From 4bea07f66263bd9914d02fd7cbfba233d5571141 Mon Sep 17 00:00:00 2001
From: Nicholas Dudfield <ndudfield@gmail.com>
Date: Fri, 18 Sep 2026 11:44:49 +0700
Subject: [PATCH] feat(shamap): inject Family PRNG into missing-node walks

NodeFamily forwards Application::getPrng. SHAMapSync draws first-child
offsets from that engine. TestNodeFamily keeps default_prng.
---
 src/test/shamap/common.h               | 7 +++++++
 src/xrpld/shamap/Family.h              | 4 ++++
 src/xrpld/shamap/NodeFamily.h          | 3 +++
 src/xrpld/shamap/detail/NodeFamily.cpp | 6 ++++++
 src/xrpld/shamap/detail/SHAMapSync.cpp | 6 +++---
 5 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/src/test/shamap/common.h b/src/test/shamap/common.h
index 86acc8e2b0..1c2d21b928 100644
--- a/src/test/shamap/common.h
+++ b/src/test/shamap/common.h
@@ -24,6 +24,7 @@
 #include <xrpld/nodestore/Manager.h>
 #include <xrpld/shamap/Family.h>
 #include <xrpl/basics/chrono.h>
+#include <xrpl/basics/random.h>
 
 namespace ripple {
 namespace tests {
@@ -80,6 +81,12 @@ public:
         return j_;
     }
 
+    beast::xor_shift_engine&
+    prng() override
+    {
+        return default_prng();
+    }
+
     std::shared_ptr<FullBelowCache>
     getFullBelowCache() override
     {
diff --git a/src/xrpld/shamap/Family.h b/src/xrpld/shamap/Family.h
index bbb22c273d..ca76b9d95b 100644
--- a/src/xrpld/shamap/Family.h
+++ b/src/xrpld/shamap/Family.h
@@ -25,6 +25,7 @@
 #include <xrpld/shamap/TreeNodeCache.h>
 #include <xrpl/basics/Log.h>
 #include <xrpl/beast/utility/Journal.h>
+#include <xrpl/beast/xor_shift_engine.h>
 #include <cstdint>
 
 namespace ripple {
@@ -53,6 +54,9 @@ public:
     virtual beast::Journal const&
     journal() = 0;
 
+    virtual beast::xor_shift_engine&
+    prng() = 0;
+
     /** Return a pointer to the Family Full Below Cache */
     virtual std::shared_ptr<FullBelowCache>
     getFullBelowCache() = 0;
diff --git a/src/xrpld/shamap/NodeFamily.h b/src/xrpld/shamap/NodeFamily.h
index 4062ea2389..68b51e732f 100644
--- a/src/xrpld/shamap/NodeFamily.h
+++ b/src/xrpld/shamap/NodeFamily.h
@@ -60,6 +60,9 @@ public:
         return j_;
     }
 
+    beast::xor_shift_engine&
+    prng() override;
+
     std::shared_ptr<FullBelowCache>
     getFullBelowCache() override
     {
diff --git a/src/xrpld/shamap/detail/NodeFamily.cpp b/src/xrpld/shamap/detail/NodeFamily.cpp
index faa5c2e360..6ccc7eb873 100644
--- a/src/xrpld/shamap/detail/NodeFamily.cpp
+++ b/src/xrpld/shamap/detail/NodeFamily.cpp
@@ -46,6 +46,12 @@ NodeFamily::NodeFamily(Application& app, CollectorManager& cm)
 {
 }
 
+beast::xor_shift_engine&
+NodeFamily::prng()
+{
+    return app_.getPrng();
+}
+
 void
 NodeFamily::sweep()
 {
diff --git a/src/xrpld/shamap/detail/SHAMapSync.cpp b/src/xrpld/shamap/detail/SHAMapSync.cpp
index 4f93825751..223125c55f 100644
--- a/src/xrpld/shamap/detail/SHAMapSync.cpp
+++ b/src/xrpld/shamap/detail/SHAMapSync.cpp
@@ -235,7 +235,7 @@ SHAMap::gmn_ProcessNodes(MissingNodes& mn, MissingNodes::StackEntry& se)
                 // Switch to processing the child node
                 node = static_cast<SHAMapInnerNode*>(d);
                 nodeID = nodeID.getChildNodeID(branch);
-                firstChild = rand_int(255);
+                firstChild = rand_int(f_.prng(), 255);
                 currentChild = 0;
                 fullBelow = true;
             }
@@ -342,7 +342,7 @@ SHAMap::getMissingNodes(int max, SHAMapSyncFilter* filter)
     MissingNodes::StackEntry pos{
         static_cast<SHAMapInnerNode*>(root_.get()),
         SHAMapNodeID(),
-        rand_int(255),
+        rand_int(f_.prng(), 255),
         0,
         true};
     auto& node = std::get<0>(pos);
@@ -399,7 +399,7 @@ SHAMap::getMissingNodes(int max, SHAMapSyncFilter* filter)
                 for (auto const& [innerNode, nodeId] : mn.resumes_)
                     if (!innerNode->isFullBelow(mn.generation_))
                         mn.stack_.push(std::make_tuple(
-                            innerNode, nodeId, rand_int(255), 0, true));
+                            innerNode, nodeId, rand_int(f_.prng(), 255), 0, true));
 
                 mn.resumes_.clear();
             }