cel

package
v0.15.0 Latest Latest
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 Go to latest Published: May 2, 2023 License: Apache-2.0, BSD-3-Clause Imports: 29 Imported by: 481

Documentation

Overview

Package cel defines the top-level interface for the Common Expression Language (CEL).

CEL is a non-Turing complete expression language designed to parse, check, and evaluate expressions against user-defined environments.

Example 
package main

import (
	"fmt"
	"log"

	"github.com/google/cel-go/cel"
	"github.com/google/cel-go/common/types"
	"github.com/google/cel-go/common/types/ref"
)

func main() {
	// Create the CEL environment with declarations for the input attributes and the extension functions.
	// In many cases the desired functionality will be present in a built-in function.
	e, err := cel.NewEnv(
		// Variable identifiers used within this expression.
		cel.Variable("i", cel.StringType),
		cel.Variable("you", cel.StringType),
		// Function to generate a greeting from one person to another: i.greet(you)
		cel.Function("greet",
			cel.MemberOverload("string_greet_string", []*cel.Type{cel.StringType, cel.StringType}, cel.StringType,
				cel.BinaryBinding(func(lhs, rhs ref.Val) ref.Val {
					return types.String(fmt.Sprintf("Hello %s! Nice to meet you, I'm %s.\n", rhs, lhs))
				}),
			),
		),
	)
	if err != nil {
		log.Fatalf("environment creation error: %s\n", err)
	}

	// Compile the expression.
	ast, iss := e.Compile("i.greet(you)")
	if iss.Err() != nil {
		log.Fatalln(iss.Err())
	}

	// Create the program.
	prg, err := e.Program(ast)
	if err != nil {
		log.Fatalf("program creation error: %s\n", err)
	}

	// Evaluate the program against some inputs. Note: the details return is not used.
	out, _, err := prg.Eval(map[string]any{
		// Native values are converted to CEL values under the covers.
		"i": "CEL",
		// Values may also be lazily supplied.
		"you": func() ref.Val { return types.String("world") },
	})
	if err != nil {
		log.Fatalf("runtime error: %s\n", err)
	}

	fmt.Println(out)
}

Output:

Hello world! Nice to meet you, I'm CEL.
Example (GlobalOverload) 
package main

import (
	"fmt"
	"log"

	"github.com/google/cel-go/cel"
	"github.com/google/cel-go/common/types"
	"github.com/google/cel-go/common/types/ref"
)

func main() {
	// The GlobalOverload example demonstrates how to define global overload function.
	// Create the CEL environment with declarations for the input attributes and
	// the desired extension functions. In many cases the desired functionality will
	// be present in a built-in function.
	e, err := cel.NewEnv(
		// Identifiers used within this expression.
		cel.Variable("i", cel.StringType),
		cel.Variable("you", cel.StringType),
		// Function to generate shake_hands between two people.
		//    shake_hands(i,you)
		cel.Function("shake_hands",
			cel.Overload("shake_hands_string_string", []*cel.Type{cel.StringType, cel.StringType}, cel.StringType,
				cel.BinaryBinding(func(arg1, arg2 ref.Val) ref.Val {
					return types.String(fmt.Sprintf("%v and %v are shaking hands.\n", arg1, arg2))
				}),
			),
		),
	)
	if err != nil {
		log.Fatalf("environment creation error: %s\n", err)
	}

	// Compile the expression.
	ast, iss := e.Compile(`shake_hands(i,you)`)
	if iss.Err() != nil {
		log.Fatalln(iss.Err())
	}

	// Create the program.
	prg, err := e.Program(ast)
	if err != nil {
		log.Fatalf("program creation error: %s\n", err)
	}

	// Evaluate the program against some inputs. Note: the details return is not used.
	out, _, err := prg.Eval(map[string]any{
		"i":   "CEL",
		"you": func() ref.Val { return types.String("world") },
	})
	if err != nil {
		log.Fatalf("runtime error: %s\n", err)
	}

	fmt.Println(out)
}

Output:

CEL and world are shaking hands.
Example (StatefulOverload) 
package main

import (
	"context"
	"fmt"
	"log"

	"github.com/google/cel-go/cel"
	"github.com/google/cel-go/common/types"
	"github.com/google/cel-go/common/types/ref"
)

func main() {
	// makeFetch produces a consistent function signature with a different function
	// implementation depending on the provided context.
	makeFetch := func(ctx any) cel.EnvOption {
		fn := func(arg ref.Val) ref.Val {
			return types.NewErr("stateful context not bound")
		}
		if ctx != nil {
			fn = func(resource ref.Val) ref.Val {
				return types.DefaultTypeAdapter.NativeToValue(
					ctx.(context.Context).Value(contextString(string(resource.(types.String)))),
				)
			}
		}
		return cel.Function("fetch",
			cel.Overload("fetch_string",
				[]*cel.Type{cel.StringType}, cel.StringType,
				cel.UnaryBinding(fn),
			),
		)
	}

	// The base environment declares the fetch function with a dummy binding that errors
	// if it is invoked without being replaced by a subsequent call to `baseEnv.Extend`
	baseEnv, err := cel.NewEnv(
		// Identifiers used within this expression.
		cel.Variable("resource", cel.StringType),
		// Function to fetch a resource.
		//    fetch(resource)
		makeFetch(nil),
	)
	if err != nil {
		log.Fatalf("environment creation error: %s\n", err)
	}
	ast, iss := baseEnv.Compile("fetch('my-resource') == 'my-value'")
	if iss.Err() != nil {
		log.Fatalf("Compile() failed: %v", iss.Err())
	}

