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// Copyright 2023 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Definitions for template helpers to wrap C++ functions as CEL extension
// function implementations.
// TODO(issues/5): Add generalized version in addition to the common cases
// of unary/binary functions.
#ifndef THIRD_PARTY_CEL_CPP_BASE_FUNCTION_ADAPTER_H_
#define THIRD_PARTY_CEL_CPP_BASE_FUNCTION_ADAPTER_H_
#include <functional>
#include <memory>
#include "absl/log/die_if_null.h"
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/strings/string_view.h"
#include "absl/types/span.h"
#include "base/function.h"
#include "base/function_descriptor.h"
#include "base/handle.h"
#include "base/internal/function_adapter.h"
#include "base/value.h"
#include "internal/status_macros.h"
namespace cel {
namespace internal {
template <typename T>
struct AdaptedTypeTraits {
using AssignableType = T;
static T ToArg(AssignableType v) { return v; }
};
// Specialization for cref parameters without forcing a temporary copy of the
// underlying handle argument.
template <typename T>
struct AdaptedTypeTraits<const T&> {
using AssignableType = const T*;
static const T& ToArg(AssignableType v) { return *ABSL_DIE_IF_NULL(v); }
};
} // namespace internal
// Adapter class for generating CEL extension functions from a two argument
// function. Generates an implementation of the cel::Function interface that
// calls the function to wrap.
//
// Extension functions must distinguish between recoverable errors (error that
// should participate in CEL's error pruning) and unrecoverable errors (a non-ok
// absl::Status that stops evaluation). The function to wrap may return
// StatusOr<T> to propagate a Status, or return a Handle<Value> with an Error
// value to introduce a CEL error.
//
// To introduce an extension function that may accept any kind of CEL value as
// an argument, the wrapped function should use a Value<Handle> parameter and
// check the type of the argument at evaluation time.
//
// Supported CEL to C++ type mappings:
// bool -> bool
// double -> double
// uint -> uint64_t
// int -> int64_t
// timestamp -> absl::Time
// duration -> absl::Duration
//
// Complex types may be referred to by cref or handle.
// To return these, users should return a Handle<Value>.
// any/dyn -> Handle<Value>, const Value&
// string -> Handle<StringValue> | const StringValue&
// bytes -> Handle<BytesValue> | const BytesValue&
// list -> Handle<ListValue> | const ListValue&
// map -> Handle<MapValue> | const MapValue&
// struct -> Handle<StructValue> | const StructValue&
// null -> Handle<NullValue> | const NullValue&
//
// To intercept error and unknown arguments, users must use a non-strict
// overload with all arguments typed as any and check the kind of the
// Handle<Value> argument.
//
// Example Usage:
// double SquareDifference(ValueFactory&, double x, double y) {
// return x * x - y * y;
// }
//
// {
// std::unique_ptr<CelExpressionBuilder> builder;
// // Initialize Expression builder with built-ins as needed.
//
// CEL_RETURN_IF_ERROR(
// builder->GetRegistry()->Register(
// UnaryFunctionAdapter<double, double, double>::CreateDescriptor(
// "sq_diff", /*receiver_style=*/false),
// BinaryFunctionAdapter<double, double, double>::WrapFunction(
// &SquareDifference)));
// }
//
// example CEL expression:
// sq_diff(4, 3) == 7 [true]
//
template <typename T, typename U, typename V>
class BinaryFunctionAdapter {
public:
using FunctionType = std::function<T(ValueFactory&, U, V)>;
static std::unique_ptr<cel::Function> WrapFunction(FunctionType fn) {
return std::make_unique<BinaryFunctionImpl>(std::move(fn));
}
static FunctionDescriptor CreateDescriptor(absl::string_view name,
bool receiver_style,
bool is_strict = true) {
return FunctionDescriptor(
name, receiver_style,
{internal::AdaptedKind<U>(), internal::AdaptedKind<V>()}, is_strict);
}
private:
class BinaryFunctionImpl : public cel::Function {
public:
explicit BinaryFunctionImpl(FunctionType fn) : fn_(std::move(fn)) {}
absl::StatusOr<Handle<Value>> Invoke(
const FunctionEvaluationContext& context,
absl::Span<const Handle<Value>> args) const override {
using Arg1Traits = internal::AdaptedTypeTraits<U>;
using Arg2Traits = internal::AdaptedTypeTraits<V>;
if (args.size() != 2) {
return absl::InvalidArgumentError(
"unexpected number of arguments for binary function");
}
typename Arg1Traits::AssignableType arg1;
typename Arg2Traits::AssignableType arg2;
CEL_RETURN_IF_ERROR(internal::HandleToAdaptedVisitor{args[0]}(&arg1));
CEL_RETURN_IF_ERROR(internal::HandleToAdaptedVisitor{args[1]}(&arg2));
T result = fn_(context.value_factory(), Arg1Traits::ToArg(arg1),
Arg2Traits::ToArg(arg2));
return internal::AdaptedToHandleVisitor{context.value_factory()}(
std::move(result));
}
private:
BinaryFunctionAdapter::FunctionType fn_;
};
};
// Adapter class for generating CEL extension functions from a one argument
// function.
//
// See documentation for Binary Function adapter for general recommendations.
//
// Example Usage:
// double Invert(ValueFactory&, double x) {
// return 1 / x;
// }
//
// {
// std::unique_ptr<CelExpressionBuilder> builder;
//
// CEL_RETURN_IF_ERROR(
// builder->GetRegistry()->Register(
// UnaryFunctionAdapter<double, double>::CreateDescriptor("inv",
// /*receiver_style=*/false),
// UnaryFunctionAdapter<double, double>::WrapFunction(&Invert)));
// }
// // example CEL expression
// inv(4) == 1/4 [true]
template <typename T, typename U>
class UnaryFunctionAdapter {
public:
using FunctionType = std::function<T(ValueFactory&, U)>;
static std::unique_ptr<cel::Function> WrapFunction(FunctionType fn) {
return std::make_unique<UnaryFunctionImpl>(std::move(fn));
}
static FunctionDescriptor CreateDescriptor(absl::string_view name,
bool receiver_style,
bool is_strict = true) {
return FunctionDescriptor(name, receiver_style,
{internal::AdaptedKind<U>()}, is_strict);
}
private:
class UnaryFunctionImpl : public cel::Function {
public:
explicit UnaryFunctionImpl(FunctionType fn) : fn_(std::move(fn)) {}
absl::StatusOr<Handle<Value>> Invoke(
const FunctionEvaluationContext& context,
absl::Span<const Handle<Value>> args) const override {
using ArgTraits = internal::AdaptedTypeTraits<U>;
if (args.size() != 1) {
return absl::InvalidArgumentError(
"unexpected number of arguments for unary function");
}
typename ArgTraits::AssignableType arg1;
CEL_RETURN_IF_ERROR(internal::HandleToAdaptedVisitor{args[0]}(&arg1));
T result = fn_(context.value_factory(), ArgTraits::ToArg(arg1));
return internal::AdaptedToHandleVisitor{context.value_factory()}(
std::move(result));
}
private:
FunctionType fn_;
};
};
} // namespace cel
#endif // THIRD_PARTY_CEL_CPP_BASE_FUNCTION_ADAPTER_H_