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// Copyright 2022 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 ext
import (
"github.com/google/cel-go/cel"
"github.com/google/cel-go/common/ast"
)
// Protos returns a cel.EnvOption to configure extended macros and functions for
// proto manipulation.
//
// Note, all macros use the 'proto' namespace; however, at the time of macro
// expansion the namespace looks just like any other identifier. If you are
// currently using a variable named 'proto', the macro will likely work just as
// intended; however, there is some chance for collision.
//
// # Protos.GetExt
//
// Macro which generates a select expression that retrieves an extension field
// from the input proto2 syntax message. If the field is not set, the default
// value forthe extension field is returned according to safe-traversal semantics.
//
// proto.getExt(<msg>, <fully.qualified.extension.name>) -> <field-type>
//
// Examples:
//
// proto.getExt(msg, google.expr.proto2.test.int32_ext) // returns int value
//
// # Protos.HasExt
//
// Macro which generates a test-only select expression that determines whether
// an extension field is set on a proto2 syntax message.
//
// proto.hasExt(<msg>, <fully.qualified.extension.name>) -> <bool>
//
// Examples:
//
// proto.hasExt(msg, google.expr.proto2.test.int32_ext) // returns true || false
func Protos() cel.EnvOption {
return cel.Lib(protoLib{})
}
var (
protoNamespace = "proto"
hasExtension = "hasExt"
getExtension = "getExt"
)
type protoLib struct{}
// LibraryName implements the SingletonLibrary interface method.
func (protoLib) LibraryName() string {
return "cel.lib.ext.protos"
}
// CompileOptions implements the Library interface method.
func (protoLib) CompileOptions() []cel.EnvOption {
return []cel.EnvOption{
cel.Macros(
// proto.getExt(msg, select_expression)
cel.ReceiverMacro(getExtension, 2, getProtoExt),
// proto.hasExt(msg, select_expression)
cel.ReceiverMacro(hasExtension, 2, hasProtoExt),
),
}
}
// ProgramOptions implements the Library interface method.
func (protoLib) ProgramOptions() []cel.ProgramOption {
return []cel.ProgramOption{}
}
// hasProtoExt generates a test-only select expression for a fully-qualified extension name on a protobuf message.
func hasProtoExt(mef cel.MacroExprFactory, target ast.Expr, args []ast.Expr) (ast.Expr, *cel.Error) {
if !macroTargetMatchesNamespace(protoNamespace, target) {
return nil, nil
}
extensionField, err := getExtFieldName(mef, args[1])
if err != nil {
return nil, err
}
return mef.NewPresenceTest(args[0], extensionField), nil
}
// getProtoExt generates a select expression for a fully-qualified extension name on a protobuf message.
func getProtoExt(mef cel.MacroExprFactory, target ast.Expr, args []ast.Expr) (ast.Expr, *cel.Error) {
if !macroTargetMatchesNamespace(protoNamespace, target) {
return nil, nil
}
extFieldName, err := getExtFieldName(mef, args[1])
if err != nil {
return nil, err
}
return mef.NewSelect(args[0], extFieldName), nil
}
func getExtFieldName(mef cel.MacroExprFactory, expr ast.Expr) (string, *cel.Error) {
isValid := false
extensionField := ""
switch expr.Kind() {
case ast.SelectKind:
extensionField, isValid = validateIdentifier(expr)
}
if !isValid {
return "", mef.NewError(expr.ID(), "invalid extension field")
}
return extensionField, nil
}
func validateIdentifier(expr ast.Expr) (string, bool) {
switch expr.Kind() {
case ast.IdentKind:
return expr.AsIdent(), true
case ast.SelectKind:
sel := expr.AsSelect()
if sel.IsTestOnly() {
return "", false
}
opStr, isIdent := validateIdentifier(sel.Operand())
if !isIdent {
return "", false
}
return opStr + "." + sel.FieldName(), true
default:
return "", false
}
}
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