	// The runtime environment extends the base environment with a contextual binding for
	// the 'fetch' function.
	ctx := context.WithValue(context.TODO(), contextString("my-resource"), "my-value")
	runtimeEnv, err := baseEnv.Extend(makeFetch(ctx))
	if err != nil {
		log.Fatalf("baseEnv.Extend() failed with error: %s\n", err)
	}
	prg, err := runtimeEnv.Program(ast)
	if err != nil {
		log.Fatalf("runtimeEnv.Program() error: %s\n", err)
	}
	out, _, err := prg.Eval(cel.NoVars())
	if err != nil {
		log.Fatalf("runtime error: %s\n", err)
	}

	fmt.Println(out)
}

type contextString string

Output:

true

Index

Examples

Constants

This section is empty.

Variables

View Source 
var (
	// AnyType represents the google.protobuf.Any type.
	AnyType = &Type{
		kind:        AnyKind,
		runtimeType: types.NewTypeValue("google.protobuf.Any"),
	}
	// BoolType represents the bool type.
	BoolType = &Type{
		kind:        BoolKind,
		runtimeType: types.BoolType,
	}
	// BytesType represents the bytes type.
	BytesType = &Type{
		kind:        BytesKind,
		runtimeType: types.BytesType,
	}
	// DoubleType represents the double type.
	DoubleType = &Type{
		kind:        DoubleKind,
		runtimeType: types.DoubleType,
	}
	// DurationType represents the CEL duration type.
	DurationType = &Type{
		kind:        DurationKind,
		runtimeType: types.DurationType,
	}
	// DynType represents a dynamic CEL type whose type will be determined at runtime from context.
	DynType = &Type{
		kind:        DynKind,
		runtimeType: types.NewTypeValue("dyn"),
	}
	// IntType represents the int type.
	IntType = &Type{
		kind:        IntKind,
		runtimeType: types.IntType,
	}
	// NullType represents the type of a null value.
	NullType = &Type{
		kind:        NullTypeKind,
		runtimeType: types.NullType,
	}
	// StringType represents the string type.
	StringType = &Type{
		kind:        StringKind,
		runtimeType: types.StringType,
	}
	// TimestampType represents the time type.
	TimestampType = &Type{
		kind:        TimestampKind,
		runtimeType: types.TimestampType,
	}
	// TypeType represents a CEL type
	TypeType = &Type{
		kind:        TypeKind,
		runtimeType: types.TypeType,
	}
	// UintType represents a uint type.
	UintType = &Type{
		kind:        UintKind,
		runtimeType: types.UintType,
	}
)
View Source 
var (

	// HasMacro expands "has(m.f)" which tests the presence of a field, avoiding the need to
	// specify the field as a string.
	HasMacro = parser.HasMacro

	// AllMacro expands "range.all(var, predicate)" into a comprehension which ensures that all
	// elements in the range satisfy the predicate.
	AllMacro = parser.AllMacro

	// ExistsMacro expands "range.exists(var, predicate)" into a comprehension which ensures that
	// some element in the range satisfies the predicate.
	ExistsMacro = parser.ExistsMacro

	// ExistsOneMacro expands "range.exists_one(var, predicate)", which is true if for exactly one
	// element in range the predicate holds.
	ExistsOneMacro = parser.ExistsOneMacro

	// MapMacro expands "range.map(var, function)" into a comprehension which applies the function
	// to each element in the range to produce a new list.
	MapMacro = parser.MapMacro

	// MapFilterMacro expands "range.map(var, predicate, function)" into a comprehension which
	// first filters the elements in the range by the predicate, then applies the transform function
	// to produce a new list.
	MapFilterMacro = parser.MapFilterMacro

	// FilterMacro expands "range.filter(var, predicate)" into a comprehension which filters
	// elements in the range, producing a new list from the elements that satisfy the predicate.
	FilterMacro = parser.FilterMacro

	// StandardMacros provides an alias to all the CEL macros defined in the standard environment.
	StandardMacros = []Macro{
		HasMacro, AllMacro, ExistsMacro, ExistsOneMacro, MapMacro, MapFilterMacro, FilterMacro,
	}

	// NoMacros provides an alias to an empty list of macros
	NoMacros = []Macro{}
)

Functions

func AstToCheckedExpr 

func AstToCheckedExpr(a *Ast) (*exprpb.CheckedExpr, error)

AstToCheckedExpr converts an Ast to an protobuf CheckedExpr value.

If the Ast.IsChecked() returns false, this conversion method will return an error.

func AstToParsedExpr 

func AstToParsedExpr(a *Ast) (*exprpb.ParsedExpr, error)

AstToParsedExpr converts an Ast to an protobuf ParsedExpr value.

func AstToString added in v0.3.0 

func AstToString(a *Ast) (string, error)

AstToString converts an Ast back to a string if possible.

Note, the conversion may not be an exact replica of the original expression, but will produce a string that is semantically equivalent and whose textual representation is stable.

func AttributePattern added in v0.4.0 

func AttributePattern(varName string) *interpreter.AttributePattern

AttributePattern returns an AttributePattern that matches a top-level variable. The pattern is mutable, and its methods support the specification of one or more qualifier patterns.

For example, the AttributePattern(`a`).QualString(`b`) represents a variable access `a` with a string field or index qualification `b`. This pattern will match Attributes `a`, and `a.b`, but not `a.c`.

