From 092c978a42e8f4a02291b994713505ba8aac8b28 Mon Sep 17 00:00:00 2001
From: glozow <gloriajzhao@gmail.com>
Date: Tue, 16 Apr 2024 11:58:25 +0100
Subject: [PATCH] [txpackages] add canonical way to get hash of package

---
 src/policy/packages.cpp      | 18 +++++++
 src/policy/packages.h        |  5 ++
 src/test/txpackage_tests.cpp | 98 +++++++++++++++++++++++++++++++++++-
 3 files changed, 120 insertions(+), 1 deletion(-)

diff --git a/src/policy/packages.cpp b/src/policy/packages.cpp
index 3a63a9fe464..99d2a6d514e 100644
--- a/src/policy/packages.cpp
+++ b/src/policy/packages.cpp
@@ -147,3 +147,21 @@ bool IsChildWithParentsTree(const Package& package)
         return true;
     });
 }
+
+uint256 GetPackageHash(const std::vector<CTransactionRef>& transactions)
+{
+    // Create a vector of the wtxids.
+    std::vector<Wtxid> wtxids_copy;
+    std::transform(transactions.cbegin(), transactions.cend(), std::back_inserter(wtxids_copy),
+        [](const auto& tx){ return tx->GetWitnessHash(); });
+
+    // Sort in ascending order
+    std::sort(wtxids_copy.begin(), wtxids_copy.end(), [](const auto& lhs, const auto& rhs) { return lhs.GetHex() < rhs.GetHex(); });
+
+    // Get sha256 hash of the wtxids concatenated in this order
+    HashWriter hashwriter;
+    for (const auto& wtxid : wtxids_copy) {
+        hashwriter << wtxid;
+    }
+    return hashwriter.GetSHA256();
+}
diff --git a/src/policy/packages.h b/src/policy/packages.h
index 537d8476e2d..30503201226 100644
--- a/src/policy/packages.h
+++ b/src/policy/packages.h
@@ -88,4 +88,9 @@ bool IsChildWithParents(const Package& package);
  * other (the package is a "tree").
  */
 bool IsChildWithParentsTree(const Package& package);
+
+/** Get the hash of these transactions' wtxids, concatenated in lexicographical order (treating the
+ * wtxids as little endian encoded uint256, smallest to largest). */
+uint256 GetPackageHash(const std::vector<CTransactionRef>& transactions);
+
 #endif // BITCOIN_POLICY_PACKAGES_H
diff --git a/src/test/txpackage_tests.cpp b/src/test/txpackage_tests.cpp
index b948ea8acba..8112f5f6856 100644
--- a/src/test/txpackage_tests.cpp
+++ b/src/test/txpackage_tests.cpp
@@ -8,9 +8,12 @@
 #include <policy/policy.h>
 #include <primitives/transaction.h>
 #include <script/script.h>
+#include <serialize.h>
+#include <streams.h>
 #include <test/util/random.h>
 #include <test/util/script.h>
 #include <test/util/setup_common.h>
+#include <util/strencodings.h>
 #include <test/util/txmempool.h>
 #include <validation.h>
 
@@ -40,6 +43,93 @@ inline CTransactionRef create_placeholder_tx(size_t num_inputs, size_t num_outpu
     return MakeTransactionRef(mtx);
 }
 
