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// Copyright 2019 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
//
// http://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.
package cel
import (
"fmt"
"google.golang.org/protobuf/proto"
"google.golang.org/protobuf/reflect/protodesc"
"google.golang.org/protobuf/reflect/protoreflect"
"google.golang.org/protobuf/reflect/protoregistry"
"google.golang.org/protobuf/types/dynamicpb"
"github.com/google/cel-go/checker"
"github.com/google/cel-go/common/containers"
"github.com/google/cel-go/common/functions"
"github.com/google/cel-go/common/types"
"github.com/google/cel-go/common/types/pb"
"github.com/google/cel-go/common/types/ref"
"github.com/google/cel-go/interpreter"
"github.com/google/cel-go/parser"
exprpb "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
descpb "google.golang.org/protobuf/types/descriptorpb"
)
// These constants beginning with "Feature" enable optional behavior in
// the library. See the documentation for each constant to see its
// effects, compatibility restrictions, and standard conformance.
const (
_ = iota
// Enable the tracking of function call expressions replaced by macros.
featureEnableMacroCallTracking
// Enable the use of cross-type numeric comparisons at the type-checker.
featureCrossTypeNumericComparisons
// Enable eager validation of declarations to ensure that Env values created
// with `Extend` inherit a validated list of declarations from the parent Env.
featureEagerlyValidateDeclarations
// Enable the use of the default UTC timezone when a timezone is not specified
// on a CEL timestamp operation. This fixes the scenario where the input time
// is not already in UTC.
featureDefaultUTCTimeZone
// Enable the serialization of logical operator ASTs as variadic calls, thus
// compressing the logic graph to a single call when multiple like-operator
// expressions occur: e.g. a && b && c && d -> call(_&&_, [a, b, c, d])
featureVariadicLogicalASTs
)
// EnvOption is a functional interface for configuring the environment.
type EnvOption func(e *Env) (*Env, error)
// ClearMacros options clears all parser macros.
//
// Clearing macros will ensure CEL expressions can only contain linear evaluation paths, as
// comprehensions such as `all` and `exists` are enabled only via macros.
func ClearMacros() EnvOption {
return func(e *Env) (*Env, error) {
e.macros = NoMacros
return e, nil
}
}
// CustomTypeAdapter swaps the default types.Adapter implementation with a custom one.
//
// Note: This option must be specified before the Types and TypeDescs options when used together.
func CustomTypeAdapter(adapter types.Adapter) EnvOption {
return func(e *Env) (*Env, error) {
e.adapter = adapter
return e, nil
}
}
// CustomTypeProvider replaces the types.Provider implementation with a custom one.
//
// The `provider` variable type may either be types.Provider or ref.TypeProvider (deprecated)
//
// Note: This option must be specified before the Types and TypeDescs options when used together.
func CustomTypeProvider(provider any) EnvOption {
return func(e *Env) (*Env, error) {
var err error
e.provider, err = maybeInteropProvider(provider)
return e, err
}
}
// Declarations option extends the declaration set configured in the environment.
//
// Note: Declarations will by default be appended to the pre-existing declaration set configured
// for the environment. The NewEnv call builds on top of the standard CEL declarations. For a
// purely custom set of declarations use NewCustomEnv.
func Declarations(decls ...*exprpb.Decl) EnvOption {
declOpts := []EnvOption{}
var err error
var opt EnvOption
// Convert the declarations to `EnvOption` values ahead of time.
// Surface any errors in conversion when the options are applied.
for _, d := range decls {
opt, err = ExprDeclToDeclaration(d)
if err != nil {
break
}
declOpts = append(declOpts, opt)
}
return func(e *Env) (*Env, error) {
if err != nil {
return nil, err
}
for _, o := range declOpts {
e, err = o(e)
if err != nil {
return nil, err
}
}
return e, nil
}
}
// EagerlyValidateDeclarations ensures that any collisions between configured declarations are caught
// at the time of the `NewEnv` call.
//
// Eagerly validating declarations is also useful for bootstrapping a base `cel.Env` value.
// Calls to base `Env.Extend()` will be significantly faster when declarations are eagerly validated
// as declarations will be collision-checked at most once and only incrementally by way of `Extend`
//
// Disabled by default as not all environments are used for type-checking.
func EagerlyValidateDeclarations(enabled bool) EnvOption {
return features(featureEagerlyValidateDeclarations, enabled)
}
// HomogeneousAggregateLiterals disables mixed type list and map literal values.