When using a CEL expression within a container, e.g. a package or namespace, the variable name in the pattern must match the qualified name produced during the variable namespace resolution. For example, when variable `a` is declared within an expression whose container is `ns.app`, the fully qualified variable name may be `ns.app.a`, `ns.a`, or `a` per the CEL namespace resolution rules. Pick the fully qualified variable name that makes sense within the container as the AttributePattern `varName` argument.

See the interpreter.AttributePattern and interpreter.AttributeQualifierPattern for more info about how to create and manipulate AttributePattern values.

func ExistsMacroExpander added in v0.12.0 

func ExistsMacroExpander(meh MacroExprHelper, target *exprpb.Expr, args []*exprpb.Expr) (*exprpb.Expr, *common.Error)

ExistsMacroExpander expands the input call arguments into a comprehension that returns true if any of the elements in the range match the predicate expressions: <iterRange>.exists(<iterVar>, <predicate>)

func ExistsOneMacroExpander added in v0.12.0 

func ExistsOneMacroExpander(meh MacroExprHelper, target *exprpb.Expr, args []*exprpb.Expr) (*exprpb.Expr, *common.Error)

ExistsOneMacroExpander expands the input call arguments into a comprehension that returns true if exactly one of the elements in the range match the predicate expressions: <iterRange>.exists_one(<iterVar>, <predicate>)

func FilterMacroExpander added in v0.12.0 

func FilterMacroExpander(meh MacroExprHelper, target *exprpb.Expr, args []*exprpb.Expr) (*exprpb.Expr, *common.Error)

FilterMacroExpander expands the input call arguments into a comprehension which produces a list which contains only elements which match the provided predicate expression: <iterRange>.filter(<iterVar>, <predicate>)

func FormatType added in v0.7.1 

func FormatType(t *exprpb.Type) string

FormatType converts a type message into a string representation.

func HasMacroExpander added in v0.12.0 

func HasMacroExpander(meh MacroExprHelper, target *exprpb.Expr, args []*exprpb.Expr) (*exprpb.Expr, *common.Error)

HasMacroExpander expands the input call arguments into a presence test, e.g. has(<operand>.field)

func MapMacroExpander added in v0.12.0 

func MapMacroExpander(meh MacroExprHelper, target *exprpb.Expr, args []*exprpb.Expr) (*exprpb.Expr, *common.Error)

MapMacroExpander expands the input call arguments into a comprehension that transforms each element in the input to produce an output list.

There are two call patterns supported by map: 

<iterRange>.map(<iterVar>, <transform>)
<iterRange>.map(<iterVar>, <predicate>, <transform>)

In the second form only iterVar values which return true when provided to the predicate expression are transformed.

func NoVars 

func NoVars() interpreter.Activation

NoVars returns an empty Activation.

func PartialVars added in v0.4.0 

func PartialVars(vars any,
	unknowns ...*interpreter.AttributePattern) (interpreter.PartialActivation, error)

PartialVars returns a PartialActivation which contains variables and a set of AttributePattern values that indicate variables or parts of variables whose value are not yet known.

The `vars` value may either be an interpreter.Activation or any valid input to the interpreter.NewActivation call.

func RefValueToValue added in v0.10.0 

func RefValueToValue(res ref.Val) (*exprpb.Value, error)

RefValueToValue converts between ref.Val and api.expr.Value. The result Value is the serialized proto form. The ref.Val must not be error or unknown.

func TypeToExprType added in v0.12.0 

func TypeToExprType(t *Type) (*exprpb.Type, error)

TypeToExprType converts a CEL-native type representation to a protobuf CEL Type representation.

func ValueToRefValue added in v0.10.0 

func ValueToRefValue(adapter ref.TypeAdapter, v *exprpb.Value) (ref.Val, error)

ValueToRefValue converts between exprpb.Value and ref.Val.

Types

type Ast 

type Ast struct {
	// contains filtered or unexported fields
}

Ast representing the checked or unchecked expression, its source, and related metadata such as source position information.

func CheckedExprToAst 

func CheckedExprToAst(checkedExpr *exprpb.CheckedExpr) *Ast

CheckedExprToAst converts a checked expression proto message to an Ast.

func CheckedExprToAstWithSource added in v0.9.0 

func CheckedExprToAstWithSource(checkedExpr *exprpb.CheckedExpr, src Source) *Ast

CheckedExprToAstWithSource converts a checked expression proto message to an Ast, using the provided Source as the textual contents.

In general the source is not necessary unless the AST has been modified between the `Parse` and `Check` calls as an `Ast` created from the `Parse` step will carry the source through future calls.

Prefer CheckedExprToAst if loading expressions from storage.

func ParsedExprToAst 

func ParsedExprToAst(parsedExpr *exprpb.ParsedExpr) *Ast

ParsedExprToAst converts a parsed expression proto message to an Ast.

func ParsedExprToAstWithSource added in v0.9.0 

func ParsedExprToAstWithSource(parsedExpr *exprpb.ParsedExpr, src Source) *Ast

ParsedExprToAstWithSource converts a parsed expression proto message to an Ast, using the provided Source as the textual contents.

In general you only need this if you need to recheck a previously checked expression, or if you need to separately check a subset of an expression.

