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selector.go
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selector.go
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/*
Copyright 2014 The Kubernetes Authors 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 (
"bytes"
"fmt"
"sort"
"strings"
"k8s.io/kubernetes/pkg/util/fielderrors"
"k8s.io/kubernetes/pkg/util/sets"
"k8s.io/kubernetes/pkg/util/validation"
)
// Selector represents a label selector.
type Selector interface {
// Matches returns true if this selector matches the given set of labels.
Matches(Labels) bool
// Empty returns true if this selector does not restrict the selection space.
Empty() bool
// String returns a human readable string that represents this selector.
String() string
// Add add a specific requirement for the selector
Add(key string, operator Operator, values []string) Selector
}
// Everything returns a selector that matches all labels.
func Everything() Selector {
return LabelSelector{}
}
type nothingSelector struct{}
func (n nothingSelector) Matches(_ Labels) bool { return false }
func (n nothingSelector) Empty() bool { return false }
func (n nothingSelector) String() string { return "<null>" }
func (n nothingSelector) Add(_ string, _ Operator, _ []string) Selector { return n }
// Nothing returns a selector that matches no labels
func Nothing() Selector {
return nothingSelector{}
}
// Operator represents a key's relationship
// to a set of values in a Requirement.
type Operator string
const (
DoesNotExistOperator Operator = "!"
EqualsOperator Operator = "="
DoubleEqualsOperator Operator = "=="
InOperator Operator = "in"
NotEqualsOperator Operator = "!="
NotInOperator Operator = "notin"
ExistsOperator Operator = "exists"
)
//LabelSelector is a list of Requirements.
type LabelSelector []Requirement
// Sort by obtain determisitic parser
type ByKey []Requirement
func (a ByKey) Len() int { return len(a) }
func (a ByKey) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func (a ByKey) Less(i, j int) bool { return a[i].key < a[j].key }
// Requirement is a selector that contains values, a key
// and an operator that relates the key and values. The zero
// value of Requirement is invalid.
// Requirement implements both set based match and exact match
// Requirement is initialized via NewRequirement constructor for creating a valid Requirement.
type Requirement struct {
key string
operator Operator
strValues sets.String
}
// NewRequirement is the constructor for a Requirement.
// If any of these rules is violated, an error is returned:
// (1) The operator can only be In, NotIn, Equals, DoubleEquals, NotEquals, Exists, or DoesNotExist.
// (2) If the operator is In or NotIn, the values set must be non-empty.
// (3) If the operator is Equals, DoubleEquals, or NotEquals, the values set must contain one value.
// (4) If the operator is Exists or DoesNotExist, the value set must be empty.
// (5) The key is invalid due to its length, or sequence
// of characters. See validateLabelKey for more details.
//
// The empty string is a valid value in the input values set.
func NewRequirement(key string, op Operator, vals sets.String) (*Requirement, error) {
if err := validateLabelKey(key); err != nil {
return nil, err
}
switch op {
case InOperator, NotInOperator:
if len(vals) == 0 {
return nil, fmt.Errorf("for 'in', 'notin' operators, values set can't be empty")
}
case EqualsOperator, DoubleEqualsOperator, NotEqualsOperator:
if len(vals) != 1 {
return nil, fmt.Errorf("exact-match compatibility requires one single value")
}
case ExistsOperator, DoesNotExistOperator:
if len(vals) != 0 {
return nil, fmt.Errorf("values set must be empty for exists and does not exist")
}
default:
return nil, fmt.Errorf("operator '%v' is not recognized", op)
}
for v := range vals {
if err := validateLabelValue(v); err != nil {
return nil, err
}
}
return &Requirement{key: key, operator: op, strValues: vals}, nil
}
// Matches returns true if the Requirement matches the input Labels.
// There is a match in the following cases:
// (1) The operator is Exists and Labels has the Requirement's key.
// (2) The operator is In, Labels has the Requirement's key and Labels'
// value for that key is in Requirement's value set.
// (3) The operator is NotIn, Labels has the Requirement's key and
// Labels' value for that key is not in Requirement's value set.
