Function TestNode

src/test/fuzz/miniscript.cpp:1030–1193

Perform various applicable tests on a miniscript Node. */

/** Perform various applicable tests on a miniscript Node. */
void TestNode(const MsCtx script_ctx, const std::optional<Node>& node, FuzzedDataProvider& provider)
{
    if (!node) return;

    // Check that it roundtrips to text representation
    const ParserContext parser_ctx{script_ctx};
    std::optional<std::string> str{node->ToString(parser_ctx)};
    assert(str);
    auto parsed = miniscript::FromString(*str, parser_ctx);
    assert(parsed);
    assert(*parsed == *node);

    // Check consistency between script size estimation and real size.
    auto script = node->ToScript(parser_ctx);
    assert(node->ScriptSize() == script.size());

    // Check consistency of "x" property with the script (type K is excluded, because it can end
    // with a push of a key, which could match these opcodes).
    if (!(node->GetType() << "K"_mst)) {
        bool ends_in_verify = !(node->GetType() << "x"_mst);
        assert(ends_in_verify == (script.back() == OP_CHECKSIG || script.back() == OP_CHECKMULTISIG || script.back() == OP_EQUAL || script.back() == OP_NUMEQUAL));
    }

    // The rest of the checks only apply when testing a valid top-level script.
    if (!node->IsValidTopLevel()) return;

    // Check roundtrip to script
    auto decoded = miniscript::FromScript(script, parser_ctx);
    assert(decoded);
    // Note we can't use *decoded == *node because the miniscript representation may differ, so we check that:
    // - The script corresponding to that decoded form matches exactly
    // - The type matches exactly
    assert(decoded->ToScript(parser_ctx) == script);
    assert(decoded->GetType() == node->GetType());

    // Optionally pad the script or the witness in order to increase the sensitivity of the tests of
    // the resources limits logic.
    CScriptWitness witness_mal, witness_nonmal;
    if (provider.ConsumeBool()) {
        // Under P2WSH, optionally pad the script with OP_NOPs to max op the ops limit of the constructed script.
        // This makes the script obviously not actually miniscript-compatible anymore, but the
        // signatures constructed in this test don't commit to the script anyway, so the same
        // miniscript satisfier will work. This increases the sensitivity of the test to the ops
        // counting logic being too low, especially for simple scripts.
        // Do this optionally because we're not solely interested in cases where the number of ops is
        // maximal.
        // Do not pad more than what would cause MAX_STANDARD_P2WSH_SCRIPT_SIZE to be reached, however,
        // as that also invalidates scripts.
        const auto node_ops{node->GetOps()};
        if (!IsTapscript(script_ctx) && node_ops && *node_ops < MAX_OPS_PER_SCRIPT
            && node->ScriptSize() < MAX_STANDARD_P2WSH_SCRIPT_SIZE) {
            int add = std::min<int>(
                MAX_OPS_PER_SCRIPT - *node_ops,
                MAX_STANDARD_P2WSH_SCRIPT_SIZE - node->ScriptSize());
            for (int i = 0; i < add; ++i) script.push_back(OP_NOP);
        }

        // Under Tapscript, optionally pad the stack up to the limit minus the calculated maximum execution stack