+// Create a Wtxid from a hex string
+inline Wtxid WtxidFromString(std::string_view str)
+{
+    return Wtxid::FromUint256(uint256S(str.data()));
+}
+
+BOOST_FIXTURE_TEST_CASE(package_hash_tests, TestChain100Setup)
+{
+    // Random real segwit transaction
+    DataStream stream_1{
+        ParseHex("02000000000101964b8aa63509579ca6086e6012eeaa4c2f4dd1e283da29b67c8eea38b3c6fd220000000000fdffffff0294c618000000000017a9145afbbb42f4e83312666d0697f9e66259912ecde38768fa2c0000000000160014897388a0889390fd0e153a22bb2cf9d8f019faf50247304402200547406380719f84d68cf4e96cc3e4a1688309ef475b150be2b471c70ea562aa02206d255f5acc40fd95981874d77201d2eb07883657ce1c796513f32b6079545cdf0121023ae77335cefcb5ab4c1dc1fb0d2acfece184e593727d7d5906c78e564c7c11d125cf0c00"),
+    };
+    CTransaction tx_1(deserialize, TX_WITH_WITNESS, stream_1);
+    CTransactionRef ptx_1{MakeTransactionRef(tx_1)};
+
+    // Random real nonsegwit transaction
+    DataStream stream_2{
+        ParseHex("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"),
+    };
+    CTransaction tx_2(deserialize, TX_WITH_WITNESS, stream_2);
+    CTransactionRef ptx_2{MakeTransactionRef(tx_2)};
+
+    // Random real segwit transaction
+    DataStream stream_3{
+        ParseHex("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"),
+    };
+    CTransaction tx_3(deserialize, TX_WITH_WITNESS, stream_3);
+    CTransactionRef ptx_3{MakeTransactionRef(tx_3)};
+
+    // It's easy to see that wtxids are sorted in lexicographical order:
+    Wtxid wtxid_1{WtxidFromString("0x85cd1a31eb38f74ed5742ec9cb546712ab5aaf747de28a9168b53e846cbda17f")};
+    Wtxid wtxid_2{WtxidFromString("0xb4749f017444b051c44dfd2720e88f314ff94f3dd6d56d40ef65854fcd7fff6b")};
+    Wtxid wtxid_3{WtxidFromString("0xe065bac15f62bb4e761d761db928ddee65a47296b2b776785abb912cdec474e3")};
+    BOOST_CHECK_EQUAL(tx_1.GetWitnessHash(), wtxid_1);
+    BOOST_CHECK_EQUAL(tx_2.GetWitnessHash(), wtxid_2);
+    BOOST_CHECK_EQUAL(tx_3.GetWitnessHash(), wtxid_3);
+
+    BOOST_CHECK(wtxid_1.GetHex() < wtxid_2.GetHex());
+    BOOST_CHECK(wtxid_2.GetHex() < wtxid_3.GetHex());
+
+    // The txids are not (we want to test that sorting and hashing use wtxid, not txid):
+    Txid txid_1{TxidFromString("0xbd0f71c1d5e50589063e134fad22053cdae5ab2320db5bf5e540198b0b5a4e69")};
+    Txid txid_2{TxidFromString("0xb4749f017444b051c44dfd2720e88f314ff94f3dd6d56d40ef65854fcd7fff6b")};
+    Txid txid_3{TxidFromString("0xee707be5201160e32c4fc715bec227d1aeea5940fb4295605e7373edce3b1a93")};
+    BOOST_CHECK_EQUAL(tx_1.GetHash(), txid_1);
+    BOOST_CHECK_EQUAL(tx_2.GetHash(), txid_2);
+    BOOST_CHECK_EQUAL(tx_3.GetHash(), txid_3);
+
+    BOOST_CHECK(txid_2.GetHex() < txid_1.GetHex());
+
+    BOOST_CHECK(txid_1.ToUint256() != wtxid_1.ToUint256());
+    BOOST_CHECK(txid_2.ToUint256() == wtxid_2.ToUint256());
+    BOOST_CHECK(txid_3.ToUint256() != wtxid_3.ToUint256());
+
+    // We are testing that both functions compare using GetHex() and not uint256.
+    // (in this pair of wtxids, hex string order != uint256 order)
+    BOOST_CHECK(wtxid_2 < wtxid_1);
+    // (in this pair of wtxids, hex string order == uint256 order)
+    BOOST_CHECK(wtxid_2 < wtxid_3);
+
+    // All permutations of the package containing ptx_1, ptx_2, ptx_3 have the same package hash
+    std::vector<CTransactionRef> package_123{ptx_1, ptx_2, ptx_3};
+    std::vector<CTransactionRef> package_132{ptx_1, ptx_3, ptx_2};
+    std::vector<CTransactionRef> package_231{ptx_2, ptx_3, ptx_1};
+    std::vector<CTransactionRef> package_213{ptx_2, ptx_1, ptx_3};
+    std::vector<CTransactionRef> package_312{ptx_3, ptx_1, ptx_2};
+    std::vector<CTransactionRef> package_321{ptx_3, ptx_2, ptx_1};
+
+    uint256 calculated_hash_123 = (HashWriter() << wtxid_1 << wtxid_2 << wtxid_3).GetSHA256();
+
+    uint256 hash_if_by_txid = (HashWriter() << wtxid_2 << wtxid_1 << wtxid_3).GetSHA256();
+    BOOST_CHECK(hash_if_by_txid != calculated_hash_123);
+
+    uint256 hash_if_use_txid = (HashWriter() << txid_2 << txid_1 << txid_3).GetSHA256();
+    BOOST_CHECK(hash_if_use_txid != calculated_hash_123);
+
+    uint256 hash_if_use_int_order = (HashWriter() << wtxid_2 << wtxid_1 << wtxid_3).GetSHA256();
+    BOOST_CHECK(hash_if_use_int_order != calculated_hash_123);
+
+    BOOST_CHECK_EQUAL(calculated_hash_123, GetPackageHash(package_123));
+    BOOST_CHECK_EQUAL(calculated_hash_123, GetPackageHash(package_132));
+    BOOST_CHECK_EQUAL(calculated_hash_123, GetPackageHash(package_231));
+    BOOST_CHECK_EQUAL(calculated_hash_123, GetPackageHash(package_213));
+    BOOST_CHECK_EQUAL(calculated_hash_123, GetPackageHash(package_312));
+    BOOST_CHECK_EQUAL(calculated_hash_123, GetPackageHash(package_321));
+}
+
 BOOST_FIXTURE_TEST_CASE(package_sanitization_tests, TestChain100Setup)
 {
     // Packages can't have more than 25 transactions.
@@ -190,6 +280,9 @@ BOOST_FIXTURE_TEST_CASE(noncontextual_package_tests, TestChain100Setup)
         BOOST_CHECK_EQUAL(state.GetRejectReason(), "package-not-sorted");
         BOOST_CHECK(IsChildWithParents({tx_parent, tx_child}));
         BOOST_CHECK(IsChildWithParentsTree({tx_parent, tx_child}));
+        BOOST_CHECK(GetPackageHash({tx_parent}) != GetPackageHash({tx_child}));
+        BOOST_CHECK(GetPackageHash({tx_child, tx_child}) != GetPackageHash({tx_child}));
+        BOOST_CHECK(GetPackageHash({tx_child, tx_parent}) != GetPackageHash({tx_child, tx_child}));
     }
 
