From dc9a67a6931bd5af205af5002fc10b93ee5606fe Mon Sep 17 00:00:00 2001
From: Anthony Towns <aj@erisian.com.au>
Date: Mon, 6 Nov 2023 12:53:03 +1000
Subject: [PATCH] bitcoin-util: introduce evalscript subcommand

---
 src/bitcoin-util.cpp | 243 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 243 insertions(+)

diff --git a/src/bitcoin-util.cpp b/src/bitcoin-util.cpp
index c8f5bc50262e85..ad22ada3778991 100644
--- a/src/bitcoin-util.cpp
+++ b/src/bitcoin-util.cpp
@@ -13,7 +13,12 @@
 #include <common/system.h>
 #include <compat/compat.h>
 #include <core_io.h>
+#include <deploymentinfo.h>
+#include <policy/policy.h>
+#include <script/interpreter.h>
 #include <streams.h>
+#include <univalue.h>
+#include <util/check.h>
 #include <util/exception.h>
 #include <util/strencodings.h>
 #include <util/translation.h>
@@ -34,7 +39,15 @@ static void SetupBitcoinUtilArgs(ArgsManager &argsman)
 
     argsman.AddArg("-version", "Print version and exit", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
 
+    // evalscript options
+    argsman.AddArg("-sigversion", "Specify a script sigversion (base, witness_v0, tapscript).", ArgsManager::ALLOW_ANY, OptionsCategory::COMMAND_OPTIONS);
+    argsman.AddArg("-script_flags", "Specify SCRIPT_VERIFY flags.", ArgsManager::ALLOW_ANY, OptionsCategory::COMMAND_OPTIONS);
+    argsman.AddArg("-tx", "The tx (hex encoded)", ArgsManager::ALLOW_ANY, OptionsCategory::COMMAND_OPTIONS);
+    argsman.AddArg("-input", "The index of the input being spent", ArgsManager::ALLOW_ANY, OptionsCategory::COMMAND_OPTIONS);
+    argsman.AddArg("-spent_output", "The spent prevouts (hex encode TxOut, may be specified multiple times).", ArgsManager::ALLOW_ANY, OptionsCategory::COMMAND_OPTIONS);
+
     argsman.AddCommand("grind", "Perform proof of work on hex header string");
+    argsman.AddCommand("evalscript", "Interpret a bitcoin script", {"-sigversion", "-script_flags", "-tx", "-input", "-spent_output"});
 
     SetupChainParamsBaseOptions(argsman);
 }
@@ -146,6 +159,234 @@ static int Grind(const std::vector<std::string>& args, std::string& strPrint)
     return EXIT_SUCCESS;
 }
 
