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

* 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
2026-07-25 17:25:21 +00:00 · 2026-06-08 19:00:03 -05:00
parent 054887bad8
commit b079ae8742
3 changed files with 108 additions and 19 deletions
@@ -0,0 +1,86 @@
+package com.bitchat.android.sync
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import java.util.Random
+
+class GCSFilterTest {
+
+    @Test
+    fun testGCSFilterBasic() {
+        val random = Random(42)
+        val ids = List(20) {
+            val bytes = ByteArray(16)
+            random.nextBytes(bytes)
+            bytes
+        }
+
+        // Build filter with plenty of bytes (no trimming)
+        val params = GCSFilter.buildFilter(ids, maxBytes = 400, targetFpr = 0.01)
+        val sorted = GCSFilter.decodeToSortedSet(params.p, params.m, params.data)
+
+        for (id in ids) {
+            val v = GCSFilter.h64(id) % params.m
+            val nonZeroV = if (v == 0L) 1L else v
+            assertTrue("Filter should contain all encoded IDs", GCSFilter.contains(sorted, nonZeroV))
+        }
+    }
+
+    @Test
+    fun testGCSFilterWithTrimming() {
+        val random = Random(42)
+        // 50 IDs
+        val ids = List(50) {
+            val bytes = ByteArray(16)
+            random.nextBytes(bytes)
+            bytes
+        }
+
+        // Force trimming by setting maxBytes to a very small value (e.g., 20 bytes)
+        val maxBytes = 20
+        val params = GCSFilter.buildFilter(ids, maxBytes = maxBytes, targetFpr = 0.01)
+        
+        // Ensure some trimming actually happened
+        assertTrue("Params data size should be <= maxBytes", params.data.size <= maxBytes)
+        
+        val sorted = GCSFilter.decodeToSortedSet(params.p, params.m, params.data)
+
+        // Let's verify that the first trimmedN elements in ids are all matched
+        val trimmedN = (params.m ushr params.p).toInt()
+        assertTrue("At least some elements should have been encoded", trimmedN > 0)
+        
+        val retainedIds = ids.take(trimmedN)
+        for (id in retainedIds) {
+            val v = GCSFilter.h64(id) % params.m
+            val nonZeroV = if (v == 0L) 1L else v
+            assertTrue("Retained ID should be found in filter", GCSFilter.contains(sorted, nonZeroV))
+        }
+    }
+
+    @Test
+    fun testGCSFilterHandlesCollisionsAndZeroBucket() {
+        val random = Random(42)
+        // Generate a large number of IDs to guarantee collisions (mapping to the same bucket) and some zero-bucket mapping
+        val ids = List(200) {
+            val bytes = ByteArray(16)
+            random.nextBytes(bytes)
+            bytes
+        }
+
+        // Build GCS filter - this should complete successfully without throwing repeat count exceptions or negative-count crashes
+        val params = GCSFilter.buildFilter(ids, maxBytes = 100, targetFpr = 0.05)
+        val sorted = GCSFilter.decodeToSortedSet(params.p, params.m, params.data)
+
+        // Verify elements are successfully stored and found (including those mapping to 0)
+        var foundCount = 0
+        for (id in ids) {
+            val v = GCSFilter.h64(id) % params.m
+            val nonZeroV = if (v == 0L) 1L else v
+            if (GCSFilter.contains(sorted, nonZeroV)) {
+                foundCount++
+            }
+        }
+        assertTrue("Should successfully decode and find elements after deduplication", foundCount > 0)
+    }
+}