Prefer ParsedExprToAst if loading expressions from storage.

func (*Ast) Expr 

func (ast *Ast) Expr() *exprpb.Expr

Expr returns the proto serializable instance of the parsed/checked expression.

func (*Ast) IsChecked 

func (ast *Ast) IsChecked() bool

IsChecked returns whether the Ast value has been successfully type-checked.

func (*Ast) OutputType added in v0.12.0 

func (ast *Ast) OutputType() *Type

OutputType returns the output type of the expression if the Ast has been type-checked, else returns cel.DynType as the parse step cannot infer types.

func (*Ast) ResultType deprecated 

func (ast *Ast) ResultType() *exprpb.Type

ResultType returns the output type of the expression if the Ast has been type-checked, else returns decls.Dyn as the parse step cannot infer the type.

Deprecated: use OutputType

func (*Ast) Source 

func (ast *Ast) Source() Source

Source returns a view of the input used to create the Ast. This source may be complete or constructed from the SourceInfo.

func (*Ast) SourceInfo 

func (ast *Ast) SourceInfo() *exprpb.SourceInfo

SourceInfo returns character offset and newline position information about expression elements.

type Env 

type Env struct {
	Container *containers.Container
	// contains filtered or unexported fields
}

Env encapsulates the context necessary to perform parsing, type checking, or generation of evaluable programs for different expressions.

func NewCustomEnv added in v0.4.0 

func NewCustomEnv(opts ...EnvOption) (*Env, error)

NewCustomEnv creates a custom program environment which is not automatically configured with the standard library of functions and macros documented in the CEL spec.

The purpose for using a custom environment might be for subsetting the standard library produced by the cel.StdLib() function. Subsetting CEL is a core aspect of its design that allows users to limit the compute and memory impact of a CEL program by controlling the functions and macros that may appear in a given expression.

See the EnvOption helper functions for the options that can be used to configure the environment.

func NewEnv 

func NewEnv(opts ...EnvOption) (*Env, error)

NewEnv creates a program environment configured with the standard library of CEL functions and macros. The Env value returned can parse and check any CEL program which builds upon the core features documented in the CEL specification.

See the EnvOption helper functions for the options that can be used to configure the environment.

func (*Env) Check 

func (e *Env) Check(ast *Ast) (*Ast, *Issues)

Check performs type-checking on the input Ast and yields a checked Ast and/or set of Issues.

Checking has failed if the returned Issues value and its Issues.Err() value are non-nil. Issues should be inspected if they are non-nil, but may not represent a fatal error.

It is possible to have both non-nil Ast and Issues values returned from this call: however, the mere presence of an Ast does not imply that it is valid for use.

func (*Env) Compile added in v0.4.0 

func (e *Env) Compile(txt string) (*Ast, *Issues)

Compile combines the Parse and Check phases CEL program compilation to produce an Ast and associated issues.

If an error is encountered during parsing the Compile step will not continue with the Check phase. If non-error issues are encountered during Parse, they may be combined with any issues discovered during Check.

Note, for parse-only uses of CEL use Parse.

func (*Env) CompileSource added in v0.4.0 

func (e *Env) CompileSource(src Source) (*Ast, *Issues)

CompileSource combines the Parse and Check phases CEL program compilation to produce an Ast and associated issues.

If an error is encountered during parsing the CompileSource step will not continue with the Check phase. If non-error issues are encountered during Parse, they may be combined with any issues discovered during Check.

Note, for parse-only uses of CEL use Parse.

func (*Env) EstimateCost added in v0.10.0 

func (e *Env) EstimateCost(ast *Ast, estimator checker.CostEstimator) (checker.CostEstimate, error)

EstimateCost estimates the cost of a type checked CEL expression using the length estimates of input data and extension functions provided by estimator.

func (*Env) Extend added in v0.3.2 

func (e *Env) Extend(opts ...EnvOption) (*Env, error)

Extend the current environment with additional options to produce a new Env.

Note, the extended Env value should not share memory with the original. It is possible, however, that a CustomTypeAdapter or CustomTypeProvider options could provide values which are mutable. To ensure separation of state between extended environments either make sure the TypeAdapter and TypeProvider are immutable, or that their underlying implementations are based on the ref.TypeRegistry which provides a Copy method which will be invoked by this method.

func (*Env) HasFeature added in v0.5.1 

func (e *Env) HasFeature(flag int) bool

HasFeature checks whether the environment enables the given feature flag, as enumerated in options.go.

func (*Env) HasLibrary added in v0.13.0 

func (e *Env) HasLibrary(libName string) bool

HasLibrary returns whether a specific SingletonLibrary has been configured in the environment.

func (*Env) Parse 

func (e *Env) Parse(txt string) (*Ast, *Issues)

Parse parses the input expression value `txt` to a Ast and/or a set of Issues.

This form of Parse creates a Source value for the input `txt` and forwards to the ParseSource method.

func (*Env) ParseSource added in v0.4.0 

func (e *Env) ParseSource(src Source) (*Ast, *Issues)

ParseSource parses the input source to an Ast and/or set of Issues.

Parsing has failed if the returned Issues value and its Issues.Err() value is non-nil. Issues should be inspected if they are non-nil, but may not represent a fatal error.

It is possible to have both non-nil Ast and Issues values returned from this call; however, the mere presence of an Ast does not imply that it is valid for use.

func (*Env) Program 

func (e *Env) Program(ast *Ast, opts ...ProgramOption) (Program, error)

Program generates an evaluable instance of the Ast within the environment (Env).

func (*Env) ResidualAst added in v0.4.0 

func (e *Env) ResidualAst(a *Ast, details *EvalDetails) (*Ast, error)

ResidualAst takes an Ast and its EvalDetails to produce a new Ast which only contains the attribute references which are unknown.