     // 24 Parents and 1 Child
@@ -450,6 +543,8 @@ BOOST_FIXTURE_TEST_CASE(package_witness_swap_tests, TestChain100Setup)
     BOOST_CHECK_EQUAL(ptx_child1->GetHash(), ptx_child2->GetHash());
     // child1 and child2 have different wtxids
     BOOST_CHECK(ptx_child1->GetWitnessHash() != ptx_child2->GetWitnessHash());
+    // Check that they have different package hashes
+    BOOST_CHECK(GetPackageHash({ptx_parent, ptx_child1}) != GetPackageHash({ptx_parent, ptx_child2}));
 
     // Try submitting Package1{parent, child1} and Package2{parent, child2} where the children are
     // same-txid-different-witness.
@@ -503,7 +598,8 @@ BOOST_FIXTURE_TEST_CASE(package_witness_swap_tests, TestChain100Setup)
                                                         /*output_destination=*/grandchild_locking_script,
                                                         /*output_amount=*/CAmount(47 * COIN), /*submit=*/false);
     CTransactionRef ptx_grandchild = MakeTransactionRef(mtx_grandchild);
-
+    // Check that they have different package hashes
+    BOOST_CHECK(GetPackageHash({ptx_child1, ptx_grandchild}) != GetPackageHash({ptx_child2, ptx_grandchild}));
     // We already submitted child1 above.
     {
         Package package_child2_grandchild{ptx_child2, ptx_grandchild};