// (4) The operator is DoesNotExist or NotIn and Labels does not have the
// Requirement's key.
func (r *Requirement) Matches(ls Labels) bool {
switch r.operator {
case InOperator, EqualsOperator, DoubleEqualsOperator:
if !ls.Has(r.key) {
return false
}
return r.strValues.Has(ls.Get(r.key))
case NotInOperator, NotEqualsOperator:
if !ls.Has(r.key) {
return true
}
return !r.strValues.Has(ls.Get(r.key))
case ExistsOperator:
return ls.Has(r.key)
case DoesNotExistOperator:
return !ls.Has(r.key)
default:
return false
}
}
// Return true if the LabelSelector doesn't restrict selection space
func (lsel LabelSelector) Empty() bool {
if lsel == nil {
return true
}
return len(lsel) == 0
}
// String returns a human-readable string that represents this
// Requirement. If called on an invalid Requirement, an error is
// returned. See NewRequirement for creating a valid Requirement.
func (r *Requirement) String() string {
var buffer bytes.Buffer
if r.operator == DoesNotExistOperator {
buffer.WriteString("!")
}
buffer.WriteString(r.key)
switch r.operator {
case EqualsOperator:
buffer.WriteString("=")
case DoubleEqualsOperator:
buffer.WriteString("==")
case NotEqualsOperator:
buffer.WriteString("!=")
case InOperator:
buffer.WriteString(" in ")
case NotInOperator:
buffer.WriteString(" notin ")
case ExistsOperator, DoesNotExistOperator:
return buffer.String()
}
switch r.operator {
case InOperator, NotInOperator:
buffer.WriteString("(")
}
if len(r.strValues) == 1 {
buffer.WriteString(r.strValues.List()[0])
} else { // only > 1 since == 0 prohibited by NewRequirement
buffer.WriteString(strings.Join(r.strValues.List(), ","))
}
switch r.operator {
case InOperator, NotInOperator:
buffer.WriteString(")")
}
return buffer.String()
}
// Add adds a requirement to the selector. It copies the current selector returning a new one
func (lsel LabelSelector) Add(key string, operator Operator, values []string) Selector {
var reqs []Requirement
for _, item := range lsel {
reqs = append(reqs, item)
}
if r, err := NewRequirement(key, operator, sets.NewString(values...)); err == nil {
reqs = append(reqs, *r)
}
return LabelSelector(reqs)
}
// Matches for a LabelSelector returns true if all
// its Requirements match the input Labels. If any
// Requirement does not match, false is returned.
func (lsel LabelSelector) Matches(l Labels) bool {
for _, req := range lsel {
if matches := req.Matches(l); !matches {
return false
}
}
return true
}
// String returns a comma-separated string of all
// the LabelSelector Requirements' human-readable strings.
func (lsel LabelSelector) String() string {
var reqs []string
for _, req := range lsel {
reqs = append(reqs, req.String())
}
return strings.Join(reqs, ",")
}
// constants definition for lexer token
type Token int
const (
ErrorToken Token = iota
EndOfStringToken
ClosedParToken
CommaToken
DoesNotExistToken
DoubleEqualsToken
EqualsToken
IdentifierToken // to represent keys and values
InToken
NotEqualsToken
NotInToken
OpenParToken
)
// string2token contains the mapping between lexer Token and token literal
// (except IdentifierToken, EndOfStringToken and ErrorToken since it makes no sense)
var string2token = map[string]Token{
")": ClosedParToken,
",": CommaToken,
"!": DoesNotExistToken,
"==": DoubleEqualsToken,
"=": EqualsToken,
"in": InToken,
"!=": NotEqualsToken,
"notin": NotInToken,
"(": OpenParToken,
}
// The item produced by the lexer. It contains the Token and the literal.
type ScannedItem struct {
tok Token
literal string
}
// isWhitespace returns true if the rune is a space, tab, or newline.
func isWhitespace(ch byte) bool {
return ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n'
}
// isSpecialSymbol detect if the character ch can be an operator
func isSpecialSymbol(ch byte) bool {
switch ch {
case '=', '!', '(', ')', ',':
return true
}
return false
}
// Lexer represents the Lexer struct for label selector.
