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fix(sync): resolve hash alignment and early break bugs on GCS filter trimming (#708)

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* fix(sync): resolve hash alignment and early break bugs on GCS filter trimming

* fix(sync): filter out zero bucket and deduplicate buckets before encoding

* fix(sync): preserve zero-bucket mapping by clamping 0 to 1 during encoding and decoding
This commit is contained in:
a1denvalu3
2026-06-08 19:00:03 -05:00
committed by GitHub
parent 054887bad8
commit b079ae8742
3 changed files with 108 additions and 19 deletions
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app/src/main/java/com/bitchat/android/sync/GCSFilter.kt
+19 -11
View File
@@ -43,21 +43,29 @@ object GCSFilter {
targetFpr: Double
): Params {
val p = deriveP(targetFpr)
var nCap = estimateMaxElementsForSize(maxBytes, p)
val n = ids.size.coerceAtMost(nCap)
val selected = ids.take(n)
// Map to [0, M)
val m = (n.toLong() shl p)
val mapped = selected.map { id -> (h64(id) % m) }.sorted()
val nCap = estimateMaxElementsForSize(maxBytes, p)
var trimmedN = ids.size.coerceAtMost(nCap)
var finalM = (trimmedN.toLong() shl p).coerceAtLeast(1L)
var selected = ids.take(trimmedN)
var mapped = selected.map { id ->
val v = h64(id) % finalM
if (v == 0L) 1L else v
}.distinct().sorted()
var encoded = encode(mapped, p)
// If estimate was too optimistic, trim until it fits
var trimmedN = n
while (encoded.size > maxBytes && trimmedN > 0) {
trimmedN = (trimmedN * 9) / 10 // drop 10%
val mapped2 = mapped.take(trimmedN)
encoded = encode(mapped2, p)
finalM = (trimmedN.toLong() shl p).coerceAtLeast(1L)
selected = ids.take(trimmedN)
mapped = selected.map { id ->
val v = h64(id) % finalM
if (v == 0L) 1L else v
}.distinct().sorted()
encoded = encode(mapped, p)
}
val finalM = (trimmedN.toLong() shl p)
return Params(p = p, m = finalM, data = encoded)
}
@@ -96,7 +104,7 @@ object GCSFilter {
return false
}
private fun h64(id16: ByteArray): Long {
internal fun h64(id16: ByteArray): Long {
val md = MessageDigest.getInstance("SHA-256")
md.update(id16)
val d = md.digest()
app/src/main/java/com/bitchat/android/sync/GossipSyncManager.kt
+3 -8
View File
@@ -169,14 +169,9 @@ class GossipSyncManager(
// Decode GCS into sorted set for membership checks
val sorted = GCSFilter.decodeToSortedSet(request.p, request.m, request.data)
fun mightContain(id: ByteArray): Boolean {
val v = (GCSFilter.run {
// reuse hashing method from GCSFilter
val md = java.security.MessageDigest.getInstance("SHA-256");
md.update(id); val d = md.digest();
var x = 0L; for (i in 0 until 8) { x = (x shl 8) or (d[i].toLong() and 0xFF) }
(x and 0x7fff_ffff_ffff_ffffL) % request.m
})
return GCSFilter.contains(sorted, v)
val v = GCSFilter.h64(id) % request.m
val nonZeroV = if (v == 0L) 1L else v
return GCSFilter.contains(sorted, nonZeroV)
}
// 1) Announcements: send latest per peerID if remote doesn't have them