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dyngeneric.go
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dyngeneric.go
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// Copyright 2022 Fortio Authors
package dflag
import (
"flag"
"fmt"
"strconv"
"strings"
"sync/atomic"
"time"
"golang.org/x/exp/constraints"
)
// DynamicFlagValue interface is a tag to know if a type is dynamic or not.
type DynamicFlagValue interface {
IsDynamicFlag() bool
}
// DynamicJSONFlagValue is a tag interface for JSON dynamic flags.
type DynamicJSONFlagValue interface {
IsJSON() bool
}
// DynamicFlagValueTag is a struct all dynamic flag inherit for marking they are dynamic.
type DynamicFlagValueTag struct{}
// IsDynamicFlag always returns true.
func (*DynamicFlagValueTag) IsDynamicFlag() bool {
return true
}
// A flag is dynamic if it implements DynamicFlagValue (which all the dyn* do)
// IsFlagDynamic returns whether the given Flag has been created in a Dynamic mode.
func IsFlagDynamic(f *flag.Flag) bool {
df, ok := f.Value.(DynamicFlagValue)
if !ok {
return false
}
return df.IsDynamicFlag() // will clearly return true if it exists
}
type DynamicBoolValueTag struct{}
func (*DynamicBoolValueTag) IsBoolFlag() bool {
return true
}
// ---- Generics section ---
type Set[T comparable] map[T]struct{}
// ValidateDynSetMinElements validates that the given Set has at least x elements.
func ValidateDynSetMinElements[T comparable](count int) func(Set[T]) error {
return func(value Set[T]) error {
if len(value) < count {
return fmt.Errorf("value set %+v must have at least %v elements", value, count)
}
return nil
}
}
// ValidateDynSliceMinElements validates that the given Set has at least x elements.
func ValidateDynSliceMinElements[T any](count int) func([]T) error {
return func(value []T) error {
if len(value) < count {
return fmt.Errorf("value slice %+v must have at least %v elements", value, count)
}
return nil
}
}
// DynValueTypes are the types currently supported by Parse[T] and thus by Dyn[T].
// DynJSON is special.
type DynValueTypes interface {
bool | time.Duration | float64 | int64 | string | []string | Set[string]
}
type DynValue[T any] struct {
DynamicFlagValueTag
av atomic.Value
flagName string
flagSet *flag.FlagSet
ready bool
syncNotifier bool
validator func(T) error
notifier func(oldValue T, newValue T)
mutator func(inp T) T
inpMutator func(inp string) string
}
func Dyn[T DynValueTypes](flagSet *flag.FlagSet, name string, value T, usage string) *DynValue[T] {
dynValue := DynValue[T]{}
dynInit(&dynValue, flagSet, name, value, usage)
flagSet.Var(&dynValue, name, usage)
flagSet.Lookup(name).DefValue = fmt.Sprintf("%v", value)
return &dynValue
}
func dynInit[T any](dynValue *DynValue[T], flagSet *flag.FlagSet, name string, value T, usage string) {
dynValue.flagName = name
dynValue.flagSet = flagSet
dynValue.av.Store(value)
dynValue.inpMutator = strings.TrimSpace // default so parsing of numbers etc works well
dynValue.ready = true
}
// Unfortunately IsBoolFlag isn't called, just presence is needed
// https://github.com/golang/go/issues/53473
/*
// lets the flag parsing know that -flagname is enough to turn to true.
func (d *DynValue[T]) IsBoolFlag() bool {
var v T
switch any(v).(type) {
case bool:
return true
default:
return false
}
}
*/
// Get retrieves the value in a thread-safe manner.
func (d *DynValue[T]) Get() T {
var zero T
if !d.ready {
// avoid crashing when String()->Get() is called by flagset.PrintDefaults
// which happens in error case (and is tested in nildptr_test.go)
return zero
}
return d.av.Load().(T)
}
// CommaStringToSlice converts a coma separated string to a slice.
func CommaStringToSlice(input string) []string {
// originally the heavy handed csv.NewReader(strings.NewReader(input)).Read()
return strings.Split(input, ",")
}
// Parse converts from string to our supported types (it's the beginning of the missing generics strconv.Parse[T]).
