wasmtime.hh

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#ifndef WASMTIME_HH
#define WASMTIME_HH
 
#include <any>
#include <array>
#include <cstdio>
#include <initializer_list>
#include <iosfwd>
#include <limits>
#include <memory>
#include <optional>
#include <ostream>
#include <variant>
#include <vector>
 
#include <wasmtime.h>
#include <wasmtime/config.hh>
#include <wasmtime/engine.hh>
#include <wasmtime/error.hh>
#include <wasmtime/module.hh>
#include <wasmtime/store.hh>
#include <wasmtime/trap.hh>
#include <wasmtime/types.hh>
#include <wasmtime/wasi.hh>
#include <wasmtime/val.hh>
 
namespace wasmtime {
 
class Caller;
class Func;
class Global;
class Instance;
class Memory;
class Table;
 
typedef std::variant<Func, Global, Memory, Table> Extern;
 
template <typename Params, typename Results> class TypedFunc;
 
class Caller {
  friend class Func;
  friend class Store;
  wasmtime_caller_t *ptr;
  Caller(wasmtime_caller_t *ptr) : ptr(ptr) {}
 
public:
  std::optional<Extern> get_export(std::string_view name);
 
  Store::Context context() { return this; }
};
 
inline Store::Context::Context(Caller &caller)
    : Context(wasmtime_caller_context(caller.ptr)) {}
inline Store::Context::Context(Caller *caller) : Context(*caller) {}
 
namespace detail {
 
template <typename T> struct WasmType { static const bool valid = false; };
 
// NOLINTNEXTLINE
#define NATIVE_WASM_TYPE(native, valkind, field)                               \
  template <> struct WasmType<native> {                                        \
    static const bool valid = true;                                            \
    static const ValKind kind = ValKind::valkind;                              \
    static void store(Store::Context cx, wasmtime_val_raw_t *p,                \
                      const native &t) {                                       \
      p->field = t;                                                            \
    }                                                                          \
    static native load(Store::Context cx, wasmtime_val_raw_t *p) {             \
      return p->field;                                                         \
    }                                                                          \
  };
 
NATIVE_WASM_TYPE(int32_t, I32, i32)
NATIVE_WASM_TYPE(uint32_t, I32, i32)
NATIVE_WASM_TYPE(int64_t, I64, i64)
NATIVE_WASM_TYPE(uint64_t, I64, i64)
NATIVE_WASM_TYPE(float, F32, f32)
NATIVE_WASM_TYPE(double, F64, f64)
 
#undef NATIVE_WASM_TYPE
 
template <> struct WasmType<std::optional<ExternRef>> {
  static const bool valid = true;
  static const ValKind kind = ValKind::ExternRef;
  static void store(Store::Context cx, wasmtime_val_raw_t *p,
                    const std::optional<ExternRef> &ref) {
    if (ref) {
      p->externref = wasmtime_externref_to_raw(cx.raw_context(), ref->raw());
    } else {
      p->externref = 0;
    }
  }
  static std::optional<ExternRef> load(Store::Context cx,
                                       wasmtime_val_raw_t *p) {
    if (p->externref == 0) {
      return std::nullopt;
    }
    wasmtime_externref_t val;
    wasmtime_externref_from_raw(cx.raw_context(), p->externref, &val);
    return ExternRef(val);
  }
};
 
template <> struct WasmType<V128> {
  static const bool valid = true;
  static const ValKind kind = ValKind::V128;
  static void store(Store::Context cx, wasmtime_val_raw_t *p, const V128 &t) {
    memcpy(&p->v128[0], &t.v128[0], sizeof(wasmtime_v128));
  }
  static V128 load(Store::Context cx, wasmtime_val_raw_t *p) { return p->v128; }
};
 
template <typename T> struct WasmTypeList {
  static const bool valid = WasmType<T>::valid;
  static const size_t size = 1;
  static bool matches(ValType::ListRef types) {
    return WasmTypeList<std::tuple<T>>::matches(types);
  }
  static void store(Store::Context cx, wasmtime_val_raw_t *storage,
                    const T &t) {
    WasmType<T>::store(cx, storage, t);
  }
  static T load(Store::Context cx, wasmtime_val_raw_t *storage) {
    return WasmType<T>::load(cx, storage);
  }
  static std::vector<ValType> types() { return {WasmType<T>::kind}; }
};
 