// It contains necessary informationt to tokenize the input string
type Lexer struct {
// s stores the string to be tokenized
s string
// pos is the position currently tokenized
pos int
}
// read return the character currently lexed
// increment the position and check the buffer overflow
func (l *Lexer) read() (b byte) {
b = 0
if l.pos < len(l.s) {
b = l.s[l.pos]
l.pos++
}
return b
}
// unread 'undoes' the last read character
func (l *Lexer) unread() {
l.pos--
}
// scanIdOrKeyword scans string to recognize literal token (for example 'in') or an identifier.
func (l *Lexer) scanIdOrKeyword() (tok Token, lit string) {
var buffer []byte
IdentifierLoop:
for {
switch ch := l.read(); {
case ch == 0:
break IdentifierLoop
case isSpecialSymbol(ch) || isWhitespace(ch):
l.unread()
break IdentifierLoop
default:
buffer = append(buffer, ch)
}
}
s := string(buffer)
if val, ok := string2token[s]; ok { // is a literal token?
return val, s
}
return IdentifierToken, s // otherwise is an identifier
}
// scanSpecialSymbol scans string starting with special symbol.
// special symbol identify non literal operators. "!=", "==", "="
func (l *Lexer) scanSpecialSymbol() (Token, string) {
lastScannedItem := ScannedItem{}
var buffer []byte
SpecialSymbolLoop:
for {
switch ch := l.read(); {
case ch == 0:
break SpecialSymbolLoop
case isSpecialSymbol(ch):
buffer = append(buffer, ch)
if token, ok := string2token[string(buffer)]; ok {
lastScannedItem = ScannedItem{tok: token, literal: string(buffer)}
} else if lastScannedItem.tok != 0 {
l.unread()
break SpecialSymbolLoop
}
default:
l.unread()
break SpecialSymbolLoop
}
}
if lastScannedItem.tok == 0 {
return ErrorToken, fmt.Sprintf("error expected: keyword found '%s'", buffer)
}
return lastScannedItem.tok, lastScannedItem.literal
}
// skipWhiteSpaces consumes all blank characters
// returning the first non blank character
func (l *Lexer) skipWhiteSpaces(ch byte) byte {
for {
if !isWhitespace(ch) {
return ch
}
ch = l.read()
}
}
// Lex returns a pair of Token and the literal
// literal is meaningfull only for IdentifierToken token
func (l *Lexer) Lex() (tok Token, lit string) {
switch ch := l.skipWhiteSpaces(l.read()); {
case ch == 0:
return EndOfStringToken, ""
case isSpecialSymbol(ch):
l.unread()
return l.scanSpecialSymbol()
default:
l.unread()
return l.scanIdOrKeyword()
}
}
// Parser data structure contains the label selector parser data strucutre
type Parser struct {
l *Lexer
scannedItems []ScannedItem
position int
}
// Parser context represents context during parsing:
// some literal for example 'in' and 'notin' can be
// recognized as operator for example 'x in (a)' but
// it can be recognized as value for example 'value in (in)'
type ParserContext int
const (
KeyAndOperator ParserContext = iota
Values
)
// lookahead func returns the current token and string. No increment of current position
func (p *Parser) lookahead(context ParserContext) (Token, string) {
tok, lit := p.scannedItems[p.position].tok, p.scannedItems[p.position].literal
if context == Values {
switch tok {
case InToken, NotInToken:
tok = IdentifierToken
}
}
return tok, lit
}
// consume returns current token and string. Increments the the position
func (p *Parser) consume(context ParserContext) (Token, string) {
p.position++
tok, lit := p.scannedItems[p.position-1].tok, p.scannedItems[p.position-1].literal
if context == Values {
switch tok {
case InToken, NotInToken:
tok = IdentifierToken
}
}
return tok, lit
}
// scan runs through the input string and stores the ScannedItem in an array
// Parser can now lookahead and consume the tokens
func (p *Parser) scan() {
for {
token, literal := p.l.Lex()
p.scannedItems = append(p.scannedItems, ScannedItem{token, literal})
if token == EndOfStringToken {
break
}
}
}
// parse runs the left recursive descending algorithm
// on input string. It returns a list of Requirement objects.
