rules.go

package main

import (
	"errors"
	"fmt"
	"regexp"
	"sync"

	log "github.com/sirupsen/logrus"
	"gopkg.in/yaml.v2"
)

var (
	// In the event of invalid regex, anything for that rule is allowed
	defaultRegex = regexp.MustCompile(".*")
)

// Rules is a slice of rules that are loaded from a yaml array
type rules struct {
	compiledRegexs map[string]*regexp.Regexp
	Rules          []rule `yaml:"rules" json:"rules"`
	mu             sync.Mutex
}

// Rule is a struct that represents a rule within rules array
type rule struct {
	Name  string `yaml:"name" json:"name"`
	Key   string `yaml:"key" json:"key"`
	Value value  `yaml:"value" json:"value"`
}

// Value is struct within each rule which only supports regex, but can be expanded
type value struct {
	Regex string `yaml:"regex" json:"regex"`
}

type ruleError struct {
	RuleName string `json:"rulename"`
	Err      string `json:"err"`
}

func (r *rules) load(path string) error {
	r.mu.Lock()
	defer r.mu.Unlock()

	rulesData, err := readFile(path)
	if err != nil {
		return err
	}

	err = yaml.Unmarshal(rulesData, &r)
	if err != nil {
		return err
	}

	_ = r.compileRegex(true)

	return nil
}

// Insert into map to prevent recompiling for every call
func (r *rules) compileRegex(storeInMap bool) []ruleError {
	errArr := []ruleError{}

	for _, rule := range r.Rules {
		compiled, err := regexp.Compile(rule.Value.Regex)
		if err != nil {
			log.Errorf("rule: %s, err: %s", rule.Name, err.Error())
			errArr = append(errArr, ruleError{RuleName: rule.Name, Err: err.Error()})
			// In the event of invalid regex, anything for that rule is allowed
			r.compiledRegexs[rule.Name] = defaultRegex
			// Store user supplied compiled regex if no error
		} else if storeInMap {
			// Update/Store in map
			r.compiledRegexs[rule.Name] = compiled
		}
	}

	// If any regex compilation errors detected, return
	if len(errArr) > 0 {
		return errArr
	}

	return nil
}

func (r *rules) validateAllRulesRegex() []ruleError {
	// To send back every rule that has invalid regex
	return r.compileRegex(false)
}

func (r *rules) ensureLabelsMatchRules(labels map[string]interface{}) error {
	for _, rule := range r.Rules {
		// Ensure labels contains rule
		if _, ok := labels[rule.Key]; !ok {
			// If rule is not found, reject
			errStr := fmt.Sprintf("%s not in labels", rule.Key)
			return errors.New(errStr)
		}

		// Force all values to strings to prevent panic from interface conversion
		labelVal := fmt.Sprintf("%s", labels[rule.Key])
		regex := r.compiledRegexs[rule.Name]

		if !regex.MatchString(labelVal) {
			errStr := fmt.Sprintf("Value for label '%s' does not match expression '%s'", rule.Key, rule.Value.Regex)
			return errors.New(errStr)
		}
	}

	return nil
}