From 7b267c034fdc2c8cb964a763f182ff98a75ba2ac Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter@wuille.net>
Date: Fri, 18 Oct 2024 06:53:44 -0400
Subject: [PATCH] [validation] Add detailed txin/txout information for script
 error messages

Don't just report which script error occurred, but which in which input of which transaction,
and which UTXO was being spent.
---
 src/validation.cpp | 15 ++++++++-------
 src/validation.h   |  2 +-
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/src/validation.cpp b/src/validation.cpp
index 54901b2c58..b8f89f4b88 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2103,14 +2103,15 @@ void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, CTxUndo &txund
     AddCoins(inputs, tx, nHeight);
 }
 
-std::optional<ScriptError> CScriptCheck::operator()() {
+std::optional<std::pair<ScriptError, std::string>> CScriptCheck::operator()() {
     const CScript &scriptSig = ptxTo->vin[nIn].scriptSig;
     const CScriptWitness *witness = &ptxTo->vin[nIn].scriptWitness;
     ScriptError error{SCRIPT_ERR_UNKNOWN_ERROR};
     if (VerifyScript(scriptSig, m_tx_out.scriptPubKey, witness, nFlags, CachingTransactionSignatureChecker(ptxTo, nIn, m_tx_out.nValue, cacheStore, *m_signature_cache, *txdata), &error)) {
         return std::nullopt;
     } else {
-        return error;
+        auto debug_str = strprintf("input %i of %s (wtxid %s), spending %s:%i", nIn, ptxTo->GetHash().ToString(), ptxTo->GetWitnessHash().ToString(), ptxTo->vin[nIn].prevout.hash.ToString(), ptxTo->vin[nIn].prevout.n);
+        return std::make_pair(error, std::move(debug_str));
     }
 }
 
@@ -2214,7 +2215,7 @@ bool CheckInputScripts(const CTransaction& tx, TxValidationState& state,
                         flags & ~STANDARD_NOT_MANDATORY_VERIFY_FLAGS, cacheSigStore, &txdata);
                 auto mandatory_result = check2();
                 if (!mandatory_result.has_value()) {
-                    return state.Invalid(TxValidationResult::TX_NOT_STANDARD, strprintf("non-mandatory-script-verify-flag (%s)", ScriptErrorString(*result)));
+                    return state.Invalid(TxValidationResult::TX_NOT_STANDARD, strprintf("non-mandatory-script-verify-flag (%s)", ScriptErrorString(result->first)), result->second);
                 } else {
                     // If the second check failed, it failed due to a mandatory script verification
                     // flag, but the first check might have failed on a non-mandatory script
@@ -2228,7 +2229,7 @@ bool CheckInputScripts(const CTransaction& tx, TxValidationState& state,
 
             // MANDATORY flag failures correspond to
             // TxValidationResult::TX_CONSENSUS.
-            return state.Invalid(TxValidationResult::TX_CONSENSUS, strprintf("mandatory-script-verify-flag-failed (%s)", ScriptErrorString(*result)));
+            return state.Invalid(TxValidationResult::TX_CONSENSUS, strprintf("mandatory-script-verify-flag-failed (%s)", ScriptErrorString(result->first)), result->second);
         }
     }
 
@@ -2688,7 +2689,7 @@ bool Chainstate::ConnectBlock(const CBlock& block, BlockValidationState& state,
                 // Any transaction validation failure in ConnectBlock is a block consensus failure
                 state.Invalid(BlockValidationResult::BLOCK_CONSENSUS,
                               tx_state.GetRejectReason(), tx_state.GetDebugMessage());
-                LogInfo("Script validation error in block: %s\n", tx_state.GetRejectReason());
+                LogInfo("Script validation error in block: %s\n", state.ToString());
                 return false;
             }
             control.Add(std::move(vChecks));
@@ -2716,8 +2717,8 @@ bool Chainstate::ConnectBlock(const CBlock& block, BlockValidationState& state,
 
     auto parallel_result = control.Complete();
     if (parallel_result.has_value()) {
-        state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, strprintf("mandatory-script-verify-flag-failed (%s)", ScriptErrorString(*parallel_result)));
-        LogInfo("Script validation error in block: %s", state.GetRejectReason());
+        state.Invalid(BlockValidationResult::BLOCK_CONSENSUS, strprintf("mandatory-script-verify-flag-failed (%s)", ScriptErrorString(parallel_result->first)), parallel_result->second);
+        LogInfo("Script validation error in block: %s", state.ToString());
         return false;
     }
     const auto time_4{SteadyClock::now()};
diff --git a/src/validation.h b/src/validation.h
index 14fe145730..6b67dc485b 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -347,7 +347,7 @@ public:
     CScriptCheck(CScriptCheck&&) = default;
     CScriptCheck& operator=(CScriptCheck&&) = default;
 
-    std::optional<ScriptError> operator()();
+    std::optional<std::pair<ScriptError, std::string>> operator()();
 };
 
 // CScriptCheck is used a lot in std::vector, make sure that's efficient