func (p *Parser) parse() ([]Requirement, error) {
p.scan() // init scannedItems
var requirements []Requirement
for {
tok, lit := p.lookahead(Values)
switch tok {
case IdentifierToken, DoesNotExistToken:
r, err := p.parseRequirement()
if err != nil {
return nil, fmt.Errorf("unable to parse requirement: %v", err)
}
requirements = append(requirements, *r)
t, l := p.consume(Values)
switch t {
case EndOfStringToken:
return requirements, nil
case CommaToken:
t2, l2 := p.lookahead(Values)
if t2 != IdentifierToken && t2 != DoesNotExistToken {
return nil, fmt.Errorf("found '%s', expected: identifier after ','", l2)
}
default:
return nil, fmt.Errorf("found '%s', expected: ',' or 'end of string'", l)
}
case EndOfStringToken:
return requirements, nil
default:
return nil, fmt.Errorf("found '%s', expected: !, identifier, or 'end of string'", lit)
}
}
}
func (p *Parser) parseRequirement() (*Requirement, error) {
key, operator, err := p.parseKeyAndInferOperator()
if err != nil {
return nil, err
}
if operator == ExistsOperator || operator == DoesNotExistOperator { // operator found lookahead set checked
return NewRequirement(key, operator, nil)
}
operator, err = p.parseOperator()
if err != nil {
return nil, err
}
var values sets.String
switch operator {
case InOperator, NotInOperator:
values, err = p.parseValues()
case EqualsOperator, DoubleEqualsOperator, NotEqualsOperator:
values, err = p.parseExactValue()
}
if err != nil {
return nil, err
}
return NewRequirement(key, operator, values)
}
// parseKeyAndInferOperator parse literals.
// in case of no operator '!, in, notin, ==, =, !=' are found
// the 'exists' operator is inferred
func (p *Parser) parseKeyAndInferOperator() (string, Operator, error) {
var operator Operator
tok, literal := p.consume(Values)
if tok == DoesNotExistToken {
operator = DoesNotExistOperator
tok, literal = p.consume(Values)
}
if tok != IdentifierToken {
err := fmt.Errorf("found '%s', expected: identifier", literal)
return "", "", err
}
if err := validateLabelKey(literal); err != nil {
return "", "", err
}
if t, _ := p.lookahead(Values); t == EndOfStringToken || t == CommaToken {
if operator != DoesNotExistOperator {
operator = ExistsOperator
}
}
return literal, operator, nil
}
// parseOperator return operator and eventually matchType
// matchType can be exact
func (p *Parser) parseOperator() (op Operator, err error) {
tok, lit := p.consume(KeyAndOperator)
switch tok {
// DoesNotExistToken shouldn't be here because it's a unary operator, not a binary operator
case InToken:
op = InOperator
case EqualsToken:
op = EqualsOperator
case DoubleEqualsToken:
op = DoubleEqualsOperator
case NotInToken:
op = NotInOperator
case NotEqualsToken:
op = NotEqualsOperator
default:
return "", fmt.Errorf("found '%s', expected: '=', '!=', '==', 'in', notin'", lit)
}
return op, nil
}
// parseValues parses the values for set based matching (x,y,z)
func (p *Parser) parseValues() (sets.String, error) {
tok, lit := p.consume(Values)
if tok != OpenParToken {
return nil, fmt.Errorf("found '%s' expected: '('", lit)
}
tok, lit = p.lookahead(Values)
switch tok {
case IdentifierToken, CommaToken:
s, err := p.parseIdentifiersList() // handles general cases
if err != nil {
return s, err
}
if tok, _ = p.consume(Values); tok != ClosedParToken {
return nil, fmt.Errorf("found '%s', expected: ')'", lit)
}
return s, nil
case ClosedParToken: // handles "()"
p.consume(Values)
return sets.NewString(""), nil
default:
return nil, fmt.Errorf("found '%s', expected: ',', ')' or identifier", lit)
}
}
// parseIdentifiersList parses a (possibly empty) list of
// of comma separated (possibly empty) identifiers
func (p *Parser) parseIdentifiersList() (sets.String, error) {
s := sets.NewString()
for {
tok, lit := p.consume(Values)
switch tok {
case IdentifierToken:
s.Insert(lit)
