From d2611e9d97be695703afce142ab81760e13a0a45 Mon Sep 17 00:00:00 2001
From: Gregory Sanders <gsanders87@gmail.com>
Date: Wed, 3 Oct 2018 14:41:03 +0900
Subject: [PATCH] CreateTransaction: Assume minimum p2sh-p2wpkh spend size for
 unknown change

---
 src/wallet/test/wallet_tests.cpp | 44 ++++++++++++++++++++++++++++++++
 src/wallet/wallet.h              |  3 +++
 test/functional/rpc_psbt.py      |  4 +++
 3 files changed, 51 insertions(+)

diff --git a/src/wallet/test/wallet_tests.cpp b/src/wallet/test/wallet_tests.cpp
index fc3be2b6a..cba2925ed 100644
--- a/src/wallet/test/wallet_tests.cpp
+++ b/src/wallet/test/wallet_tests.cpp
@@ -16,6 +16,7 @@
 #include <validation.h>
 #include <wallet/coincontrol.h>
 #include <wallet/test/wallet_test_fixture.h>
+#include <policy/policy.h>
 
 #include <boost/test/unit_test.hpp>
 #include <univalue.h>
@@ -515,4 +516,47 @@ BOOST_FIXTURE_TEST_CASE(dummy_input_size_test, TestChain100Setup)
     BOOST_CHECK_EQUAL(CalculateNestedKeyhashInputSize(true), DUMMY_NESTED_P2WPKH_INPUT_SIZE);
 }
 
+// Explicit calculation which is used to test the wallet constant
+// We get the same virtual size due to rounding(weight/4) for both use_max_sig values
+static size_t CalculateNestedKeyhashInputSize(bool use_max_sig)
+{
+    // Generate ephemeral valid pubkey
+    CKey key;
+    key.MakeNewKey(true);
+    CPubKey pubkey = key.GetPubKey();
+
+    // Generate pubkey hash
+    uint160 key_hash(Hash160(pubkey.begin(), pubkey.end()));
+
+    // Create inner-script to enter into keystore. Key hash can't be 0...
+    CScript inner_script = CScript() << OP_0 << std::vector<unsigned char>(key_hash.begin(), key_hash.end());
+
+    // Create outer P2SH script for the output
+    uint160 script_id(Hash160(inner_script.begin(), inner_script.end()));
+    CScript script_pubkey = CScript() << OP_HASH160 << std::vector<unsigned char>(script_id.begin(), script_id.end()) << OP_EQUAL;
+
+    // Add inner-script to key store and key to watchonly
+    CBasicKeyStore keystore;
+    keystore.AddCScript(inner_script);
+    keystore.AddKeyPubKey(key, pubkey);
+
+    // Fill in dummy signatures for fee calculation.
+    SignatureData sig_data;
+
+    if (!ProduceSignature(keystore, use_max_sig ? DUMMY_MAXIMUM_SIGNATURE_CREATOR : DUMMY_SIGNATURE_CREATOR, script_pubkey, sig_data)) {
+        // We're hand-feeding it correct arguments; shouldn't happen
+        assert(false);
+    }
+
+    CTxIn tx_in;
+    UpdateInput(tx_in, sig_data);
+    return (size_t)GetVirtualTransactionInputSize(tx_in);
+}
+
+BOOST_FIXTURE_TEST_CASE(dummy_input_size_test, TestChain100Setup)
+{
+    BOOST_CHECK_EQUAL(CalculateNestedKeyhashInputSize(false), DUMMY_NESTED_P2WPKH_INPUT_SIZE);
+    BOOST_CHECK_EQUAL(CalculateNestedKeyhashInputSize(true), DUMMY_NESTED_P2WPKH_INPUT_SIZE);
+}
+
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index f4f0156b4..968d09fbe 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -95,6 +95,9 @@ constexpr CAmount HIGH_MAX_TX_FEE{100 * HIGH_TX_FEE_PER_KB};
 //! Pre-calculated constants for input size estimation in *virtual size*
 static constexpr size_t DUMMY_NESTED_P2WPKH_INPUT_SIZE = 91;
 
+//! Pre-calculated constants for input size estimation in *virtual size*
+static constexpr size_t DUMMY_NESTED_P2WPKH_INPUT_SIZE = 91;
+
 class CCoinControl;
 class COutput;
 class CScript;
diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index 5c53cf9ac..8134213b3 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -256,6 +256,10 @@ class PSBTTest(BitcoinTestFramework):
         # We don't care about the decode result, but decoding must succeed.
         self.nodes[0].decodepsbt(double_processed_psbt["psbt"])
 
+        # Make sure change address wallet does not have P2SH innerscript access to results in success
+        # when attempting BnB coin selection
+        self.nodes[0].walletcreatefundedpsbt([], [{self.nodes[2].getnewaddress():unspent["amount"]+1}], block_height+2, {"changeAddress":self.nodes[1].getnewaddress()}, False)
+
         # BIP 174 Test Vectors
 
         # Check that unknown values are just passed through