template <> struct WasmTypeList<std::monostate> {
  static const bool valid = true;
  static const size_t size = 0;
  static bool matches(ValType::ListRef types) { return types.size() == 0; }
  static void store(Store::Context cx, wasmtime_val_raw_t *storage,
                    const std::monostate &t) {}
  static std::monostate load(Store::Context cx, wasmtime_val_raw_t *storage) {
    return std::monostate();
  }
  static std::vector<ValType> types() { return {}; }
};
 
template <typename... T> struct WasmTypeList<std::tuple<T...>> {
  static const bool valid = (WasmType<T>::valid && ...);
  static const size_t size = sizeof...(T);
  static bool matches(ValType::ListRef types) {
    if (types.size() != size) {
      return false;
    }
    size_t n = 0;
    return ((WasmType<T>::kind == types.begin()[n++].kind()) && ...);
  }
  static void store(Store::Context cx, wasmtime_val_raw_t *storage,
                    const std::tuple<T...> &t) {
    size_t n = 0;
    std::apply(
        [&](const auto &...val) {
          (WasmType<T>::store(cx, &storage[n++], val), ...); // NOLINT
        },
        t);
  }
  static std::tuple<T...> load(Store::Context cx, wasmtime_val_raw_t *storage) {
    size_t n = 0;
    return std::tuple<T...>{WasmType<T>::load(cx, &storage[n++])...}; // NOLINT
  }
  static std::vector<ValType> types() { return {WasmType<T>::kind...}; }
};
 
template <typename R> struct WasmHostRet {
  using Results = WasmTypeList<R>;
 
  template <typename F, typename... A>
  static std::optional<Trap> invoke(F f, Caller cx, wasmtime_val_raw_t *raw,
                                    A... args) {
    auto ret = f(args...);
    Results::store(cx, raw, ret);
    return std::nullopt;
  }
};
 
template <> struct WasmHostRet<void> {
  using Results = WasmTypeList<std::tuple<>>;
 
  template <typename F, typename... A>
  static std::optional<Trap> invoke(F f, Caller cx, wasmtime_val_raw_t *raw,
                                    A... args) {
    f(args...);
    return std::nullopt;
  }
};
 
// Alternative method of returning "nothing" (also enables `std::monostate` in
// the `R` type of `Result` below)
template <> struct WasmHostRet<std::monostate> : public WasmHostRet<void> {};
 
template <typename R> struct WasmHostRet<Result<R, Trap>> {
  using Results = WasmTypeList<R>;
 
  template <typename F, typename... A>
  static std::optional<Trap> invoke(F f, Caller cx, wasmtime_val_raw_t *raw,
                                    A... args) {
    Result<R, Trap> ret = f(args...);
    if (!ret) {
      return ret.err();
    }
    Results::store(cx, raw, ret.ok());
    return std::nullopt;
  }
};
 
template <typename F, typename = void> struct WasmHostFunc;
 
template <typename R, typename... A> struct WasmHostFunc<R (*)(A...)> {
  using Params = WasmTypeList<std::tuple<A...>>;
  using Results = typename WasmHostRet<R>::Results;
 
  template <typename F>
  static std::optional<Trap> invoke(F &f, Caller cx, wasmtime_val_raw_t *raw) {
    auto params = Params::load(cx, raw);
    return std::apply(
        [&](const auto &...val) {
          return WasmHostRet<R>::invoke(f, cx, raw, val...);
        },
        params);
  }
};
 
template <typename R, typename... A>
struct WasmHostFunc<R (*)(Caller, A...)> : public WasmHostFunc<R (*)(A...)> {
  // Override `invoke` here to pass the `cx` as the first parameter
  template <typename F>
  static std::optional<Trap> invoke(F &f, Caller cx, wasmtime_val_raw_t *raw) {
    auto params = WasmTypeList<std::tuple<A...>>::load(cx, raw);
    return std::apply(
        [&](const auto &...val) {
          return WasmHostRet<R>::invoke(f, cx, raw, cx, val...);
        },
        params);
  }
};
 
