k3s/pkg/labels/query.go

/*
Copyright 2014 Google Inc. 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 labels

import (
	"fmt"
	"strings"
)

// Represents a label query.
type Query interface {
	// Returns true if this query matches the given set of labels.
	Matches(Labels) bool

	// Prints a human readable version of this label query.
	String() string
}

// Everything returns a query that matches all labels.
func Everything() Query {
	return andTerm{}
}

type hasTerm struct {
	label, value string
}

func (t *hasTerm) Matches(ls Labels) bool {
	return ls.Get(t.label) == t.value
}

func (t *hasTerm) String() string {
	return fmt.Sprintf("%v=%v", t.label, t.value)
}

type notHasTerm struct {
	label, value string
}

func (t *notHasTerm) Matches(ls Labels) bool {
	return ls.Get(t.label) != t.value
}

func (t *notHasTerm) String() string {
	return fmt.Sprintf("%v!=%v", t.label, t.value)
}

type andTerm []Query

func (t andTerm) Matches(ls Labels) bool {
	for _, q := range t {
		if !q.Matches(ls) {
			return false
		}
	}
	return true
}

func (t andTerm) String() string {
	var terms []string
	for _, q := range t {
		terms = append(terms, q.String())
	}
	return strings.Join(terms, ",")
}

func try(queryPiece, op string) (lhs, rhs string, ok bool) {
	pieces := strings.Split(queryPiece, op)
	if len(pieces) == 2 {
		return pieces[0], pieces[1], true
	}
	return "", "", false
}

// Given a Set, return a Query which will match exactly that Set.
func QueryFromSet(ls Set) Query {
	var items []Query
	for label, value := range ls {
		items = append(items, &hasTerm{label: label, value: value})
	}
	if len(items) == 1 {
		return items[0]
	}
	return andTerm(items)
}

// Takes a string repsenting a label query and returns an object suitable for matching, or an error.
func ParseQuery(query string) (Query, error) {
	parts := strings.Split(query, ",")
	var items []Query
	for _, part := range parts {
		if part == "" {
			continue
		}
		if lhs, rhs, ok := try(part, "!="); ok {
			items = append(items, &notHasTerm{label: lhs, value: rhs})
		} else if lhs, rhs, ok := try(part, "=="); ok {
			items = append(items, &hasTerm{label: lhs, value: rhs})
		} else if lhs, rhs, ok := try(part, "="); ok {
			items = append(items, &hasTerm{label: lhs, value: rhs})
		} else {
			return nil, fmt.Errorf("invalid label query: '%s'; can't understand '%s'", query, part)
		}
	}
	if len(items) == 1 {
		return items[0], nil
	}
	return andTerm(items), nil
}