Residual expressions are beneficial in a few scenarios:

- Optimizing constant expression evaluations away. - Indexing and pruning expressions based on known input arguments. - Surfacing additional requirements that are needed in order to complete an evaluation. - Sharing the evaluation of an expression across multiple machines/nodes.

For example, if an expression targets a 'resource' and 'request' attribute and the possible values for the resource are known, a PartialActivation could mark the 'request' as an unknown interpreter.AttributePattern and the resulting ResidualAst would be reduced to only the parts of the expression that reference the 'request'.

Note, the expression ids within the residual AST generated through this method have no correlation to the expression ids of the original AST.

See the PartialVars helper for how to construct a PartialActivation.

TODO: Consider adding an option to generate a Program.Residual to avoid round-tripping to an Ast format and then Program again.

func (*Env) TypeAdapter added in v0.2.0 

func (e *Env) TypeAdapter() ref.TypeAdapter

TypeAdapter returns the `ref.TypeAdapter` configured for the environment.

func (*Env) TypeProvider added in v0.2.0 

func (e *Env) TypeProvider() ref.TypeProvider

TypeProvider returns the `ref.TypeProvider` configured for the environment.

func (*Env) UnknownVars added in v0.4.0 

func (e *Env) UnknownVars() interpreter.PartialActivation

UnknownVars returns an interpreter.PartialActivation which marks all variables declared in the Env as unknown AttributePattern values.

Note, the UnknownVars will behave the same as an interpreter.EmptyActivation unless the PartialAttributes option is provided as a ProgramOption.

type EnvOption 

type EnvOption func(e *Env) (*Env, error)

EnvOption is a functional interface for configuring the environment.

func Abbrevs added in v0.6.0 

func Abbrevs(qualifiedNames ...string) EnvOption

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 ClearMacros 

func ClearMacros() EnvOption

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 Container 

func Container(name string) EnvOption

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 CrossTypeNumericComparisons added in v0.10.0 

func CrossTypeNumericComparisons(enabled bool) EnvOption

CrossTypeNumericComparisons makes it possible to compare across numeric types, e.g. double < int

func CustomTypeAdapter added in v0.2.0 

func CustomTypeAdapter(adapter ref.TypeAdapter) EnvOption

CustomTypeAdapter swaps the default ref.TypeAdapter implementation with a custom one.

Note: This option must be specified before the Types and TypeDescs options when used together.

func CustomTypeProvider 

func CustomTypeProvider(provider ref.TypeProvider) EnvOption

CustomTypeProvider swaps the default ref.TypeProvider implementation with a custom one.

Note: This option must be specified before the Types and TypeDescs options when used together.

func Declarations 

func Declarations(decls ...*exprpb.Decl) EnvOption

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 DeclareContextProto added in v0.8.0 

func DeclareContextProto(descriptor protoreflect.MessageDescriptor) EnvOption

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 DefaultUTCTimeZone added in v0.12.0 

func DefaultUTCTimeZone(enabled bool) EnvOption

DefaultUTCTimeZone ensures that time-based operations use the UTC timezone rather than the input time's local timezone.

func EagerlyValidateDeclarations added in v0.11.1 

func EagerlyValidateDeclarations(enabled bool) EnvOption

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 EnableMacroCallTracking added in v0.10.0 

func EnableMacroCallTracking() EnvOption

EnableMacroCallTracking ensures that call expressions which are replaced by macros are tracked in the `SourceInfo` of parsed and checked expressions.

func ExprDeclToDeclaration added in v0.12.0 

func ExprDeclToDeclaration(d *exprpb.Decl) (EnvOption, error)

ExprDeclToDeclaration converts a protobuf CEL declaration to a CEL-native declaration, either a Variable or Function.

func Function added in v0.12.0 

func Function(name string, opts ...FunctionOpt) EnvOption

Function defines a function and overloads with optional singleton or per-overload bindings.

Using Function is roughly equivalent to calling Declarations() to declare the function signatures and Functions() to define the function bindings, if they have been defined. Specifying the same function name more than once will result in the aggregation of the function overloads. If any signatures conflict between the existing and new function definition an error will be raised. However, if the signatures are identical and the overload ids are the same, the redefinition will be considered a no-op.

One key difference with using Function() is that each FunctionDecl provided will handle dynamic dispatch based on the type-signatures of the overloads provided which means overload resolution at runtime is handled out of the box rather than via a custom binding for overload resolution via Functions():

- Overloads are searched in the order they are declared - Dynamic dispatch for lists and maps is limited by inspection of the list and map contents 

at runtime. Empty lists and maps will result in a 'default dispatch'

- In the event that a default dispatch occurs, the first overload provided is the one invoked

If you intend to use overloads which differentiate based on the key or element type of a list or map, consider using a generic function instead: e.g. func(list(T)) or func(map(K, V)) as this will allow your implementation to determine how best to handle dispatch and the default behavior for empty lists and maps whose contents cannot be inspected.

For functions which use parameterized opaque types (abstract types), consider using a singleton function which is capable of inspecting the contents of the type and resolving the appropriate overload as CEL can only make inferences by type-name regarding such types.

func HomogeneousAggregateLiterals added in v0.2.0 

func HomogeneousAggregateLiterals() EnvOption

HomogeneousAggregateLiterals option ensures that list and map literal entry types must agree during type-checking.

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 Lib added in v0.4.0 

func Lib(l Library) EnvOption

Lib creates an EnvOption out of a Library, allowing libraries to be provided as functional args, and to be linked to each other.

func Macros 

func Macros(macros ...Macro) EnvOption

Macros option extends the macro set configured in the environment.

