emissary/internal/config/environment.go

package config

import (
	"os"
	"regexp"
	"strconv"
	"time"

	"github.com/pkg/errors"
	"gopkg.in/yaml.v3"
)

var (
	interpolationRegExp          = regexp.MustCompile(`^\${((?P<varName>\w+)|((?P<varNameWithDefault>\w+):-(?P<defaultValue>[^}]+)))}$`)
	varNameGroupIndex            = interpolationRegExp.SubexpIndex("varName")
	varNameWithDefaultGroupIndex = interpolationRegExp.SubexpIndex("varNameWithDefault")
	defaultValueGroupIndex       = interpolationRegExp.SubexpIndex("defaultValue")
)

func interpolate(str string, getValueFunc func(name string) string) string {
	for _, match := range interpolationRegExp.FindAllStringSubmatch(str, -1) {
		varName := match[varNameWithDefaultGroupIndex]
		if varName == "" {
			varName = match[varNameGroupIndex]
		}

		if varName == "" {
			continue
		}

		defaultValue := ""
		if defaultValueGroupIndex < len(match) {
			defaultValue = match[defaultValueGroupIndex]
		}

		str = getValueFunc(varName)
		if str == "" {
			str = defaultValue
		}
	}

	return str
}

func interpolateEnv(str string) string {
	return interpolate(str, os.Getenv)
}

type InterpolatedString string

func (is *InterpolatedString) UnmarshalYAML(value *yaml.Node) error {
	var str string

	if err := value.Decode(&str); err != nil {
		return errors.WithStack(err)
	}

	*is = InterpolatedString(interpolateEnv(str))

	return nil
}

type InterpolatedInt int

func (ii *InterpolatedInt) UnmarshalYAML(value *yaml.Node) error {
	var str string

	if err := value.Decode(&str); err != nil {
		return errors.Wrapf(err, "could not decode value '%v' (line '%d') into string", value.Value, value.Line)
	}

	str = interpolateEnv(str)

	intVal, err := strconv.ParseInt(str, 10, 32)
	if err != nil {
		return errors.Wrapf(err, "could not parse int '%v',  line '%d'", str, value.Line)
	}

	*ii = InterpolatedInt(int(intVal))

	return nil
}

type InterpolatedBool bool

func (ib *InterpolatedBool) UnmarshalYAML(value *yaml.Node) error {
	var str string

	if err := value.Decode(&str); err != nil {
		return errors.Wrapf(err, "could not decode value '%v' (line '%d') into string", value.Value, value.Line)
	}

	str = interpolateEnv(str)

	boolVal, err := strconv.ParseBool(str)
	if err != nil {
		return errors.Wrapf(err, "could not parse bool '%v',  line '%d'", str, value.Line)
	}

	*ib = InterpolatedBool(boolVal)

	return nil
}

type InterpolatedMap map[string]interface{}

func (im *InterpolatedMap) UnmarshalYAML(value *yaml.Node) error {
	var data map[string]interface{}

	if err := value.Decode(&data); err != nil {
		return errors.Wrapf(err, "could not decode value '%v' (line '%d') into map", value.Value, value.Line)
	}

	for key, value := range data {
		strVal, ok := value.(string)
		if !ok {
			continue
		}

		strVal = interpolateEnv(strVal)

		data[key] = strVal
	}

	*im = data

	return nil
}

type InterpolatedStringSlice []string

func (iss *InterpolatedStringSlice) UnmarshalYAML(value *yaml.Node) error {
	var data []string

	if err := value.Decode(&data); err != nil {
		return errors.Wrapf(err, "could not decode value '%v' (line '%d') into map", value.Value, value.Line)
	}

	for index, value := range data {
		value = interpolateEnv(value)

		data[index] = value
	}

	*iss = data

	return nil
}

type InterpolatedDuration time.Duration

func (id *InterpolatedDuration) UnmarshalYAML(value *yaml.Node) error {
	var str string

	if err := value.Decode(&str); err != nil {
		return errors.Wrapf(err, "could not decode value '%v' (line '%d') into string", value.Value, value.Line)
	}

	str = interpolateEnv(str)

	duration, err := time.ParseDuration(str)
	if err != nil {
		return errors.Wrapf(err, "could not parse duration '%v',  line '%d'", str, value.Line)
	}

	*id = InterpolatedDuration(duration)

	return nil
}

func (id *InterpolatedDuration) MarshalYAML() (interface{}, error) {
	duration := time.Duration(*id)

	return duration.String(), nil
}

func NewInterpolatedDuration(d time.Duration) *InterpolatedDuration {
	id := InterpolatedDuration(d)
	return &id
}