154 lines
3.5 KiB
Go
154 lines
3.5 KiB
Go
package doorman
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import (
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"encoding/json"
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"errors"
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"log"
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"math"
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mathrand "math/rand"
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"net/http"
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"sync"
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"time"
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"github.com/dchest/siphash"
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"github.com/didiercrunch/doorman/shared"
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"gopkg.in/mgo.v2/bson"
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)
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// the smallest value that makes two floats the same. Consequently x == y
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// if |x - y| < epsilon. It is a known issue that one can find three numbers
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// a,b,c such that a == b, b == c and a != c. Hence, it is the programmer role
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// to be very careful about equalities and inequalities.
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const epsilon float64 = 0.000000001
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var rand *mathrand.Rand
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func initRandomSeed() {
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kindOfRandomSeed := mathrand.NewSource(time.Now().Unix())
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rand = mathrand.New(kindOfRandomSeed)
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}
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func init() {
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initRandomSeed()
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}
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func IsZero(f float64) bool {
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if math.Abs(f) > epsilon {
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return false
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}
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return true
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}
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func IsEqual(f1, f2 float64) bool {
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return IsZero(f1 - f2)
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}
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type Doorman struct {
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Id bson.ObjectId // the id of the doorman
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LastChangeTimestamp int64 // an always increasing int that represent the last time the doorman has beed updated
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Probabilities []float64 // The probability of each cases. The sum of probabilities needs to be one
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wg sync.WaitGroup // waitgroup for goroutine safety
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}
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func NewDoorman(id bson.ObjectId, Probabilities []float64) *Doorman {
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wab := &Doorman{}
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wab.Id = id
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wab.Probabilities = Probabilities
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return wab
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}
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func (w *Doorman) Length() int {
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return len(w.Probabilities)
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}
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func (w *Doorman) UpdateHard(baseURL string) error {
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r, err := http.Get(baseURL + "/" + w.Id.Hex())
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if err != nil {
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return err
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}
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message := new(shared.DoormanUpdater)
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d := json.NewDecoder(r.Body)
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if err := d.Decode(message); err != nil {
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return err
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} else {
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return w.Update(message)
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}
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}
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func (w *Doorman) Update(wu *shared.DoormanUpdater) error {
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if wu.Timestamp <= w.LastChangeTimestamp {
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return nil
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}
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if wu.Id != w.Id.Hex() {
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return errors.New("bad doorman id")
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}
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w.wg.Add(1)
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defer w.wg.Done()
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w.LastChangeTimestamp = wu.Timestamp
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if !IsEqual(w.sum(wu.Probabilities), 1) {
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return errors.New("the sum of probabilities cannot be different than 1")
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}
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w.Probabilities = wu.Probabilities
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log.Printf("Updated doorman %v with new probabilities %v with timestamp %v", wu.Id, wu.Probabilities, wu.Timestamp)
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return nil
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}
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func (w *Doorman) sum(prob []float64) float64 {
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var ret float64 = 0
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for _, p := range prob {
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ret += p
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}
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return ret
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}
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func (w *Doorman) Validate() error {
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if len(w.Probabilities) == 0 {
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return errors.New("not initiated")
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}
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if !IsZero(w.sum(w.Probabilities) - 1.0) {
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return errors.New("The sum of probabilities is not one")
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}
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return nil
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}
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func (w *Doorman) GetCase(choosenRandomPosition float64) uint {
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w.wg.Wait()
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var prob float64 = 0
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for i, p := range w.Probabilities {
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prob += p
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if choosenRandomPosition-epsilon < prob {
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return uint(i)
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}
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}
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panic("cannot have a probability above 1")
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}
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func (w *Doorman) GenerateRandomProbabilityFromInteger(data uint64) float64 {
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var ret float64 = 0
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for i := 0; data > 0; i++ {
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if data&1 == 1 {
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ret += 1.0 / math.Pow(2, float64(i+1))
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}
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data >>= 1
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}
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return ret
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}
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func (w *Doorman) Hash(data ...[]byte) uint64 {
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h := siphash.New(make([]byte, 16))
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for _, datum := range data {
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h.Write(datum)
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}
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return h.Sum64()
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}
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func (w *Doorman) GetCaseFromData(data ...[]byte) uint {
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random := w.GenerateRandomProbabilityFromInteger(w.Hash(data...))
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return w.GetCase(random)
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}
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func (w *Doorman) GetRandomCase() uint {
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return w.GetCase(rand.Float64())
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}
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