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eval.go
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eval.go
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// © 2022-2023 Snyk Limited All rights reserved.
//
// 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 arm
import (
"strings"
)
// Makes state available to ARM template function evaluation. It contains
// references to implementations of functions, and the other fields exist to
// pass data to certain function impls other than what is already in their args.
type EvaluationContext struct {
Functions map[string]Function
}
type Function func(args ...interface{}) (interface{}, error)
// Detects whether an ARM string is an expression (enclosed by []), and
// tries to evaluate it if so.
func (e *EvaluationContext) EvaluateTemplateString(input string) (interface{}, error) {
if !IsTemplateExpression(input) {
return input, nil
}
evaluated, err := e.eval(extractAndEscapeTemplateString(input))
if err != nil {
if armErr, ok := err.(Error); ok {
armErr.expression = input
err = armErr
}
}
return evaluated, err
}
func IsTemplateExpression(input string) bool {
return strings.HasPrefix(input, "[") && strings.HasSuffix(input, "]")
}
// https://learn.microsoft.com/en-us/azure/azure-resource-manager/templates/template-expressions#escape-characters
func extractAndEscapeTemplateString(input string) string {
// Remove brackets
input = input[1:(len(input) - 1)]
return strings.ReplaceAll(
strings.ReplaceAll(
input, "[[", "[",
), "]]", "]",
)
}
func (e *EvaluationContext) eval(input string) (interface{}, error) {
tokens, err := tokenize(input)
if err != nil {
return nil, err
}
expr, err := parse(tokens)
if err != nil {
return nil, err
}
return e.evalExpr(expr)
}
func (e *EvaluationContext) evalExpr(expr expression) (interface{}, error) {
return expr.eval(e)
}