Note: This option must be specified after ClearMacros if used together.

func OptionalTypes added in v0.13.0 

func OptionalTypes() EnvOption

OptionalTypes enable support for optional syntax and types in CEL. The optional value type makes it possible to express whether variables have been provided, whether a result has been computed, and in the future whether an object field path, map key value, or list index has a value.

func ParserRecursionLimit added in v0.13.0 

func ParserRecursionLimit(limit int) EnvOption

ParserRecursionLimit adjusts the AST depth the parser will tolerate. Defaults defined in the parser package.

func StdLib added in v0.4.0 

func StdLib() EnvOption

StdLib returns an EnvOption for the standard library of CEL functions and macros.

func TypeDescs added in v0.2.0 

func TypeDescs(descs ...any) EnvOption

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 Types 

func Types(addTypes ...any) EnvOption

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 Variable added in v0.12.0 

func Variable(name string, t *Type) EnvOption

Variable creates an instance of a variable declaration with a variable name and type.

type EvalDetails 

type EvalDetails struct {
	// contains filtered or unexported fields
}

EvalDetails holds additional information observed during the Eval() call.

func (*EvalDetails) ActualCost added in v0.10.0 

func (ed *EvalDetails) ActualCost() *uint64

ActualCost returns the tracked cost through the course of execution when `CostTracking` is enabled. Otherwise, returns nil if the cost was not enabled.

func (*EvalDetails) State 

func (ed *EvalDetails) State() interpreter.EvalState

State of the evaluation, non-nil if the OptTrackState or OptExhaustiveEval is specified within EvalOptions.

type EvalOption 

type EvalOption int

EvalOption indicates an evaluation option that may affect the evaluation behavior or information in the output result. 

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.
	OptCheckStringFormat EvalOption = 1 << iota
)

type FunctionOpt added in v0.12.0 

type FunctionOpt func(*functionDecl) (*functionDecl, error)

FunctionOpt defines a functional option for configuring a function declaration.

func MemberOverload added in v0.12.0 

func MemberOverload(overloadID string, args []*Type, resultType *Type, opts ...OverloadOpt) FunctionOpt

MemberOverload defines a new receiver-style overload (or member function) with an overload id, argument types, and result type. Through the use of OverloadOpt options, the overload may also be configured with a binding, an operand trait, and to be non-strict.

Note: function bindings should be commonly configured with Overload instances whereas operand traits and strict-ness should be rare occurrences.

func Overload added in v0.12.0 

func Overload(overloadID string, args []*Type, resultType *Type, opts ...OverloadOpt) FunctionOpt

Overload defines a new global overload with an overload id, argument types, and result type. Through the use of OverloadOpt options, the overload may also be configured with a binding, an operand trait, and to be non-strict.

Note: function bindings should be commonly configured with Overload instances whereas operand traits and strict-ness should be rare occurrences.

func SingletonBinaryBinding added in v0.13.0 

func SingletonBinaryBinding(fn functions.BinaryOp, traits ...int) FunctionOpt

SingletonBinaryBinding creates a singleton function definition to be used with all function overloads.

Note, this approach works well if operand is expected to have a specific trait which it implements, e.g. traits.ContainerType. Otherwise, prefer per-overload function bindings.

func SingletonBinaryImpl deprecated added in v0.12.0 

func SingletonBinaryImpl(fn functions.BinaryOp, traits ...int) FunctionOpt

SingletonBinaryImpl creates a singleton function definition to be used with all function overloads.

Note, this approach works well if operand is expected to have a specific trait which it implements, e.g. traits.ContainerType. Otherwise, prefer per-overload function bindings.

Deprecated: use SingletonBinaryBinding

func SingletonFunctionBinding added in v0.13.0 

func SingletonFunctionBinding(fn functions.FunctionOp, traits ...int) FunctionOpt

SingletonFunctionBinding creates a singleton function definition to be used with all function overloads.

Note, this approach works well if operand is expected to have a specific trait which it implements, e.g. traits.ContainerType. Otherwise, prefer per-overload function bindings.

func SingletonFunctionImpl deprecated added in v0.12.0 

func SingletonFunctionImpl(fn functions.FunctionOp, traits ...int) FunctionOpt

SingletonFunctionImpl creates a singleton function definition to be used with all function overloads.

Note, this approach works well if operand is expected to have a specific trait which it implements, e.g. traits.ContainerType. Otherwise, prefer per-overload function bindings.

Deprecated: use SingletonFunctionBinding

func SingletonUnaryBinding added in v0.12.0 

func SingletonUnaryBinding(fn functions.UnaryOp, traits ...int) FunctionOpt

SingletonUnaryBinding creates a singleton function definition to be used for all function overloads.

Note, this approach works well if operand is expected to have a specific trait which it implements, e.g. traits.ContainerType. Otherwise, prefer per-overload function bindings.

type Issues 

type Issues struct {
	// contains filtered or unexported fields
}

Issues defines methods for inspecting the error details of parse and check calls.