template <typename R, typename C, typename... A>
struct WasmHostFunc<R (C::*)(A...)> : public WasmHostFunc<R (*)(A...)> {};
 
template <typename R, typename C, typename... A>
struct WasmHostFunc<R (C::*)(A...) const> : public WasmHostFunc<R (*)(A...)> {};
 
template <typename R, typename C, typename... A>
struct WasmHostFunc<R (C::*)(Caller, A...)>
    : public WasmHostFunc<R (*)(Caller, A...)> {};
 
template <typename R, typename C, typename... A>
struct WasmHostFunc<R (C::*)(Caller, A...) const>
    : public WasmHostFunc<R (*)(Caller, A...)> {};
 
template <typename T>
struct WasmHostFunc<T, std::void_t<decltype(&T::operator())>>
    : public WasmHostFunc<decltype(&T::operator())> {};
 
} // namespace detail
 
using namespace detail;
 
class Func {
  friend class Val;
  friend class Instance;
  friend class Linker;
  template <typename Params, typename Results> friend class TypedFunc;
 
  wasmtime_func_t func;
 
  template <typename F>
  static wasm_trap_t *raw_callback(void *env, wasmtime_caller_t *caller,
                                   const wasmtime_val_t *args, size_t nargs,
                                   wasmtime_val_t *results, size_t nresults) {
    static_assert(alignof(Val) == alignof(wasmtime_val_t));
    static_assert(sizeof(Val) == sizeof(wasmtime_val_t));
    F *func = reinterpret_cast<F *>(env);                          // NOLINT
    Span<const Val> args_span(reinterpret_cast<const Val *>(args), // NOLINT
                              nargs);
    Span<Val> results_span(reinterpret_cast<Val *>(results), // NOLINT
                           nresults);
    Result<std::monostate, Trap> result =
        (*func)(Caller(caller), args_span, results_span);
    if (!result) {
      return result.err().ptr.release();
    }
    return nullptr;
  }
 
  template <typename F>
  static wasm_trap_t *
  raw_callback_unchecked(void *env, wasmtime_caller_t *caller,
                         wasmtime_val_raw_t *args_and_results,
                         size_t nargs_and_results) {
    using HostFunc = WasmHostFunc<F>;
    Caller cx(caller);
    F *func = reinterpret_cast<F *>(env); // NOLINT
    auto trap = HostFunc::invoke(*func, cx, args_and_results);
    if (trap) {
      return trap->ptr.release();
    }
    return nullptr;
  }
 
  template <typename F> static void raw_finalize(void *env) {
    std::unique_ptr<F> ptr(reinterpret_cast<F *>(env)); // NOLINT
  }
 
public:
  Func(wasmtime_func_t func) : func(func) {}
 
  template <typename F,
            std::enable_if_t<
                std::is_invocable_r_v<Result<std::monostate, Trap>, F, Caller,
                                      Span<const Val>, Span<Val>>,
                bool> = true>
  Func(Store::Context cx, const FuncType &ty, F f) : func({}) {
    wasmtime_func_new(cx.ptr, ty.ptr.get(), raw_callback<F>,
                      std::make_unique<F>(f).release(), raw_finalize<F>, &func);
  }
 
  template <typename F,
            std::enable_if_t<WasmHostFunc<F>::Params::valid, bool> = true,
            std::enable_if_t<WasmHostFunc<F>::Results::valid, bool> = true>
  static Func wrap(Store::Context cx, F f) {
    using HostFunc = WasmHostFunc<F>;
    auto params = HostFunc::Params::types();
    auto results = HostFunc::Results::types();
    auto ty = FuncType::from_iters(params, results);
    wasmtime_func_t func;
    wasmtime_func_new_unchecked(cx.ptr, ty.ptr.get(), raw_callback_unchecked<F>,
                                std::make_unique<F>(f).release(),
                                raw_finalize<F>, &func);
    return func;
  }
 
  template <typename I>
  TrapResult<std::vector<Val>> call(Store::Context cx, const I &begin,
                                    const I &end) const {
    std::vector<wasmtime_val_t> raw_params;
    raw_params.reserve(end - begin);
    for (auto i = begin; i != end; i++) {
      raw_params.push_back(i->val);
    }
    size_t nresults = this->type(cx)->results().size();
    std::vector<wasmtime_val_t> raw_results(nresults);
 
