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cel.go
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cel.go
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// Copyright 2021-2023 Zenauth Ltd.
// SPDX-License-Identifier: Apache-2.0
package conditions
import (
"fmt"
"strings"
"github.com/google/cel-go/cel"
"github.com/google/cel-go/checker/decls"
"github.com/google/cel-go/ext"
exprpb "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
enginev1 "github.com/cerbos/cerbos/api/genpb/cerbos/engine/v1"
requestv1 "github.com/cerbos/cerbos/api/genpb/cerbos/request/v1"
"github.com/cerbos/cerbos/internal/conditions/types"
)
const (
CELRequestIdent = "request"
CELResourceAbbrev = "R"
CELResourceField = "resource"
CELPrincipalAbbrev = "P"
CELPrincipalField = "principal"
CELVariablesIdent = "variables"
CELVariablesAbbrev = "V"
CELGlobalsIdent = "globals"
CELGlobalsAbbrev = "G"
CELAuxDataField = "aux_data"
CELAttrField = "attr"
)
var (
StdEnv *cel.Env
StdPartialEnv *cel.Env
TrueExpr *exprpb.CheckedExpr
FalseExpr *exprpb.CheckedExpr
)
var StdEnvDecls = []*exprpb.Decl{
decls.NewVar(CELRequestIdent, decls.NewObjectType("cerbos.engine.v1.CheckInput")),
decls.NewVar(CELPrincipalAbbrev, decls.NewObjectType("cerbos.engine.v1.Principal")),
decls.NewVar(CELResourceAbbrev, decls.NewObjectType("cerbos.engine.v1.Resource")),
decls.NewVar(CELVariablesIdent, decls.NewMapType(decls.String, decls.Dyn)),
decls.NewVar(CELVariablesAbbrev, decls.NewMapType(decls.String, decls.Dyn)),
decls.NewVar(CELGlobalsIdent, decls.NewMapType(decls.String, decls.Dyn)),
decls.NewVar(CELGlobalsAbbrev, decls.NewMapType(decls.String, decls.Dyn)),
}
func init() {
var err error
StdEnv, err = initEnv(newCELEnvOptions())
if err != nil {
panic(fmt.Errorf("failed to initialize standard CEL environment: %w", err))
}
StdPartialEnv, err = initEnv(newCELQueryPlanEnvOptions())
if err != nil {
panic(fmt.Errorf("failed to initialize CEL environment for partial evaluation: %w", err))
}
FalseExpr, err = compileConstant("false")
if err != nil {
panic(fmt.Errorf("failed to compile constant 'false': %w", err))
}
TrueExpr, err = compileConstant("true")
if err != nil {
panic(fmt.Errorf("failed to compile constant 'true': %w", err))
}
}
func initEnv(options []cel.EnvOption) (*cel.Env, error) {
env, err := cel.NewEnv(options...)
if err != nil {
return nil, err
}
cctp := types.NewCamelCaseFieldProvider(env.CELTypeProvider())
return env.Extend(cel.CustomTypeProvider(cctp))
}
func compileConstant(value string) (*exprpb.CheckedExpr, error) {
ast, iss := StdEnv.Compile(value)
if iss.Err() != nil {
return nil, fmt.Errorf("failed to compile constant %q: %w", value, iss.Err())
}
expr, err := cel.AstToCheckedExpr(ast)
if err != nil {
return nil, fmt.Errorf("failed to convert constant %q to checked expression: %w", value, err)
}
return expr, nil
}
func Fqn(s string) string {
return fmt.Sprintf("%s.%s", CELRequestIdent, s)
}
func ResourceAttributeNames(s string) []string {
return []string{
fmt.Sprintf("%s.%s.%s", CELResourceAbbrev, CELAttrField, s), // R.attr.<s>
fmt.Sprintf("%s.%s.%s", Fqn(CELResourceField), CELAttrField, s), // request.resource.attr.<s>
}
}
func ExpandAbbrev(s string) string {
prefix, rest, ok := strings.Cut(s, ".")
expanded := prefix
switch prefix {
case CELPrincipalAbbrev:
expanded = Fqn(CELPrincipalField)
case CELResourceAbbrev:
expanded = Fqn(CELResourceField)
case CELVariablesAbbrev:
expanded = CELVariablesIdent
case CELGlobalsAbbrev:
expanded = CELGlobalsIdent
}
if ok {
return fmt.Sprintf("%s.%s", expanded, rest)
}
return expanded
}
func newCELQueryPlanEnvOptions() []cel.EnvOption {
return []cel.EnvOption{
cel.CrossTypeNumericComparisons(true),
cel.Types(&requestv1.PlanResourcesRequest{}, &enginev1.Principal{}, &enginev1.Resource{}),
cel.Declarations(
decls.NewVar(CELRequestIdent, decls.NewObjectType("cerbos.request.v1.ResourcesQueryPlanRequest")),
decls.NewVar(Fqn(CELPrincipalField), decls.NewObjectType("cerbos.engine.v1.Principal")),
decls.NewVar(Fqn(CELResourceField), decls.NewObjectType("cerbos.engine.v1.Resource")),
decls.NewVar(Fqn(CELAuxDataField), decls.NewObjectType("cerbos.engine.v1.AuxData")),
decls.NewVar(CELPrincipalAbbrev, decls.NewObjectType("cerbos.engine.v1.Principal")),
decls.NewVar(CELResourceAbbrev, decls.NewObjectType("cerbos.engine.v1.Resource")),
decls.NewVar(CELVariablesIdent, decls.NewMapType(decls.String, decls.Dyn)),
decls.NewVar(CELVariablesAbbrev, decls.NewMapType(decls.String, decls.Dyn)),
decls.NewVar(CELGlobalsIdent, decls.NewMapType(decls.String, decls.Dyn)),
decls.NewVar(CELGlobalsAbbrev, decls.NewMapType(decls.String, decls.Dyn)),
),
ext.Strings(),
ext.Encoders(),
ext.Math(),
CerbosCELLib(),
}
}
func newCELEnvOptions() []cel.EnvOption {
return []cel.EnvOption{
cel.CrossTypeNumericComparisons(true),
cel.Types(&enginev1.CheckInput{}, &enginev1.Principal{}, &enginev1.Resource{}),
cel.Declarations(StdEnvDecls...),
ext.Strings(),
ext.Encoders(),
ext.Math(),
CerbosCELLib(),
}
}