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// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package label
import (
"fmt"
"io"
"reflect"
"unsafe"
)
// Key is used as the identity of a Label.
// Keys are intended to be compared by pointer only, the name should be unique
// for communicating with external systems, but it is not required or enforced.
type Key interface {
// Name returns the key name.
Name() string
// Description returns a string that can be used to describe the value.
Description() string
// Format is used in formatting to append the value of the label to the
// supplied buffer.
// The formatter may use the supplied buf as a scratch area to avoid
// allocations.
Format(w io.Writer, buf []byte, l Label)
}
// Label holds a key and value pair.
// It is normally used when passing around lists of labels.
type Label struct {
key Key
packed uint64
untyped interface{}
}
// Map is the interface to a collection of Labels indexed by key.
type Map interface {
// Find returns the label that matches the supplied key.
Find(key Key) Label
}
// List is the interface to something that provides an iterable
// list of labels.
// Iteration should start from 0 and continue until Valid returns false.
type List interface {
// Valid returns true if the index is within range for the list.
// It does not imply the label at that index will itself be valid.
Valid(index int) bool
// Label returns the label at the given index.
Label(index int) Label
}
// list implements LabelList for a list of Labels.
type list struct {
labels []Label
}
// filter wraps a LabelList filtering out specific labels.
type filter struct {
keys []Key
underlying List
}
// listMap implements LabelMap for a simple list of labels.
type listMap struct {
labels []Label
}
// mapChain implements LabelMap for a list of underlying LabelMap.
type mapChain struct {
maps []Map
}
// OfValue creates a new label from the key and value.
// This method is for implementing new key types, label creation should
// normally be done with the Of method of the key.
func OfValue(k Key, value interface{}) Label { return Label{key: k, untyped: value} }
// UnpackValue assumes the label was built using LabelOfValue and returns the value
// that was passed to that constructor.
// This method is for implementing new key types, for type safety normal
// access should be done with the From method of the key.
func (t Label) UnpackValue() interface{} { return t.untyped }
// Of64 creates a new label from a key and a uint64. This is often
// used for non uint64 values that can be packed into a uint64.
// This method is for implementing new key types, label creation should
// normally be done with the Of method of the key.
func Of64(k Key, v uint64) Label { return Label{key: k, packed: v} }
// Unpack64 assumes the label was built using LabelOf64 and returns the value that
// was passed to that constructor.
// This method is for implementing new key types, for type safety normal
// access should be done with the From method of the key.
func (t Label) Unpack64() uint64 { return t.packed }
// OfString creates a new label from a key and a string.
// This method is for implementing new key types, label creation should
// normally be done with the Of method of the key.
func OfString(k Key, v string) Label {
hdr := (*reflect.StringHeader)(unsafe.Pointer(&v))
return Label{
key: k,
packed: uint64(hdr.Len),
untyped: unsafe.Pointer(hdr.Data),
}
}
// UnpackString assumes the label was built using LabelOfString and returns the
// value that was passed to that constructor.
// This method is for implementing new key types, for type safety normal
// access should be done with the From method of the key.
func (t Label) UnpackString() string {
var v string
hdr := (*reflect.StringHeader)(unsafe.Pointer(&v))
hdr.Data = uintptr(t.untyped.(unsafe.Pointer))
hdr.Len = int(t.packed)
return *(*string)(unsafe.Pointer(hdr))
}
// Valid returns true if the Label is a valid one (it has a key).
func (t Label) Valid() bool { return t.key != nil }
// Key returns the key of this Label.
func (t Label) Key() Key { return t.key }
// Format is used for debug printing of labels.
func (t Label) Format(f fmt.State, r rune) {
if !t.Valid() {
io.WriteString(f, `nil`)
return
}
io.WriteString(f, t.Key().Name())
io.WriteString(f, "=")
var buf [128]byte
t.Key().Format(f, buf[:0], t)
}
func (l *list) Valid(index int) bool {
return index >= 0 && index < len(l.labels)
}
func (l *list) Label(index int) Label {
return l.labels[index]
}
func (f *filter) Valid(index int) bool {
return f.underlying.Valid(index)
}
func (f *filter) Label(index int) Label {
l := f.underlying.Label(index)
for _, f := range f.keys {
if l.Key() == f {
return Label{}
}
}
return l
}
func (lm listMap) Find(key Key) Label {
for _, l := range lm.labels {
if l.Key() == key {
return l
}
}
return Label{}
}
func (c mapChain) Find(key Key) Label {
for _, src := range c.maps {
l := src.Find(key)
if l.Valid() {
return l
}
}
return Label{}
}
var emptyList = &list{}
func NewList(labels ...Label) List {
if len(labels) == 0 {
return emptyList
}
return &list{labels: labels}
}
func Filter(l List, keys ...Key) List {
if len(keys) == 0 {
return l
}
return &filter{keys: keys, underlying: l}
}
func NewMap(labels ...Label) Map {
return listMap{labels: labels}
}
func MergeMaps(srcs ...Map) Map {
var nonNil []Map
for _, src := range srcs {
if src != nil {
nonNil = append(nonNil, src)
}
}
if len(nonNil) == 1 {
return nonNil[0]
}
return mapChain{maps: nonNil}
}
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