functions.go

package template

// Copyright (c) 2018 Bhojpur Consulting Private Limited, India. All rights reserved.

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

import (
	"bytes"
	"encoding/json"
	"fmt"
	"strings"
	"text/template"

	"github.com/Masterminds/sprig/v3"
	"github.com/pelletier/go-toml"
	"github.com/pkg/errors"
	"gopkg.in/yaml.v2"
)

const recursionMaxNums = 1000

// funcMap returns a mapping of all of the functions that Engine has.
//
// Because some functions are late-bound (e.g. contain context-sensitive
// data), the functions may not all perform identically outside of an Engine
// as they will inside of an Engine.
//
// Known late-bound functions:
//	- "include"
//	- "tpl"
//
// These are late-bound in Engine.Render().  The
// version included in the FuncMap is a placeholder.
//
func funcMap() template.FuncMap {
	f := sprig.TxtFuncMap()

	// Add some extra functionality
	extra := template.FuncMap{
		"toToml":        toTOML,
		"toYaml":        toYAML,
		"fromYaml":      fromYAML,
		"fromYamlArray": fromYAMLArray,
		"toJson":        toJSON,
		"fromJson":      fromJSON,
		"fromJsonArray": fromJSONArray,

		// This is a placeholder for the "include" function, which is
		// late-bound to a template. By declaring it here, we preserve the
		// integrity of the linter.
		"include": func(string, interface{}) string { return "not implemented" },
	}

	for k, v := range extra {
		f[k] = v
	}

	return f
}

// toYAML takes an interface, marshals it to yaml, and returns a string. It will
// always return a string, even on marshal error (empty string).
//
// This is designed to be called from a template.
func toYAML(v interface{}) string {
	data, err := yaml.Marshal(v)
	if err != nil {
		// Swallow errors inside of a template.
		return ""
	}
	return strings.TrimSuffix(string(data), "\n")
}

// fromYAML converts a YAML document into a map[string]interface{}.
//
// This is not a general-purpose YAML parser, and will not parse all valid
// YAML documents. Additionally, because its intended use is within templates
// it tolerates errors. It will insert the returned error message string into
// m["Error"] in the returned map.
func fromYAML(str string) map[string]interface{} {
	m := map[string]interface{}{}

	if err := yaml.Unmarshal([]byte(str), &m); err != nil {
		m["Error"] = err.Error()
	}
	return m
}

// fromYAMLArray converts a YAML array into a []interface{}.
//
// This is not a general-purpose YAML parser, and will not parse all valid
// YAML documents. Additionally, because its intended use is within templates
// it tolerates errors. It will insert the returned error message string as
// the first and only item in the returned array.
func fromYAMLArray(str string) []interface{} {
	a := []interface{}{}

	if err := yaml.Unmarshal([]byte(str), &a); err != nil {
		a = []interface{}{err.Error()}
	}
	return a
}

// toTOML takes an interface, marshals it to toml, and returns a string. It will
// always return a string, even on marshal error (empty string).
//
// This is designed to be called from a template.
func toTOML(v interface{}) string {
	b := bytes.NewBuffer(nil)
	e := toml.NewEncoder(b)
	err := e.Encode(v)
	if err != nil {
		return err.Error()
	}
	return b.String()
}

// toJSON takes an interface, marshals it to json, and returns a string. It will
// always return a string, even on marshal error (empty string).
//
// This is designed to be called from a template.
func toJSON(v interface{}) string {
	data, err := json.Marshal(v)
	if err != nil {
		// Swallow errors inside of a template.
		return ""
	}
	return string(data)
}

// fromJSON converts a JSON document into a map[string]interface{}.
//
// This is not a general-purpose JSON parser, and will not parse all valid
// JSON documents. Additionally, because its intended use is within templates
// it tolerates errors. It will insert the returned error message string into
// m["Error"] in the returned map.
func fromJSON(str string) map[string]interface{} {
	m := make(map[string]interface{})

	if err := json.Unmarshal([]byte(str), &m); err != nil {
		m["Error"] = err.Error()
	}
	return m
}

// fromJSONArray converts a JSON array into a []interface{}.
//
// This is not a general-purpose JSON parser, and will not parse all valid
// JSON documents. Additionally, because its intended use is within templates
// it tolerates errors. It will insert the returned error message string as
// the first and only item in the returned array.
func fromJSONArray(str string) []interface{} {
	a := []interface{}{}

	if err := json.Unmarshal([]byte(str), &a); err != nil {
		a = []interface{}{err.Error()}
	}
	return a
}

func includeTemplate(tmpl *template.Template, includedNames map[string]int) func(name string, data interface{}) (string, error) {
	return func(name string, data interface{}) (string, error) {
		var buf strings.Builder
		if v, ok := includedNames[name]; ok {
			if v > recursionMaxNums {
				return "", errors.Wrapf(fmt.Errorf("unable to execute template"), "rendering template has a nested reference name: %s", name)
			}
			includedNames[name]++
		} else {
			includedNames[name] = 1
		}
		err := tmpl.ExecuteTemplate(&buf, name, data)
		includedNames[name]--
		return buf.String(), err
	}
}