    wasm_trap_t *trap = nullptr;
    auto *error =
        wasmtime_func_call(cx.ptr, &func, raw_params.data(), raw_params.size(),
                           raw_results.data(), raw_results.capacity(), &trap);
    if (error != nullptr) {
      return TrapError(Error(error));
    }
    if (trap != nullptr) {
      return TrapError(Trap(trap));
    }
 
    std::vector<Val> results;
    results.reserve(nresults);
    for (size_t i = 0; i < nresults; i++) {
      results.push_back(raw_results[i]);
    }
    return results;
  }
 
  TrapResult<std::vector<Val>> call(Store::Context cx,
                                    const std::vector<Val> &params) const {
    return this->call(cx, params.begin(), params.end());
  }
 
  TrapResult<std::vector<Val>>
  call(Store::Context cx, const std::initializer_list<Val> &params) const {
    return this->call(cx, params.begin(), params.end());
  }
 
  FuncType type(Store::Context cx) const {
    return wasmtime_func_type(cx.ptr, &func);
  }
 
  template <typename Params, typename Results,
            std::enable_if_t<WasmTypeList<Params>::valid, bool> = true,
            std::enable_if_t<WasmTypeList<Results>::valid, bool> = true>
  Result<TypedFunc<Params, Results>, Trap> typed(Store::Context cx) const {
    auto ty = this->type(cx);
    if (!WasmTypeList<Params>::matches(ty->params()) ||
        !WasmTypeList<Results>::matches(ty->results())) {
      return Trap("static type for this function does not match actual type");
    }
    TypedFunc<Params, Results> ret(*this);
    return ret;
  }
 
  const wasmtime_func_t &raw_func() const { return func; }
};
 
template <typename Params, typename Results> class TypedFunc {
  friend class Func;
  Func f;
  TypedFunc(Func func) : f(func) {}
 
public:
  TrapResult<Results> call(Store::Context cx, Params params) const {
    std::array<wasmtime_val_raw_t, std::max(WasmTypeList<Params>::size,
                                            WasmTypeList<Results>::size)>
        storage;
    wasmtime_val_raw_t *ptr = storage.data();
    if (ptr == nullptr)
      ptr = reinterpret_cast<wasmtime_val_raw_t*>(alignof(wasmtime_val_raw_t));
    WasmTypeList<Params>::store(cx, ptr, params);
    wasm_trap_t *trap = nullptr;
    auto *error = wasmtime_func_call_unchecked(
        cx.raw_context(), &f.func, ptr, storage.size(), &trap);
    if (error != nullptr) {
      return TrapError(Error(error));
    }
    if (trap != nullptr) {
      return TrapError(Trap(trap));
    }
    return WasmTypeList<Results>::load(cx, ptr);
  }
 
  const Func &func() const { return f; }
};
 
inline Val::Val(std::optional<Func> func) : val{} {
  val.kind = WASMTIME_FUNCREF;
  if (func) {
    val.of.funcref = (*func).func;
  } else {
    wasmtime_funcref_set_null(&val.of.funcref);
  }
}
 
inline Val::Val(Func func) : Val(std::optional(func)) {}
inline Val::Val(ExternRef ptr) : Val(std::optional(ptr)) {}
inline Val::Val(AnyRef ptr) : Val(std::optional(ptr)) {}
 
inline std::optional<Func> Val::funcref() const {
  if (val.kind != WASMTIME_FUNCREF) {
    std::abort();
  }
  if (val.of.funcref.store_id == 0) {
    return std::nullopt;
  }
  return Func(val.of.funcref);
}
 
template <> struct detail::WasmType<std::optional<Func>> {
  static const bool valid = true;
  static const ValKind kind = ValKind::FuncRef;
  static void store(Store::Context cx, wasmtime_val_raw_t *p,
                    const std::optional<Func> func) {
    if (func) {
      p->funcref = wasmtime_func_to_raw(cx.raw_context(), &func->raw_func());
    } else {
      p->funcref = 0;
    }
  }
  static std::optional<Func> load(Store::Context cx, wasmtime_val_raw_t *p) {
    if (p->funcref == 0) {
      return std::nullopt;
    }
    wasmtime_func_t ret;
    wasmtime_func_from_raw(cx.raw_context(), p->funcref, &ret);
    return ret;
  }
};
 