func Parse[T DynValueTypes](input string) (val T, err error) {
return parse[T](input)
}
func parse[T any](input string) (val T, err error) {
switch v := any(&val).(type) {
case *bool:
*v, err = strconv.ParseBool(input)
case *int64:
*v, err = strconv.ParseInt(strings.TrimSpace(input), 0, 64)
case *float64:
*v, err = strconv.ParseFloat(strings.TrimSpace(input), 64)
case *time.Duration:
*v, err = time.ParseDuration(input)
case *string:
*v = input
case *[]string:
*v = CommaStringToSlice(input)
case *Set[string]:
*v = SetFromSlice(CommaStringToSlice(input))
default:
// JSON Set() and thus Parse() is handled in dynjson.go
err = fmt.Errorf("unexpected type %T", val)
}
return
}
// SetFromSlice constructs a Set from a slice.
func SetFromSlice[T comparable](items []T) Set[T] {
res := map[T]struct{}{}
for _, item := range items {
res[item] = struct{}{}
}
return res
}
// Set updates the value from a string representation in a thread-safe manner.
// This operation may return an error if the provided `input` doesn't parse, or the resulting value doesn't pass an
// optional validator.
// If a notifier is set on the value, it will be invoked in a separate go-routine.
func (d *DynValue[T]) Set(rawInput string) error {
input := rawInput
if d.inpMutator != nil {
input = d.inpMutator(rawInput)
}
val, err := parse[T](input)
if err != nil {
return err
}
return d.PostSet(val)
}
func (d *DynValue[T]) PostSet(val T) error {
if d.mutator != nil {
val = d.mutator(val)
}
if d.validator != nil {
if err := d.validator(val); err != nil {
return err
}
}
oldVal := d.av.Swap(val).(T)
if d.notifier != nil {
if d.syncNotifier {
d.notifier(oldVal, val)
} else {
go d.notifier(oldVal, val)
}
}
return nil
}
// WithValidator adds a function that checks values before they're set.
// Any error returned by the validator will lead to the value being rejected.
// Validators are executed on the same go-routine as the call to `Set`.
func (d *DynValue[T]) WithValidator(validator func(T) error) *DynValue[T] {
d.validator = validator
return d
}
// WithNotifier adds a function is called every time a new value is successfully set.
// Each notifier is executed in a new go-routine.
func (d *DynValue[T]) WithNotifier(notifier func(oldValue T, newValue T)) *DynValue[T] {
d.notifier = notifier
return d
}
// WithSyncNotifier adds a function is called synchronously every time a new value is successfully set.
func (d *DynValue[T]) WithSyncNotifier(notifier func(oldValue T, newValue T)) *DynValue[T] {
d.notifier = notifier
d.syncNotifier = true
return d
}
// Type is an indicator of what this flag represents.
func (d *DynValue[T]) Type() string {
var v T
return fmt.Sprintf("dyn_%T", v)
}
// String returns the canonical string representation of the type.
func (d *DynValue[T]) String() string {
return fmt.Sprintf("%v", d.Get())
}
// WithValueMutator adds a function that changes the value of a flag as needed.
func (d *DynValue[T]) WithValueMutator(mutator func(inp T) T) *DynValue[T] {
d.mutator = mutator
return d
}
// WithInputMutator changes the default input string processing (TrimSpace).
func (d *DynValue[T]) WithInputMutator(mutator func(inp string) string) *DynValue[T] {
d.inpMutator = mutator
return d
}
// WithFileFlag adds an companion <name>_path flag that allows this value to be read from a file with dflag.ReadFileFlags.
//
// This is useful for reading large JSON files as flags. If the companion flag's value (whether default or overwritten)
// is set to empty string, nothing is read.
//
// Flag value reads are subject to notifiers and validators.
func (d *DynValue[T]) WithFileFlag(defaultPath string) (*DynValue[T], *FileReadValue) {
return d, FileReadFlag(d.flagSet, d.flagName, defaultPath)
}
// ValidateRange returns a validator that checks if the value is in the given range.
func ValidateRange[T constraints.Ordered](fromInclusive T, toInclusive T) func(T) error {
return func(value T) error {
if value > toInclusive || value < fromInclusive {
return fmt.Errorf("value %v not in [%v, %v] range", value, fromInclusive, toInclusive)
}
return nil
}
}