From a8097cd9a6ef827828dca87cd67afead0e2278b9 Mon Sep 17 00:00:00 2001
From: Nicholas Dudfield <ndudfield@gmail.com>
Date: Wed, 18 Mar 2026 17:04:46 +0700
Subject: [PATCH] fix(export): compute emit fee before STTx construction

Mutating the fee via const_cast after STTx construction left a stale
cached getTransactionID(). When the emitted ttEXPORT was serialised
into the emitted directory and later deserialised, the round-tripped
txid differed from the original, causing tefNONDIR_EMIT in
Transactor::preclaim (the emitted dir entry was keyed with the stale
hash).

Build a throwaway STTx with fee=0 to calculate the fee size, then
construct the real STTx with the correct fee from the start.
---
 src/xrpld/app/hook/detail/HookAPI.cpp | 66 ++++++++++++++++++++-------
 1 file changed, 49 insertions(+), 17 deletions(-)

diff --git a/src/xrpld/app/hook/detail/HookAPI.cpp b/src/xrpld/app/hook/detail/HookAPI.cpp
index b4844a16c..ebf9f0a20 100644
--- a/src/xrpld/app/hook/detail/HookAPI.cpp
+++ b/src/xrpld/app/hook/detail/HookAPI.cpp
@@ -1304,14 +1304,61 @@ HookAPI::xport(Slice const& txBlob) const
     Serializer innerSer;
     innerTx->add(innerSer);
 
-    // Build the ttEXPORT wrapper with EmitDetails.
+    // Pre-compute the emit fee so we can set it during STTx
+    // construction.  Mutating the fee after construction via
+    // const_cast leaves a stale cached getTransactionID(), which
+    // breaks the tefNONDIR_EMIT check in Transactor::preclaim
+    // after the emitted tx is serialised and deserialised through
+    // the emitted directory round-trip.
+    //
+    // We build a throwaway STTx with fee=0 just for the size
+    // calculation, then construct the real one with the correct fee.
+    uint64_t emitFee = 0;
+    {
+        STTx tmp(ttEXPORT, [&](auto& obj) {
+            obj[sfAccount] = hookCtx.result.account;
+            obj[sfSequence] = 0u;
+            obj.setFieldVL(sfSigningPubKey, Blob{});
+            obj[sfFirstLedgerSequence] = ledgerSeq + 1;
+            obj[sfLastLedgerSequence] = ledgerSeq + 5;
+            obj[sfFee] = STAmount{0};
+            SerialIter sit(innerSer.slice());
+            obj.set(std::make_unique<STObject>(sit, sfExportedTxn));
+            STObject ed(sfEmitDetails);
+            ed.setFieldU32(
+                sfEmitGeneration, static_cast<uint32_t>(etxn_generation()));
+            {
+                auto const b = etxn_burden();
+                ed.setFieldU64(sfEmitBurden, b ? uint64_t(*b) : 1ULL);
+            }
+            ed.setFieldH256(
+                sfEmitParentTxnID, applyCtx.tx.getTransactionID());
+            ed.setFieldH256(sfEmitNonce, *nonce);
+            ed.setFieldH256(sfEmitHookHash, hookCtx.result.hookHash);
+            if (hookCtx.result.hasCallback)
+                ed.setAccountID(sfEmitCallback, hookCtx.result.account);
+            obj.set(std::move(ed));
+        });
+        Serializer feeSer;
+        tmp.add(feeSer);
+        auto feeResult = etxn_fee_base(feeSer.slice());
+        if (!feeResult)
+        {
+            JLOG(j.trace()) << "HookExport[" << HC_ACC()
+                            << "]: Fee calculation failed for ttEXPORT wrapper";
+            return Unexpected(EXPORT_FAILURE);
+        }
+        emitFee = static_cast<uint64_t>(*feeResult);
+    }
+
+    // Build the ttEXPORT wrapper with the correct fee.
     STTx exportStx(ttEXPORT, [&](auto& obj) {
         obj[sfAccount] = hookCtx.result.account;
         obj[sfSequence] = 0u;
         obj.setFieldVL(sfSigningPubKey, Blob{});
         obj[sfFirstLedgerSequence] = ledgerSeq + 1;
         obj[sfLastLedgerSequence] = ledgerSeq + 5;
-        obj[sfFee] = STAmount{0};  // emitted txns have special fee handling
+        obj[sfFee] = STAmount{emitFee};
 
         // sfExportedTxn inner object
         SerialIter sit(innerSer.slice());
@@ -1336,21 +1383,6 @@ HookAPI::xport(Slice const& txBlob) const
         obj.set(std::move(emitDetails));
     });
 
-    // Calculate proper fee for the emitted transaction.
-    {
-        Serializer feeSer;
-        exportStx.add(feeSer);
-        auto feeResult = etxn_fee_base(feeSer.slice());
-        if (!feeResult)
-        {
-            JLOG(j.trace()) << "HookExport[" << HC_ACC()
-                            << "]: Fee calculation failed for ttEXPORT wrapper";
-            return Unexpected(EXPORT_FAILURE);
-        }
-        const_cast<STTx&>(exportStx).setFieldAmount(
-            sfFee, STAmount{static_cast<uint64_t>(*feeResult)});
-    }
-
     // Preflight the wrapper.
     auto preflightResult = ripple::preflight(
         app, view.rules(), exportStx, ripple::ApplyFlags::tapPREFLIGHT_EMIT, j);