class Global {
  friend class Instance;
  wasmtime_global_t global;
 
public:
  Global(wasmtime_global_t global) : global(global) {}
 
  static Result<Global> create(Store::Context cx, const GlobalType &ty,
                               const Val &init) {
    wasmtime_global_t global;
    auto *error = wasmtime_global_new(cx.ptr, ty.ptr.get(), &init.val, &global);
    if (error != nullptr) {
      return Error(error);
    }
    return Global(global);
  }
 
  GlobalType type(Store::Context cx) const {
    return wasmtime_global_type(cx.ptr, &global);
  }
 
  Val get(Store::Context cx) const;
 
  Result<std::monostate> set(Store::Context cx, const Val &val) const {
    auto *error = wasmtime_global_set(cx.ptr, &global, &val.val);
    if (error != nullptr) {
      return Error(error);
    }
    return std::monostate();
  }
};
 
class Table {
  friend class Instance;
  wasmtime_table_t table;
 
public:
  Table(wasmtime_table_t table) : table(table) {}
 
  static Result<Table> create(Store::Context cx, const TableType &ty,
                              const Val &init) {
    wasmtime_table_t table;
    auto *error = wasmtime_table_new(cx.ptr, ty.ptr.get(), &init.val, &table);
    if (error != nullptr) {
      return Error(error);
    }
    return Table(table);
  }
 
  TableType type(Store::Context cx) const {
    return wasmtime_table_type(cx.ptr, &table);
  }
 
  uint64_t size(Store::Context cx) const {
    return wasmtime_table_size(cx.ptr, &table);
  }
 
  std::optional<Val> get(Store::Context cx, uint64_t idx) const {
    Val val;
    if (wasmtime_table_get(cx.ptr, &table, idx, &val.val)) {
      return val;
    }
    return std::nullopt;
  }
 
  Result<std::monostate> set(Store::Context cx, uint64_t idx,
                             const Val &val) const {
    auto *error = wasmtime_table_set(cx.ptr, &table, idx, &val.val);
    if (error != nullptr) {
      return Error(error);
    }
    return std::monostate();
  }
 
  Result<uint64_t> grow(Store::Context cx, uint64_t delta,
                        const Val &init) const {
    uint64_t prev = 0;
    auto *error = wasmtime_table_grow(cx.ptr, &table, delta, &init.val, &prev);
    if (error != nullptr) {
      return Error(error);
    }
    return prev;
  }
};
 
// gcc 8.3.0 seems to require that this comes after the definition of `Table`. I
// don't know why...
inline Val Global::get(Store::Context cx) const {
  Val val;
  wasmtime_global_get(cx.ptr, &global, &val.val);
  return val;
}
 
class Memory {
  friend class Instance;
  wasmtime_memory_t memory;
 
public:
  Memory(wasmtime_memory_t memory) : memory(memory) {}
 
  static Result<Memory> create(Store::Context cx, const MemoryType &ty) {
    wasmtime_memory_t memory;
    auto *error = wasmtime_memory_new(cx.ptr, ty.ptr.get(), &memory);
    if (error != nullptr) {
      return Error(error);
    }
    return Memory(memory);
  }
 
  MemoryType type(Store::Context cx) const {
    return wasmtime_memory_type(cx.ptr, &memory);
  }
 
  uint64_t size(Store::Context cx) const {
    return wasmtime_memory_size(cx.ptr, &memory);
  }
 
  Span<uint8_t> data(Store::Context cx) const {
    auto *base = wasmtime_memory_data(cx.ptr, &memory);
    auto size = wasmtime_memory_data_size(cx.ptr, &memory);
    return {base, size};
  }
 