+static UniValue stack2uv(const std::vector<std::vector<unsigned char>>& stack)
+{
+    UniValue result{UniValue::VARR};
+    for (const auto& v : stack) {
+        result.push_back(HexStr(v));
+    }
+    return result;
+}
+
+static std::string sigver2str(SigVersion sigver)
+{
+    switch(sigver) {
+    case SigVersion::BASE: return "base";
+    case SigVersion::WITNESS_V0: return "witness_v0";
+    case SigVersion::TAPROOT: return "taproot";
+    case SigVersion::TAPSCRIPT: return "tapscript";
+    }
+    return "unknown";
+}
+
+static uint32_t parse_verify_flags(const std::string& strFlags)
+{
+    if (strFlags.empty() || strFlags == "MANDATORY") return MANDATORY_SCRIPT_VERIFY_FLAGS;
+    if (strFlags == "STANDARD") return STANDARD_SCRIPT_VERIFY_FLAGS;
+    if (strFlags == "NONE") return 0;
+
+    unsigned int flags = 0;
+    std::vector<std::string> words = util::SplitString(strFlags, ',');
+
+    for (const std::string& word : words)
+    {
+        if (!g_verify_flag_names.count(word)) continue;
+        flags |= g_verify_flag_names.at(word);
+    }
+    return flags;
+}
+
+//! Public key to be used as internal key for dummy Taproot spends.
+static const std::vector<unsigned char> NUMS_H{ParseHex("50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0")};
+
+namespace {
+/** Dummy signature checker which accepts all signatures. */
+class DummySignatureChecker final : public BaseSignatureChecker
+{
+public:
+    DummySignatureChecker() = default;
+    bool CheckECDSASignature(const std::vector<unsigned char>& sig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const override { return sig.size() != 0; }
+    bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, ScriptExecutionData& execdata, ScriptError* serror) const override { return sig.size() != 0; }
+    bool CheckLockTime(const CScriptNum& nLockTime) const override { return true; }
+    bool CheckSequence(const CScriptNum& nSequence) const override { return true; }
+};
+}
+
+static int EvalScript(const ArgsManager& argsman, const std::vector<std::string>& args, std::string& strPrint)
+{
+    UniValue result{UniValue::VOBJ};
+
+    uint32_t flags{0};
+    PrecomputedTransactionData txdata;
+    ScriptExecutionData execdata;
+
+    std::unique_ptr<const CTransaction> txTo;
+    std::unique_ptr<BaseSignatureChecker> checker;
+
+    SigVersion sigversion = SigVersion::WITNESS_V0;
+
+    if (const auto verstr = argsman.GetArg("-sigversion"); verstr.has_value()) {
+        if (*verstr == "base") {
+            sigversion = SigVersion::BASE;
+        } else if (*verstr == "witness_v0") {
+            sigversion = SigVersion::WITNESS_V0;
+        } else if (*verstr == "tapscript") {
+            sigversion = SigVersion::TAPSCRIPT;
+        } else {
+            strPrint = strprintf("Unknown -sigversion=%s", *verstr);
+            return EXIT_FAILURE;
+        }
+    }
+
+    const auto verifystr = argsman.GetArg("-script_flags");
+    flags = parse_verify_flags(verifystr.value_or(""));
+
+    CScript script{};
+    std::vector<std::vector<unsigned char> > stack{};
+    if (args.size() > 0) {
+        if (IsHex(args[0])) {
+            auto h = ParseHex(args[0]);
+            script = CScript(h.begin(), h.end());
+        } else {
+            script = ParseScript(args[0]);
+        }
+
+        for (size_t i = 1; i < args.size(); ++i) {
+            if (args[i].size() == 0) {
+                stack.push_back({});
+            } else if (IsHex(args[i])) {
+                stack.push_back(ParseHex(args[i]));
+            } else {
+                strPrint = strprintf("Initial stack element not valid hex: %s", args[i]);
+                return EXIT_FAILURE;
+            }
+        }
+    }
+
+    if (const auto txhex = argsman.GetArg("-tx"); txhex.has_value()) {
+        const int input = argsman.GetIntArg("-input", 0);
+        const auto spent_outputs_hex = argsman.GetArgs("-spent_output");
+
+        CMutableTransaction mut_tx;
+        if (!DecodeHexTx(mut_tx, *txhex)) {
+            strPrint = "Could not decode transaction from -tx argument";
+            return EXIT_FAILURE;
+        }
+        txTo = std::make_unique<CTransaction>(mut_tx);
+
+        if (spent_outputs_hex.size() != txTo->vin.size()) {
+            strPrint = "When -tx is specified, must specify exactly one -spent_output for each input";
+            return EXIT_FAILURE;
+        }
+
+        std::vector<CTxOut> spent_outputs;
+        for (const auto& outhex : spent_outputs_hex) {
+            bool ok = false;
+            if (IsHex(outhex)) {
+                CTxOut txout;
+                std::vector<unsigned char> out(ParseHex(outhex));
