
known == null -> when (direction) {
SyncDirection.DOWNLOAD_ONLY, SyncDirection.TWO_WAY -> SyncDecision.DOWNLOAD
else -> SyncDecision.SKIP
}
else -> when {
deleteBehavior == DeleteBehavior.KEEP -> SyncDecision.SKIP
direction == SyncDirection.UPLOAD_ONLY || direction == SyncDirection.TWO_WAY -> SyncDecision.DELETE_REMOTE
else -> SyncDecision.SKIP
}
}
localChanged && remoteChanged -> when (direction) {
SyncDirection.UPLOAD_ONLY -> SyncDecision.UPLOAD
SyncDirection.DOWNLOAD_ONLY -> SyncDecision.DOWNLOAD
SyncDirection.TWO_WAY -> when (conflictStrategy) {
ConflictStrategy.KEEP_LOCAL -> SyncDecision.UPLOAD
ConflictStrategy.KEEP_REMOTE -> SyncDecision.DOWNLOAD
ConflictStrategy.KEEP_NEWEST -> if ((local?.lastModifiedMs ?: 0L) >= (remote?.modifiedAt?.toEpochMilli() ?: 0L)) SyncDecision.UPLOAD else SyncDecision.DOWNLOAD
ConflictStrategy.KEEP_LARGEST -> if ((local?.sizeBytes ?: 0L) >= (remote?.sizeBytes ?: 0L)) SyncDecision.UPLOAD else SyncDecision.DOWNLOAD
ConflictStrategy.KEEP_BOTH -> SyncDecision.CONFLICT
ConflictStrategy.ASK -> SyncDecision.CONFLICT
}
}
localChanged -> when (direction) {
SyncDirection.UPLOAD_ONLY, SyncDirection.TWO_WAY -> SyncDecision.UPLOAD
else -> SyncDecision.SKIP
}
remoteChanged -> when (direction) {
SyncDirection.DOWNLOAD_ONLY, SyncDirection.TWO_WAY -> SyncDecision.DOWNLOAD
else -> SyncDecision.SKIP
}
else -> SyncDecision.SKIP
}
}
private fun buildState(
pairId: Long,
rel: String,
local: LocalFileInfo?,
remote: RemoteFile?,
) = com.syncflow.data.db.entities.SyncFileStateEntity(
remoteAfterTransfer: RemoteFile?,
) = SyncFileStateEntity(
syncPairId = pairId,
relativePath = rel,
localModifiedAt = local?.lastModifiedMs?.let { Instant.ofEpochMilli(it) },
localSizeBytes = local?.sizeBytes ?: 0L,
localHash = null,
remoteModifiedAt = remote?.modifiedAt,
remoteSizeBytes = remote?.sizeBytes ?: 0L,
remoteEtag = remote?.etag,
remoteModifiedAt = remoteAfterTransfer?.modifiedAt,
remoteSizeBytes = remoteAfterTransfer?.sizeBytes ?: 0L,
remoteEtag = remoteAfterTransfer?.etag,
lastSyncedAt = Instant.now(),
syncedHash = null,
)
@@ -251,6 +207,79 @@ class SyncEngine @Inject constructor(
}
}
// Top-level so unit tests can call it directly without instantiating SyncEngine.
internal fun syncDecide(
direction: SyncDirection,
conflictStrategy: ConflictStrategy,
deleteBehavior: DeleteBehavior,
local: LocalFileInfo?,
remote: RemoteFile?,
known: SyncFileStateEntity?,
): SyncDecision {
val localExists = local != null
val remoteExists = remote != null
// Treat null known timestamps as "not yet recorded" — don't treat as changed.
// The SKIP reconciliation pass will fill them in on the next sync.
val localChanged = known == null ||
(localExists && known.localModifiedAt != null &&
local!!.lastModifiedMs != known.localModifiedAt.toEpochMilli())
val remoteChanged = known == null ||
(remoteExists && known.remoteModifiedAt != null &&
(remote!!.etag != known.remoteEtag || remote.modifiedAt != known.remoteModifiedAt))
return when {
!localExists && !remoteExists -> SyncDecision.SKIP
localExists && !remoteExists -> when {
known == null -> when (direction) {
SyncDirection.UPLOAD_ONLY, SyncDirection.TWO_WAY -> SyncDecision.UPLOAD
else -> SyncDecision.SKIP
}
else -> when {
deleteBehavior == DeleteBehavior.KEEP -> SyncDecision.SKIP
direction == SyncDirection.DOWNLOAD_ONLY || direction == SyncDirection.TWO_WAY -> SyncDecision.DELETE_LOCAL
else -> SyncDecision.SKIP
}
}
!localExists && remoteExists -> when {
known == null -> when (direction) {
SyncDirection.DOWNLOAD_ONLY, SyncDirection.TWO_WAY -> SyncDecision.DOWNLOAD
else -> SyncDecision.SKIP
}
else -> when {
deleteBehavior == DeleteBehavior.KEEP -> SyncDecision.SKIP
direction == SyncDirection.UPLOAD_ONLY || direction == SyncDirection.TWO_WAY -> SyncDecision.DELETE_REMOTE
else -> SyncDecision.SKIP
}
}
localChanged && remoteChanged -> when (direction) {
SyncDirection.UPLOAD_ONLY -> SyncDecision.UPLOAD
SyncDirection.DOWNLOAD_ONLY -> SyncDecision.DOWNLOAD
SyncDirection.TWO_WAY -> when (conflictStrategy) {
ConflictStrategy.KEEP_LOCAL -> SyncDecision.UPLOAD
ConflictStrategy.KEEP_REMOTE -> SyncDecision.DOWNLOAD
ConflictStrategy.KEEP_NEWEST -> if ((local?.lastModifiedMs ?: 0L) >= (remote?.modifiedAt?.toEpochMilli() ?: 0L)) SyncDecision.UPLOAD else SyncDecision.DOWNLOAD
ConflictStrategy.KEEP_LARGEST -> if ((local?.sizeBytes ?: 0L) >= (remote?.sizeBytes ?: 0L)) SyncDecision.UPLOAD else SyncDecision.DOWNLOAD
ConflictStrategy.KEEP_BOTH -> SyncDecision.CONFLICT
ConflictStrategy.ASK -> SyncDecision.CONFLICT
}
}
localChanged -> when (direction) {
SyncDirection.UPLOAD_ONLY, SyncDirection.TWO_WAY -> SyncDecision.UPLOAD
else -> SyncDecision.SKIP
}
remoteChanged -> when (direction) {
SyncDirection.DOWNLOAD_ONLY, SyncDirection.TWO_WAY -> SyncDecision.DOWNLOAD
else -> SyncDecision.SKIP
}
else -> SyncDecision.SKIP
}
}
enum class SyncDecision { UPLOAD, DOWNLOAD, DELETE_LOCAL, DELETE_REMOTE, CONFLICT, SKIP }
data class SyncResult(