  Result<uint64_t> grow(Store::Context cx, uint64_t delta) const {
    uint64_t prev = 0;
    auto *error = wasmtime_memory_grow(cx.ptr, &memory, delta, &prev);
    if (error != nullptr) {
      return Error(error);
    }
    return prev;
  }
};
 
class Instance {
  friend class Linker;
  friend class Caller;
 
  wasmtime_instance_t instance;
 
  static Extern cvt(wasmtime_extern_t &e) {
    switch (e.kind) {
    case WASMTIME_EXTERN_FUNC:
      return Func(e.of.func);
    case WASMTIME_EXTERN_GLOBAL:
      return Global(e.of.global);
    case WASMTIME_EXTERN_MEMORY:
      return Memory(e.of.memory);
    case WASMTIME_EXTERN_TABLE:
      return Table(e.of.table);
    }
    std::abort();
  }
 
  static void cvt(const Extern &e, wasmtime_extern_t &raw) {
    if (const auto *func = std::get_if<Func>(&e)) {
      raw.kind = WASMTIME_EXTERN_FUNC;
      raw.of.func = func->func;
    } else if (const auto *global = std::get_if<Global>(&e)) {
      raw.kind = WASMTIME_EXTERN_GLOBAL;
      raw.of.global = global->global;
    } else if (const auto *table = std::get_if<Table>(&e)) {
      raw.kind = WASMTIME_EXTERN_TABLE;
      raw.of.table = table->table;
    } else if (const auto *memory = std::get_if<Memory>(&e)) {
      raw.kind = WASMTIME_EXTERN_MEMORY;
      raw.of.memory = memory->memory;
    } else {
      std::abort();
    }
  }
 
public:
  Instance(wasmtime_instance_t instance) : instance(instance) {}
 
  static TrapResult<Instance> create(Store::Context cx, const Module &m,
                                     const std::vector<Extern> &imports) {
    std::vector<wasmtime_extern_t> raw_imports;
    for (const auto &item : imports) {
      raw_imports.push_back(wasmtime_extern_t{});
      auto &last = raw_imports.back();
      Instance::cvt(item, last);
    }
    wasmtime_instance_t instance;
    wasm_trap_t *trap = nullptr;
    auto *error = wasmtime_instance_new(cx.ptr, m.ptr.get(), raw_imports.data(),
                                        raw_imports.size(), &instance, &trap);
    if (error != nullptr) {
      return TrapError(Error(error));
    }
    if (trap != nullptr) {
      return TrapError(Trap(trap));
    }
    return Instance(instance);
  }
 
  std::optional<Extern> get(Store::Context cx, std::string_view name) {
    wasmtime_extern_t e;
    if (!wasmtime_instance_export_get(cx.ptr, &instance, name.data(),
                                      name.size(), &e)) {
      return std::nullopt;
    }
    return Instance::cvt(e);
  }
 
  std::optional<std::pair<std::string_view, Extern>> get(Store::Context cx,
                                                         size_t idx) {
    wasmtime_extern_t e;
    // I'm not sure why clang-tidy thinks this is using va_list or anything
    // related to that...
    // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg)
    char *name = nullptr;
    size_t len = 0;
    if (!wasmtime_instance_export_nth(cx.ptr, &instance, idx, &name, &len,
                                      &e)) {
      return std::nullopt;
    }
    std::string_view n(name, len);
    return std::pair(n, Instance::cvt(e));
  }
};
 
inline std::optional<Extern> Caller::get_export(std::string_view name) {
  wasmtime_extern_t item;
  if (wasmtime_caller_export_get(ptr, name.data(), name.size(), &item)) {
    return Instance::cvt(item);
  }
  return std::nullopt;
}
 
class Linker {
  struct deleter {
    void operator()(wasmtime_linker_t *p) const { wasmtime_linker_delete(p); }
  };
 
  std::unique_ptr<wasmtime_linker_t, deleter> ptr;
 
public:
  explicit Linker(Engine &engine)
      : ptr(wasmtime_linker_new(engine.ptr.get())) {}
 
  void allow_shadowing(bool allow) {
    wasmtime_linker_allow_shadowing(ptr.get(), allow);
  }
 