+                DataStream ss(out);
+                try {
+                    ss >> txout;
+                    if (ss.empty()) {
+                        spent_outputs.push_back(txout);
+                        ok = true;
+                    }
+                } catch (const std::exception&) {
+                    // fall through
+                }
+            }
+            if (!ok) {
+                strPrint = strprintf("Could not parse -spent_output=%s", outhex);
+                return EXIT_FAILURE;
+            }
+        }
+
+        const bool input_in_range = input >= 0 && static_cast<size_t>(input) < spent_outputs.size();
+        CAmount amount = (input_in_range ? spent_outputs.at(input).nValue : 0);
+        txdata.Init(*txTo, std::move(spent_outputs), /*force=*/true);
+        checker = std::make_unique<TransactionSignatureChecker>(txTo.get(), input, amount, txdata, MissingDataBehavior::ASSERT_FAIL);
+
+        if (sigversion == SigVersion::TAPSCRIPT && input >= 0 && input_in_range) {
+            const CTxIn& txin = txTo->vin.at(input);
+            execdata.m_annex_present = false;
+            if (txin.scriptWitness.stack.size() <= 1) {
+                // either key path spend or no witness, so nothing to do here
+            } else {
+                const auto& top = txin.scriptWitness.stack.back();
+                if (top.size() >= 1 && top.at(0) == 0x50) {
+                    execdata.m_annex_hash = (HashWriter{} << top).GetSHA256();
+                    execdata.m_annex_present = true;
+                }
+            }
+            execdata.m_annex_init = true;
+            execdata.m_tapleaf_hash = ComputeTapleafHash(TAPROOT_LEAF_TAPSCRIPT & TAPROOT_LEAF_MASK, script);
+            execdata.m_tapleaf_hash_init = true;
+            execdata.m_validation_weight_left = ::GetSerializeSize(stack) + ::GetSerializeSize(script) + VALIDATION_WEIGHT_OFFSET;
+            execdata.m_validation_weight_left_init = true;
+        }
+    } else {
+        checker = std::make_unique<DummySignatureChecker>();
+    }
+
+    if (sigversion == SigVersion::TAPSCRIPT && !execdata.m_annex_init) {
+        execdata.m_annex_present = false;
+        execdata.m_annex_init = true;
+        execdata.m_tapleaf_hash = uint256::ZERO;
+        execdata.m_tapleaf_hash_init = true;
+        execdata.m_validation_weight_left = ::GetSerializeSize(stack) + ::GetSerializeSize(script) + VALIDATION_WEIGHT_OFFSET;
+        execdata.m_validation_weight_left_init = true;
+    }
+
+    ScriptError serror{};
+
+    UniValue uv_flags{UniValue::VARR};
+    for (const auto& el : GetScriptFlagNames(flags)) {
+        uv_flags.push_back(el);
+    }
+    UniValue uv_script{UniValue::VOBJ};
+    ScriptToUniv(script, uv_script);
+    result.pushKV("script", uv_script);
+    result.pushKV("sigversion", sigver2str(sigversion));
+    result.pushKV("script_flags", uv_flags);
+
+    std::optional<bool> opsuccess_check;
+    if (sigversion == SigVersion::TAPSCRIPT) {
+        opsuccess_check = CheckTapscriptOpSuccess(script, flags, &serror);
+    }
+
+    bool success = (opsuccess_check.has_value() ? *opsuccess_check : EvalScript(stack, script, flags, *Assert(checker), sigversion, execdata, &serror));
+    if (opsuccess_check.has_value()) {
+         result.pushKV("opsuccess_found", true);
+    } else if (success) {
+        if (stack.empty() || !CastToBool(stack.back())) {
+            success = false;
+            serror = SCRIPT_ERR_EVAL_FALSE;
+        } else if (stack.size() > 1) {
+            if (sigversion == SigVersion::WITNESS_V0 || sigversion == SigVersion::TAPSCRIPT) {
+                success = false;
+                serror = SCRIPT_ERR_CLEANSTACK;
+            } else if ((flags & SCRIPT_VERIFY_CLEANSTACK) != 0) {
+                success = false;
+                serror = SCRIPT_ERR_CLEANSTACK;
+            }
+        }
+    }
+
+    result.pushKV("stack-after", stack2uv(stack));
+
+    result.pushKV("sigop-count", (sigversion == SigVersion::TAPSCRIPT ? 0 : script.GetSigOpCount(true)));
+
+    result.pushKV("success", success);
+    if (!success) {
+        result.pushKV("error", ScriptErrorString(serror));
+    }
+
+    strPrint = result.write(2);
+
+    return EXIT_SUCCESS;
+}
+
 MAIN_FUNCTION
 {
     ArgsManager& args = gArgs;
@@ -175,6 +416,8 @@ MAIN_FUNCTION
     try {
         if (cmd->command == "grind") {
             ret = Grind(cmd->args, strPrint);
+        } else if (cmd->command == "evalscript") {
+            ret = EvalScript(args, cmd->args, strPrint);
         } else {
             assert(false); // unknown command should be caught earlier
         }