Note: in the future, non-fatal warnings and notices may be inspectable via the Issues struct.

func NewIssues added in v0.4.0 

func NewIssues(errs *common.Errors) *Issues

NewIssues returns an Issues struct from a common.Errors object.

func (*Issues) Append added in v0.4.0 

func (i *Issues) Append(other *Issues) *Issues

Append collects the issues from another Issues struct into a new Issues object.

func (*Issues) Err 

func (i *Issues) Err() error

Err returns an error value if the issues list contains one or more errors.

func (*Issues) Errors 

func (i *Issues) Errors() []common.Error

Errors returns the collection of errors encountered in more granular detail.

func (*Issues) String added in v0.4.0 

func (i *Issues) String() string

String converts the issues to a suitable display string.

type Kind added in v0.12.0 

type Kind uint

Kind indicates a CEL type's kind which is used to differentiate quickly between simple and complex types. 

const (
	// DynKind represents a dynamic type. This kind only exists at type-check time.
	DynKind Kind = iota

	// AnyKind represents a google.protobuf.Any type. This kind only exists at type-check time.
	AnyKind

	// BoolKind represents a boolean type.
	BoolKind

	// BytesKind represents a bytes type.
	BytesKind

	// DoubleKind represents a double type.
	DoubleKind

	// DurationKind represents a CEL duration type.
	DurationKind

	// IntKind represents an integer type.
	IntKind

	// ListKind represents a list type.
	ListKind

	// MapKind represents a map type.
	MapKind

	// NullTypeKind represents a null type.
	NullTypeKind

	// OpaqueKind represents an abstract type which has no accessible fields.
	OpaqueKind

	// StringKind represents a string type.
	StringKind

	// StructKind represents a structured object with typed fields.
	StructKind

	// TimestampKind represents a a CEL time type.
	TimestampKind

	// TypeKind represents the CEL type.
	TypeKind

	// TypeParamKind represents a parameterized type whose type name will be resolved at type-check time, if possible.
	TypeParamKind

	// UintKind represents a uint type.
	UintKind
)

type Library added in v0.4.0 

type Library interface {
	// CompileOptions returns a collection of functional options for configuring the Parse / Check
	// environment.
	CompileOptions() []EnvOption

	// ProgramOptions returns a collection of functional options which should be included in every
	// Program generated from the Env.Program() call.
	ProgramOptions() []ProgramOption
}

Library provides a collection of EnvOption and ProgramOption values used to configure a CEL environment for a particular use case or with a related set of functionality.

Note, the ProgramOption values provided by a library are expected to be static and not vary between calls to Env.Program(). If there is a need for such dynamic configuration, prefer to configure these options outside the Library and within the Env.Program() call directly.

type Macro added in v0.12.0 

type Macro = parser.Macro

Macro describes a function signature to match and the MacroExpander to apply.

Note: when a Macro should apply to multiple overloads (based on arg count) of a given function, a Macro should be created per arg-count or as a var arg macro.

func NewGlobalMacro added in v0.12.0 

func NewGlobalMacro(function string, argCount int, expander MacroExpander) Macro

NewGlobalMacro creates a Macro for a global function with the specified arg count.

func NewGlobalVarArgMacro added in v0.12.0 

func NewGlobalVarArgMacro(function string, expander MacroExpander) Macro

NewGlobalVarArgMacro creates a Macro for a global function with a variable arg count.

func NewReceiverMacro added in v0.12.0 

func NewReceiverMacro(function string, argCount int, expander MacroExpander) Macro

NewReceiverMacro creates a Macro for a receiver function matching the specified arg count.

func NewReceiverVarArgMacro added in v0.12.0 

func NewReceiverVarArgMacro(function string, expander MacroExpander) Macro

NewReceiverVarArgMacro creates a Macro for a receiver function matching a variable arg count.

type MacroExpander added in v0.12.0 

type MacroExpander = parser.MacroExpander

MacroExpander converts a call and its associated arguments into a new CEL abstract syntax tree.

If the MacroExpander determines within the implementation that an expansion is not needed it may return a nil Expr value to indicate a non-match. However, if an expansion is to be performed, but the arguments are not well-formed, the result of the expansion will be an error.

The MacroExpander accepts as arguments a MacroExprHelper as well as the arguments used in the function call and produces as output an Expr ast node.

Note: when the Macro.IsReceiverStyle() method returns true, the target argument will be nil.

type MacroExprHelper added in v0.12.0 

type MacroExprHelper = parser.ExprHelper

MacroExprHelper exposes helper methods for creating new expressions within a CEL abstract syntax tree.

type OverloadOpt added in v0.12.0 

type OverloadOpt func(*overloadDecl) (*overloadDecl, error)

OverloadOpt is a functional option for configuring a function overload.

func BinaryBinding added in v0.12.0 

func BinaryBinding(binding functions.BinaryOp) OverloadOpt

BinaryBinding provides the implementation of a binary overload. The provided function is protected by a runtime type-guard which ensures runtime type agreement between the overload signature and runtime argument types.

func FunctionBinding added in v0.12.0 

func FunctionBinding(binding functions.FunctionOp) OverloadOpt

FunctionBinding provides the implementation of a variadic overload. The provided function is protected by a runtime type-guard which ensures runtime type agreement between the overload signature and runtime argument types.

func OverloadIsNonStrict added in v0.12.0 

func OverloadIsNonStrict() OverloadOpt

OverloadIsNonStrict enables the function to be called with error and unknown argument values.