  Result<std::monostate> define(Store::Context cx, std::string_view module,
                                std::string_view name, const Extern &item) {
    wasmtime_extern_t raw;
    Instance::cvt(item, raw);
    auto *error =
        wasmtime_linker_define(ptr.get(), cx.ptr, module.data(), module.size(),
                               name.data(), name.size(), &raw);
    if (error != nullptr) {
      return Error(error);
    }
    return std::monostate();
  }
 
  Result<std::monostate> define_wasi() {
    auto *error = wasmtime_linker_define_wasi(ptr.get());
    if (error != nullptr) {
      return Error(error);
    }
    return std::monostate();
  }
 
  Result<std::monostate>
  define_instance(Store::Context cx, std::string_view name, Instance instance) {
    auto *error = wasmtime_linker_define_instance(
        ptr.get(), cx.ptr, name.data(), name.size(), &instance.instance);
    if (error != nullptr) {
      return Error(error);
    }
    return std::monostate();
  }
 
  TrapResult<Instance> instantiate(Store::Context cx, const Module &m) {
    wasmtime_instance_t instance;
    wasm_trap_t *trap = nullptr;
    auto *error = wasmtime_linker_instantiate(ptr.get(), cx.ptr, m.ptr.get(),
                                              &instance, &trap);
    if (error != nullptr) {
      return TrapError(Error(error));
    }
    if (trap != nullptr) {
      return TrapError(Trap(trap));
    }
    return Instance(instance);
  }
 
  Result<std::monostate> module(Store::Context cx, std::string_view name,
                                const Module &m) {
    auto *error = wasmtime_linker_module(ptr.get(), cx.ptr, name.data(),
                                         name.size(), m.ptr.get());
    if (error != nullptr) {
      return Error(error);
    }
    return std::monostate();
  }
 
  [[nodiscard]] std::optional<Extern>
  get(Store::Context cx, std::string_view module, std::string_view name) {
    wasmtime_extern_t item;
    if (wasmtime_linker_get(ptr.get(), cx.ptr, module.data(), module.size(),
                            name.data(), name.size(), &item)) {
      return Instance::cvt(item);
    }
    return std::nullopt;
  }
 
  template <typename F,
            std::enable_if_t<
                std::is_invocable_r_v<Result<std::monostate, Trap>, F, Caller,
                                      Span<const Val>, Span<Val>>,
                bool> = true>
  Result<std::monostate> func_new(std::string_view module,
                                  std::string_view name, const FuncType &ty,
                                  F&& f) {
 
    auto *error = wasmtime_linker_define_func(
        ptr.get(), module.data(), module.length(), name.data(), name.length(),
        ty.ptr.get(), Func::raw_callback<std::remove_reference_t<F>>, std::make_unique<std::remove_reference_t<F>>(std::forward<F>(f)).release(),
        Func::raw_finalize<std::remove_reference_t<F>>);
 
    if (error != nullptr) {
      return Error(error);
    }
 
    return std::monostate();
  }
 
  template <typename F,
            std::enable_if_t<WasmHostFunc<F>::Params::valid, bool> = true,
            std::enable_if_t<WasmHostFunc<F>::Results::valid, bool> = true>
  Result<std::monostate> func_wrap(std::string_view module,
                                   std::string_view name, F&& f) {
    using HostFunc = WasmHostFunc<F>;
    auto params = HostFunc::Params::types();
    auto results = HostFunc::Results::types();
    auto ty = FuncType::from_iters(params, results);
    auto *error = wasmtime_linker_define_func_unchecked(
        ptr.get(), module.data(), module.length(), name.data(), name.length(),
        ty.ptr.get(), Func::raw_callback_unchecked<std::remove_reference_t<F>>,
        std::make_unique<std::remove_reference_t<F>>(std::forward<F>(f)).release(), Func::raw_finalize<std::remove_reference_t<F>>);
 
    if (error != nullptr) {
      return Error(error);
    }
 
    return std::monostate();
  }
 
  Result<Func> get_default(Store::Context cx, std::string_view name) {
    wasmtime_func_t item;
    auto *error = wasmtime_linker_get_default(ptr.get(), cx.ptr, name.data(),
                                              name.size(), &item);
    if (error != nullptr) {
      return Error(error);
    }
    return Func(item);
  }
};
 
} // namespace wasmtime
 
#endif // WASMTIME_HH