//
// Note, it is still possible to have heterogeneous aggregates when provided as variables to the
// expression, as well as via conversion of well-known dynamic types, or with unchecked
// expressions.
func HomogeneousAggregateLiterals() EnvOption {
return ASTValidators(ValidateHomogeneousAggregateLiterals())
}
// variadicLogicalOperatorASTs flatten like-operator chained logical expressions into a single
// variadic call with N-terms. This behavior is useful when serializing to a protocol buffer as
// it will reduce the number of recursive calls needed to deserialize the AST later.
//
// For example, given the following expression the call graph will be rendered accordingly:
//
// expression: a && b && c && (d || e)
// ast: call(_&&_, [a, b, c, call(_||_, [d, e])])
func variadicLogicalOperatorASTs() EnvOption {
return features(featureVariadicLogicalASTs, true)
}
// Macros option extends the macro set configured in the environment.
//
// Note: This option must be specified after ClearMacros if used together.
func Macros(macros ...Macro) EnvOption {
return func(e *Env) (*Env, error) {
e.macros = append(e.macros, macros...)
return e, nil
}
}
// Container sets the container for resolving variable names. Defaults to an empty container.
//
// If all references within an expression are relative to a protocol buffer package, then
// specifying a container of `google.type` would make it possible to write expressions such as
// `Expr{expression: 'a < b'}` instead of having to write `google.type.Expr{...}`.
func Container(name string) EnvOption {
return func(e *Env) (*Env, error) {
cont, err := e.Container.Extend(containers.Name(name))
if err != nil {
return nil, err
}
e.Container = cont
return e, nil
}
}
// Abbrevs configures a set of simple names as abbreviations for fully-qualified names.
//
// An abbreviation (abbrev for short) is a simple name that expands to a fully-qualified name.
// Abbreviations can be useful when working with variables, functions, and especially types from
// multiple namespaces:
//
// // CEL object construction
// qual.pkg.version.ObjTypeName{
// field: alt.container.ver.FieldTypeName{value: ...}
// }
//
// Only one the qualified names above may be used as the CEL container, so at least one of these
// references must be a long qualified name within an otherwise short CEL program. Using the
// following abbreviations, the program becomes much simpler:
//
// // CEL Go option
// Abbrevs("qual.pkg.version.ObjTypeName", "alt.container.ver.FieldTypeName")
// // Simplified Object construction
// ObjTypeName{field: FieldTypeName{value: ...}}
//
// There are a few rules for the qualified names and the simple abbreviations generated from them:
// - Qualified names must be dot-delimited, e.g. `package.subpkg.name`.
// - The last element in the qualified name is the abbreviation.
// - Abbreviations must not collide with each other.
// - The abbreviation must not collide with unqualified names in use.
//
// Abbreviations are distinct from container-based references in the following important ways:
// - Abbreviations must expand to a fully-qualified name.
// - Expanded abbreviations do not participate in namespace resolution.
// - Abbreviation expansion is done instead of the container search for a matching identifier.
// - Containers follow C++ namespace resolution rules with searches from the most qualified name
//
// to the least qualified name.
//
// - Container references within the CEL program may be relative, and are resolved to fully
//
// qualified names at either type-check time or program plan time, whichever comes first.
//
// If there is ever a case where an identifier could be in both the container and as an
// abbreviation, the abbreviation wins as this will ensure that the meaning of a program is
// preserved between compilations even as the container evolves.
func Abbrevs(qualifiedNames ...string) EnvOption {
return func(e *Env) (*Env, error) {
cont, err := e.Container.Extend(containers.Abbrevs(qualifiedNames...))
if err != nil {
return nil, err
}
e.Container = cont
return e, nil
}
}
// Types adds one or more type declarations to the environment, allowing for construction of
// type-literals whose definitions are included in the common expression built-in set.
//
// The input types may either be instances of `proto.Message` or `ref.Type`. Any other type
// provided to this option will result in an error.
//
// Well-known protobuf types within the `google.protobuf.*` package are included in the standard
// environment by default.