Note: do not use this option unless absoluately necessary as it should be an uncommon feature.

func OverloadOperandTrait added in v0.12.0 

func OverloadOperandTrait(trait int) OverloadOpt

OverloadOperandTrait configures a set of traits which the first argument to the overload must implement in order to be successfully invoked.

func UnaryBinding added in v0.12.0 

func UnaryBinding(binding functions.UnaryOp) OverloadOpt

UnaryBinding provides the implementation of a unary overload. The provided function is protected by a runtime type-guard which ensures runtime type agreement between the overload signature and runtime argument types.

type Program 

type Program interface {
	// Eval returns the result of an evaluation of the Ast and environment against the input vars.
	//
	// The vars value may either be an `interpreter.Activation` or a `map[string]any`.
	//
	// If the `OptTrackState`, `OptTrackCost` or `OptExhaustiveEval` flags are used, the `details` response will
	// be non-nil. Given this caveat on `details`, the return state from evaluation will be:
	//
	// *  `val`, `details`, `nil` - Successful evaluation of a non-error result.
	// *  `val`, `details`, `err` - Successful evaluation to an error result.
	// *  `nil`, `details`, `err` - Unsuccessful evaluation.
	//
	// An unsuccessful evaluation is typically the result of a series of incompatible `EnvOption`
	// or `ProgramOption` values used in the creation of the evaluation environment or executable
	// program.
	Eval(any) (ref.Val, *EvalDetails, error)

	// ContextEval evaluates the program with a set of input variables and a context object in order
	// to support cancellation and timeouts. This method must be used in conjunction with the
	// InterruptCheckFrequency() option for cancellation interrupts to be impact evaluation.
	//
	// The vars value may either be an `interpreter.Activation` or `map[string]any`.
	//
	// The output contract for `ContextEval` is otherwise identical to the `Eval` method.
	ContextEval(context.Context, any) (ref.Val, *EvalDetails, error)
}

Program is an evaluable view of an Ast.

type ProgramOption 

type ProgramOption func(p *prog) (*prog, error)

ProgramOption is a functional interface for configuring evaluation bindings and behaviors.

func CostLimit added in v0.10.0 

func CostLimit(costLimit uint64) ProgramOption

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 CostTracking added in v0.10.0 

func CostTracking(costEstimator interpreter.ActualCostEstimator) ProgramOption

CostTracking enables cost tracking and registers a ActualCostEstimator that can optionally provide a runtime cost estimate for any function calls.

func CustomDecorator added in v0.6.0 

func CustomDecorator(dec interpreter.InterpretableDecorator) ProgramOption

CustomDecorator appends an InterpreterDecorator to the program.

InterpretableDecorators can be used to inspect, alter, or replace the Program plan.

func EvalOptions 

func EvalOptions(opts ...EvalOption) ProgramOption

EvalOptions sets one or more evaluation options which may affect the evaluation or Result.

func Functions deprecated 

func Functions(funcs ...*functions.Overload) ProgramOption

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 Globals 

func Globals(vars any) ProgramOption

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 InterruptCheckFrequency added in v0.10.0 

func InterruptCheckFrequency(checkFrequency uint) ProgramOption

InterruptCheckFrequency configures the number of iterations within a comprehension to evaluate before checking whether the function evaluation has been interrupted.

func OptimizeRegex added in v0.10.0 

func OptimizeRegex(regexOptimizations ...*interpreter.RegexOptimization) ProgramOption

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.

type SingletonLibrary added in v0.13.0 

type SingletonLibrary interface {
	Library

	// LibraryName provides a namespaced name which is used to check whether the library has already
	// been configured in the environment.
	LibraryName() string
}

SingletonLibrary refines the Library interface to ensure that libraries in this format are only configured once within the environment.

type Source 

type Source = common.Source

Source interface representing a user-provided expression.

type Type added in v0.12.0 

type Type struct {
	// contains filtered or unexported fields
}

Type holds a reference to a runtime type with an optional type-checked set of type parameters.

func ExprTypeToType added in v0.12.0 

func ExprTypeToType(t *exprpb.Type) (*Type, error)

ExprTypeToType converts a protobuf CEL type representation to a CEL-native type representation.

func ListType added in v0.12.0 

func ListType(elemType *Type) *Type

ListType creates an instances of a list type value with the provided element type.

func MapType added in v0.12.0 

func MapType(keyType, valueType *Type) *Type

MapType creates an instance of a map type value with the provided key and value types.

func NullableType added in v0.12.0 

func NullableType(wrapped *Type) *Type

NullableType creates an instance of a nullable type with the provided wrapped type.

Note: only primitive types are supported as wrapped types.

func ObjectType added in v0.12.0 

func ObjectType(typeName string) *Type

ObjectType creates a type references to an externally defined type, e.g. a protobuf message type.

func OpaqueType added in v0.12.0 

func OpaqueType(name string, params ...*Type) *Type

OpaqueType creates an abstract parameterized type with a given name.

func OptionalType added in v0.13.0 

func OptionalType(param *Type) *Type

OptionalType creates an abstract parameterized type instance corresponding to CEL's notion of optional.

func TypeParamType added in v0.12.0 

func TypeParamType(paramName string) *Type

TypeParamType creates a parameterized type instance.

func (*Type) IsAssignableRuntimeType added in v0.12.0 

func (t *Type) IsAssignableRuntimeType(val ref.Val) bool

IsAssignableRuntimeType determines whether the current type is runtime assignable from the input runtimeType.

At runtime, parameterized types are erased and so a function which type-checks to support a map(string, string) will have a runtime assignable type of a map.

func (*Type) IsAssignableType added in v0.12.0 

func (t *Type) IsAssignableType(fromType *Type) bool

IsAssignableType determines whether the current type is type-check assignable from the input fromType.

func (*Type) String added in v0.12.0 

func (t *Type) String() string

String returns a human-readable definition of the type name.

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