Merge bitcoin/bitcoin#24560: wallet: Use single FastRandomContext when creating a wallet tx

fa7deaa0464576a229b5a6ab13ad033c16d0dada wallet: Pass FastRandomContext& to coin selection (MarcoFalke)
77773b061cb13229a8afb46f6f3ab89fc70eabe3 wallet: Pass FastRandomContext& to DiscourageFeeSniping (MarcoFalke)

Pull request description:

  Passing around a single randomness context shouldn't come with any downsides, but documents better where randomness is used and allows the unit test to be deterministic, if they wish to be so.

ACKs for top commit:
  achow101:
    ACK fa7deaa0464576a229b5a6ab13ad033c16d0dada
  promag:
    Code review ACK fa7deaa0464576a229b5a6ab13ad033c16d0dada.
  glozow:
    light code review ACK fa7deaa0464576a229b5a6ab13ad033c16d0dada

Tree-SHA512: c16287708cc82ce58311710595d0127af42fb156c93fbcaa5bde634ce323d325f4d8c99a74af24423ab22b5ad58163dd771e8b1a0e7d6bff39c9fb2a1cb21bc7

1 files changed, 7 insertions, 9 deletions

diff --git a/src/wallet/coinselection.cpp b/src/wallet/coinselection.cpp
index 20891a3e28..2df66ac15b 100644
--- a/src/wallet/coinselection.cpp
+++ b/src/wallet/coinselection.cpp
@@ -165,14 +165,14 @@ std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_poo
     return result;
 }
 
-std::optional<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value)
+std::optional<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value, FastRandomContext& rng)
 {
     SelectionResult result(target_value);
 
     std::vector<size_t> indexes;
     indexes.resize(utxo_pool.size());
     std::iota(indexes.begin(), indexes.end(), 0);
-    Shuffle(indexes.begin(), indexes.end(), FastRandomContext());
+    Shuffle(indexes.begin(), indexes.end(), rng);
 
     CAmount selected_eff_value = 0;
     for (const size_t i : indexes) {
@@ -187,7 +187,7 @@ std::optional<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& ut
     return std::nullopt;
 }
 
-static void ApproximateBestSubset(const std::vector<OutputGroup>& groups, const CAmount& nTotalLower, const CAmount& nTargetValue,
+static void ApproximateBestSubset(FastRandomContext& insecure_rand, const std::vector<OutputGroup>& groups, const CAmount& nTotalLower, const CAmount& nTargetValue,
                                   std::vector<char>& vfBest, CAmount& nBest, int iterations = 1000)
 {
     std::vector<char> vfIncluded;
@@ -195,8 +195,6 @@ static void ApproximateBestSubset(const std::vector<OutputGroup>& groups, const
     vfBest.assign(groups.size(), true);
     nBest = nTotalLower;
 
-    FastRandomContext insecure_rand;
-
     for (int nRep = 0; nRep < iterations && nBest != nTargetValue; nRep++)
     {
         vfIncluded.assign(groups.size(), false);
@@ -233,7 +231,7 @@ static void ApproximateBestSubset(const std::vector<OutputGroup>& groups, const
     }
 }
 
-std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue)
+std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue, FastRandomContext& rng)
 {
     SelectionResult result(nTargetValue);
 
@@ -242,7 +240,7 @@ std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups,
     std::vector<OutputGroup> applicable_groups;
     CAmount nTotalLower = 0;
 
-    Shuffle(groups.begin(), groups.end(), FastRandomContext());
+    Shuffle(groups.begin(), groups.end(), rng);
 
     for (const OutputGroup& group : groups) {
         if (group.GetSelectionAmount() == nTargetValue) {
@@ -274,9 +272,9 @@ std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups,
     std::vector<char> vfBest;
     CAmount nBest;
 
-    ApproximateBestSubset(applicable_groups, nTotalLower, nTargetValue, vfBest, nBest);
+    ApproximateBestSubset(rng, applicable_groups, nTotalLower, nTargetValue, vfBest, nBest);
     if (nBest != nTargetValue && nTotalLower >= nTargetValue + MIN_CHANGE) {
-        ApproximateBestSubset(applicable_groups, nTotalLower, nTargetValue + MIN_CHANGE, vfBest, nBest);
+        ApproximateBestSubset(rng, applicable_groups, nTotalLower, nTargetValue + MIN_CHANGE, vfBest, nBest);
     }
 
     // If we have a bigger coin and (either the stochastic approximation didn't find a good solution,