//
// Note: This option must be specified after the CustomTypeProvider option when used together.
func Types(addTypes ...any) EnvOption {
return func(e *Env) (*Env, error) {
var reg ref.TypeRegistry
var isReg bool
reg, isReg = e.provider.(*types.Registry)
if !isReg {
reg, isReg = e.provider.(ref.TypeRegistry)
}
if !isReg {
return nil, fmt.Errorf("custom types not supported by provider: %T", e.provider)
}
for _, t := range addTypes {
switch v := t.(type) {
case proto.Message:
fdMap := pb.CollectFileDescriptorSet(v)
for _, fd := range fdMap {
err := reg.RegisterDescriptor(fd)
if err != nil {
return nil, err
}
}
case ref.Type:
err := reg.RegisterType(v)
if err != nil {
return nil, err
}
default:
return nil, fmt.Errorf("unsupported type: %T", t)
}
}
return e, nil
}
}
// TypeDescs adds type declarations from any protoreflect.FileDescriptor, protoregistry.Files,
// google.protobuf.FileDescriptorProto or google.protobuf.FileDescriptorSet provided.
//
// Note that messages instantiated from these descriptors will be *dynamicpb.Message values
// rather than the concrete message type.
//
// TypeDescs are hermetic to a single Env object, but may be copied to other Env values via
// extension or by re-using the same EnvOption with another NewEnv() call.
func TypeDescs(descs ...any) EnvOption {
return func(e *Env) (*Env, error) {
reg, isReg := e.provider.(ref.TypeRegistry)
if !isReg {
return nil, fmt.Errorf("custom types not supported by provider: %T", e.provider)
}
// Scan the input descriptors for FileDescriptorProto messages and accumulate them into a
// synthetic FileDescriptorSet as the FileDescriptorProto messages may refer to each other
// and will not resolve properly unless they are part of the same set.
var fds *descpb.FileDescriptorSet
for _, d := range descs {
switch f := d.(type) {
case *descpb.FileDescriptorProto:
if fds == nil {
fds = &descpb.FileDescriptorSet{
File: []*descpb.FileDescriptorProto{},
}
}
fds.File = append(fds.File, f)
}
}
if fds != nil {
if err := registerFileSet(reg, fds); err != nil {
return nil, err
}
}
for _, d := range descs {
switch f := d.(type) {
case *protoregistry.Files:
if err := registerFiles(reg, f); err != nil {
return nil, err
}
case protoreflect.FileDescriptor:
if err := reg.RegisterDescriptor(f); err != nil {
return nil, err
}
case *descpb.FileDescriptorSet:
if err := registerFileSet(reg, f); err != nil {
return nil, err
}
case *descpb.FileDescriptorProto:
// skip, handled as a synthetic file descriptor set.
default:
return nil, fmt.Errorf("unsupported type descriptor: %T", d)
}
}
return e, nil
}
}
func registerFileSet(reg ref.TypeRegistry, fileSet *descpb.FileDescriptorSet) error {
files, err := protodesc.NewFiles(fileSet)
if err != nil {
return fmt.Errorf("protodesc.NewFiles(%v) failed: %v", fileSet, err)
}
return registerFiles(reg, files)
}
func registerFiles(reg ref.TypeRegistry, files *protoregistry.Files) error {
var err error
files.RangeFiles(func(fd protoreflect.FileDescriptor) bool {
err = reg.RegisterDescriptor(fd)
return err == nil
})
return err
}
// ProgramOption is a functional interface for configuring evaluation bindings and behaviors.
type ProgramOption func(p *prog) (*prog, error)
// CustomDecorator appends an InterpreterDecorator to the program.
//
// InterpretableDecorators can be used to inspect, alter, or replace the Program plan.
func CustomDecorator(dec interpreter.InterpretableDecorator) ProgramOption {
return func(p *prog) (*prog, error) {
p.decorators = append(p.decorators, dec)
return p, nil
}
}
// Functions adds function overloads that extend or override the set of CEL built-ins.
//
// Deprecated: use Function() instead to declare the function, its overload signatures,
// and the overload implementations.
func Functions(funcs ...*functions.Overload) ProgramOption {
return func(p *prog) (*prog, error) {
if err := p.dispatcher.Add(funcs...); err != nil {
return nil, err
}
return p, nil
}
}
// Globals sets the global variable values for a given program. These values may be shadowed by
// variables with the same name provided to the Eval() call. If Globals is used in a Library with
// a Lib EnvOption, vars may shadow variables provided by previously added libraries.
