fix: use a known hash seed for variant hashing, this fixes a bug in v…

…ariant distribution
Unleash · Oct 30, 2023 · 270cf42 · 270cf42
1 parent d60019b
commit 270cf42
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Showing 3 changed files with 7 additions and 5 deletions.
diff --git a/src/Stickiness/MurmurHashCalculator.php b/src/Stickiness/MurmurHashCalculator.php
@@ -6,8 +6,8 @@
 
 final class MurmurHashCalculator implements StickinessCalculator
 {
-    public function calculate(string $id, string $groupId, int $normalizer = 100): int
+    public function calculate(string $id, string $groupId, int $normalizer = 100, int $seed = 0): int
     {
-        return Murmur::hash3_int("{$groupId}:{$id}") % $normalizer + 1;
+        return Murmur::hash3_int("{$groupId}:{$id}", $seed) % $normalizer + 1;
     }
 }
diff --git a/src/Stickiness/StickinessCalculator.php b/src/Stickiness/StickinessCalculator.php
@@ -4,5 +4,5 @@
 
 interface StickinessCalculator
 {
-    public function calculate(string $id, string $groupId, int $normalizer = 100): int;
+    public function calculate(string $id, string $groupId, int $normalizer = 100, int $seed = 0): int;
 }
diff --git a/src/Variant/DefaultVariantHandler.php b/src/Variant/DefaultVariantHandler.php
@@ -11,6 +11,8 @@
 
 final class DefaultVariantHandler implements VariantHandler
 {
+    const VARIANT_HASH_SEED = 86028157;
+
     public function __construct(
         private readonly StickinessCalculator $stickinessCalculator,
     ) {
@@ -94,7 +96,7 @@ private function calculateStickiness(
         int $totalWeight
     ): int {
         $stickiness = $variants[0]->getStickiness();
-        if ($stickiness !== Stickiness::DEFAULT) {
+        if ($stickiness !== Stickiness::DEFAULT ) {
             $seed = $context->findContextValue($stickiness) ?? $this->randomString();
         } else {
             $seed = $context->getCurrentUserId()
@@ -103,7 +105,7 @@ private function calculateStickiness(
                 ?? $this->randomString();
         }
 
-        return $this->stickinessCalculator->calculate($seed, $groupId, $totalWeight);
+        return $this->stickinessCalculator->calculate($seed, $groupId, $totalWeight, $seed = DefaultVariantHandler::VARIANT_HASH_SEED);
     }
 
     private function randomString(): string