tok2, lit2 := p.lookahead(Values)
switch tok2 {
case CommaToken:
continue
case ClosedParToken:
return s, nil
default:
return nil, fmt.Errorf("found '%s', expected: ',' or ')'", lit2)
}
case CommaToken: // handled here since we can have "(,"
if s.Len() == 0 {
s.Insert("") // to handle (,
}
tok2, _ := p.lookahead(Values)
if tok2 == ClosedParToken {
s.Insert("") // to handle ,) Double "" removed by StringSet
return s, nil
}
if tok2 == CommaToken {
p.consume(Values)
s.Insert("") // to handle ,, Double "" removed by StringSet
}
default: // it can be operator
return s, fmt.Errorf("found '%s', expected: ',', or identifier", lit)
}
}
}
// parseExactValue parses the only value for exact match style
func (p *Parser) parseExactValue() (sets.String, error) {
s := sets.NewString()
tok, lit := p.lookahead(Values)
if tok == EndOfStringToken || tok == CommaToken {
s.Insert("")
return s, nil
}
tok, lit = p.consume(Values)
if tok == IdentifierToken {
s.Insert(lit)
return s, nil
}
return nil, fmt.Errorf("found '%s', expected: identifier", lit)
}
// Parse takes a string representing a selector and returns a selector
// object, or an error. This parsing function differs from ParseSelector
// as they parse different selectors with different syntaxes.
// The input will cause an error if it does not follow this form:
//
// <selector-syntax> ::= <requirement> | <requirement> "," <selector-syntax> ]
// <requirement> ::= [!] KEY [ <set-based-restriction> | <exact-match-restriction> ]
// <set-based-restriction> ::= "" | <inclusion-exclusion> <value-set>
// <inclusion-exclusion> ::= <inclusion> | <exclusion>
// <exclusion> ::= "notin"
// <inclusion> ::= "in"
// <value-set> ::= "(" <values> ")"
// <values> ::= VALUE | VALUE "," <values>
// <exact-match-restriction> ::= ["="|"=="|"!="] VALUE
// KEY is a sequence of one or more characters following [ DNS_SUBDOMAIN "/" ] DNS_LABEL
// VALUE is a sequence of zero or more characters "([A-Za-z0-9_-\.])". Max length is 64 character.
// Delimiter is white space: (' ', '\t')
// Example of valid syntax:
// "x in (foo,,baz),y,z notin ()"
//
// Note:
// (1) Inclusion - " in " - denotes that the KEY exists and is equal to any of the
// VALUEs in its requirement
// (2) Exclusion - " notin " - denotes that the KEY is not equal to any
// of the VALUEs in its requirement or does not exist
// (3) The empty string is a valid VALUE
// (4) A requirement with just a KEY - as in "y" above - denotes that
// the KEY exists and can be any VALUE.
// (5) A requirement with just !KEY requires that the KEY not exist.
//
func Parse(selector string) (Selector, error) {
p := &Parser{l: &Lexer{s: selector, pos: 0}}
items, error := p.parse()
if error == nil {
sort.Sort(ByKey(items)) // sort to grant determistic parsing
return LabelSelector(items), error
}
return nil, error
}
const qualifiedNameErrorMsg string = "must match regex [" + validation.DNS1123SubdomainFmt + " / ] " + validation.DNS1123LabelFmt
func validateLabelKey(k string) error {
if !validation.IsQualifiedName(k) {
return fielderrors.NewFieldInvalid("label key", k, qualifiedNameErrorMsg)
}
return nil
}
func validateLabelValue(v string) error {
if !validation.IsValidLabelValue(v) {
return fielderrors.NewFieldInvalid("label value", v, qualifiedNameErrorMsg)
}
return nil
}
// SelectorFromSet returns a Selector which will match exactly the given Set. A
// nil and empty Sets are considered equivalent to Everything().
func SelectorFromSet(ls Set) Selector {
if ls == nil {
return LabelSelector{}
}
var requirements []Requirement
for label, value := range ls {
if r, err := NewRequirement(label, EqualsOperator, sets.NewString(value)); err != nil {
//TODO: double check errors when input comes from serialization?
return LabelSelector{}
} else {
requirements = append(requirements, *r)
}
}
return LabelSelector(requirements)
}