//
// The vars value may either be an `interpreter.Activation` instance or a `map[string]any`.
func Globals(vars any) ProgramOption {
return func(p *prog) (*prog, error) {
defaultVars, err := interpreter.NewActivation(vars)
if err != nil {
return nil, err
}
if p.defaultVars != nil {
defaultVars = interpreter.NewHierarchicalActivation(p.defaultVars, defaultVars)
}
p.defaultVars = defaultVars
return p, nil
}
}
// OptimizeRegex provides a way to replace the InterpretableCall for regex functions. This can be used
// to compile regex string constants at program creation time and report any errors and then use the
// compiled regex for all regex function invocations.
func OptimizeRegex(regexOptimizations ...*interpreter.RegexOptimization) ProgramOption {
return func(p *prog) (*prog, error) {
p.regexOptimizations = append(p.regexOptimizations, regexOptimizations...)
return p, nil
}
}
// EvalOption indicates an evaluation option that may affect the evaluation behavior or information
// in the output result.
type EvalOption int
const (
// OptTrackState will cause the runtime to return an immutable EvalState value in the Result.
OptTrackState EvalOption = 1 << iota
// OptExhaustiveEval causes the runtime to disable short-circuits and track state.
OptExhaustiveEval EvalOption = 1<<iota | OptTrackState
// OptOptimize precomputes functions and operators with constants as arguments at program
// creation time. It also pre-compiles regex pattern constants passed to 'matches', reports any compilation errors
// at program creation and uses the compiled regex pattern for all 'matches' function invocations.
// This flag is useful when the expression will be evaluated repeatedly against
// a series of different inputs.
OptOptimize EvalOption = 1 << iota
// OptPartialEval enables the evaluation of a partial state where the input data that may be
// known to be missing, either as top-level variables, or somewhere within a variable's object
// member graph.
//
// By itself, OptPartialEval does not change evaluation behavior unless the input to the
// Program Eval() call is created via PartialVars().
OptPartialEval EvalOption = 1 << iota
// OptTrackCost enables the runtime cost calculation while validation and return cost within evalDetails
// cost calculation is available via func ActualCost()
OptTrackCost EvalOption = 1 << iota
// OptCheckStringFormat enables compile-time checking of string.format calls for syntax/cardinality.
//
// Deprecated: use ext.StringsValidateFormatCalls() as this option is now a no-op.
OptCheckStringFormat EvalOption = 1 << iota
)
// EvalOptions sets one or more evaluation options which may affect the evaluation or Result.
func EvalOptions(opts ...EvalOption) ProgramOption {
return func(p *prog) (*prog, error) {
for _, opt := range opts {
p.evalOpts |= opt
}
return p, nil
}
}
// InterruptCheckFrequency configures the number of iterations within a comprehension to evaluate
// before checking whether the function evaluation has been interrupted.
func InterruptCheckFrequency(checkFrequency uint) ProgramOption {
return func(p *prog) (*prog, error) {
p.interruptCheckFrequency = checkFrequency
return p, nil
}
}
// CostEstimatorOptions configure type-check time options for estimating expression cost.
func CostEstimatorOptions(costOpts ...checker.CostOption) EnvOption {
return func(e *Env) (*Env, error) {
e.costOptions = append(e.costOptions, costOpts...)
return e, nil
}
}
// CostTrackerOptions configures a set of options for cost-tracking.
//
// Note, CostTrackerOptions is a no-op unless CostTracking is also enabled.
func CostTrackerOptions(costOpts ...interpreter.CostTrackerOption) ProgramOption {
return func(p *prog) (*prog, error) {
p.costOptions = append(p.costOptions, costOpts...)
return p, nil
}
}
// CostTracking enables cost tracking and registers a ActualCostEstimator that can optionally provide a runtime cost estimate for any function calls.
func CostTracking(costEstimator interpreter.ActualCostEstimator) ProgramOption {
return func(p *prog) (*prog, error) {
p.callCostEstimator = costEstimator
p.evalOpts |= OptTrackCost
return p, nil
}
}
// CostLimit enables cost tracking and sets configures program evaluation to exit early with a
// "runtime cost limit exceeded" error if the runtime cost exceeds the costLimit.
// The CostLimit is a metric that corresponds to the number and estimated expense of operations
// performed while evaluating an expression. It is indicative of CPU usage, not memory usage.
func CostLimit(costLimit uint64) ProgramOption {
return func(p *prog) (*prog, error) {
p.costLimit = &costLimit
p.evalOpts |= OptTrackCost
return p, nil
}
}
func fieldToCELType(field protoreflect.FieldDescriptor) (*Type, error) {
if field.Kind() == protoreflect.MessageKind || field.Kind() == protoreflect.GroupKind {
msgName := (string)(field.Message().FullName())
return ObjectType(msgName), nil
}
if primitiveType, found := types.ProtoCELPrimitives[field.Kind()]; found {
return primitiveType, nil
}
if field.Kind() == protoreflect.EnumKind {
return IntType, nil
}
return nil, fmt.Errorf("field %s type %s not implemented", field.FullName(), field.Kind().String())
}
func fieldToVariable(field protoreflect.FieldDescriptor) (EnvOption, error) {
name := string(field.Name())
if field.IsMap() {
mapKey := field.MapKey()
mapValue := field.MapValue()
keyType, err := fieldToCELType(mapKey)
if err != nil {
return nil, err
}
valueType, err := fieldToCELType(mapValue)
if err != nil {
return nil, err
}
return Variable(name, MapType(keyType, valueType)), nil
}
if field.IsList() {
elemType, err := fieldToCELType(field)
if err != nil {
return nil, err
}
return Variable(name, ListType(elemType)), nil
}
celType, err := fieldToCELType(field)
if err != nil {
return nil, err
}
return Variable(name, celType), nil
}
// DeclareContextProto returns an option to extend CEL environment with declarations from the given context proto.
// Each field of the proto defines a variable of the same name in the environment.
// https://github.com/google/cel-spec/blob/master/doc/langdef.md#evaluation-environment
func DeclareContextProto(descriptor protoreflect.MessageDescriptor) EnvOption {
return func(e *Env) (*Env, error) {
fields := descriptor.Fields()
for i := 0; i < fields.Len(); i++ {
field := fields.Get(i)
variable, err := fieldToVariable(field)
if err != nil {
return nil, err
}
e, err = variable(e)
if err != nil {
return nil, err
}
}
return Types(dynamicpb.NewMessage(descriptor))(e)
}
}
// ContextProtoVars uses the fields of the input proto.Messages as top-level variables within an Activation.
//
// Consider using with `DeclareContextProto` to simplify variable type declarations and publishing when using
// protocol buffers.
func ContextProtoVars(ctx proto.Message) (interpreter.Activation, error) {
if ctx == nil || !ctx.ProtoReflect().IsValid() {
return interpreter.EmptyActivation(), nil
}
reg, err := types.NewRegistry(ctx)
if err != nil {
return nil, err
}
pbRef := ctx.ProtoReflect()
typeName := string(pbRef.Descriptor().FullName())
fields := pbRef.Descriptor().Fields()
vars := make(map[string]any, fields.Len())
for i := 0; i < fields.Len(); i++ {
field := fields.Get(i)
sft, found := reg.FindStructFieldType(typeName, field.TextName())
if !found {
return nil, fmt.Errorf("no such field: %s", field.TextName())
}
fieldVal, err := sft.GetFrom(ctx)
if err != nil {
return nil, err
}
vars[field.TextName()] = fieldVal
}
return interpreter.NewActivation(vars)
}
// EnableMacroCallTracking ensures that call expressions which are replaced by macros
// are tracked in the `SourceInfo` of parsed and checked expressions.
func EnableMacroCallTracking() EnvOption {
return features(featureEnableMacroCallTracking, true)
}
// CrossTypeNumericComparisons makes it possible to compare across numeric types, e.g. double < int
func CrossTypeNumericComparisons(enabled bool) EnvOption {
return features(featureCrossTypeNumericComparisons, enabled)
}
// DefaultUTCTimeZone ensures that time-based operations use the UTC timezone rather than the
// input time's local timezone.
func DefaultUTCTimeZone(enabled bool) EnvOption {
return features(featureDefaultUTCTimeZone, enabled)
}
// features sets the given feature flags. See list of Feature constants above.
func features(flag int, enabled bool) EnvOption {
return func(e *Env) (*Env, error) {
e.features[flag] = enabled
return e, nil
}
}
// ParserRecursionLimit adjusts the AST depth the parser will tolerate.
// Defaults defined in the parser package.
func ParserRecursionLimit(limit int) EnvOption {
return func(e *Env) (*Env, error) {
e.prsrOpts = append(e.prsrOpts, parser.MaxRecursionDepth(limit))
return e, nil
}
}
// ParserExpressionSizeLimit adjusts the number of code points the expression parser is allowed to parse.
// Defaults defined in the parser package.
func ParserExpressionSizeLimit(limit int) EnvOption {
return func(e *Env) (*Env, error) {
e.prsrOpts = append(e.prsrOpts, parser.ExpressionSizeCodePointLimit(limit))
return e, nil
}
}
func maybeInteropProvider(provider any) (types.Provider, error) {
switch p := provider.(type) {
case types.Provider:
return p, nil
case ref.TypeProvider:
return &interopCELTypeProvider{TypeProvider: p}, nil
default:
return nil, fmt.Errorf("unsupported type provider: %T", provider)
}
}
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