/
leakybucket.go
133 lines (112 loc) · 3.27 KB
/
leakybucket.go
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package ratelimit
import (
"context"
"fmt"
"net/http"
"strconv"
"time"
"github.com/zalando/skipper/eskip"
"github.com/zalando/skipper/filters"
"github.com/zalando/skipper/ratelimit"
)
type leakyBucket interface {
Add(ctx context.Context, label string, increment int) (added bool, retry time.Duration, err error)
}
type leakyBucketSpec struct {
create func(capacity int, emission time.Duration) leakyBucket
}
type leakyBucketFilter struct {
label *eskip.Template
bucket leakyBucket
increment int
failClosed bool
}
// NewClusterLeakyBucketRatelimit creates a filter Spec, whose instances implement rate limiting using leaky bucket algorithm.
//
// The leaky bucket is an algorithm based on an analogy of how a bucket with a constant leak will overflow if either
// the average rate at which water is poured in exceeds the rate at which the bucket leaks or if more water than
// the capacity of the bucket is poured in all at once.
// See https://en.wikipedia.org/wiki/Leaky_bucket
//
// Example to allow each unique Authorization header once in five seconds:
//
// clusterLeakyBucketRatelimit("auth-${request.header.Authorization}", 1, "5s", 2, 1)
func NewClusterLeakyBucketRatelimit(registry *ratelimit.Registry) filters.Spec {
return &leakyBucketSpec{
create: func(capacity int, emission time.Duration) leakyBucket {
return ratelimit.NewClusterLeakyBucket(registry, capacity, emission)
},
}
}
func (s *leakyBucketSpec) Name() string {
return filters.ClusterLeakyBucketRatelimitName
}
func (s *leakyBucketSpec) CreateFilter(args []interface{}) (filters.Filter, error) {
if len(args) != 5 {
return nil, filters.ErrInvalidFilterParameters
}
label, ok := args[0].(string)
if !ok {
return nil, filters.ErrInvalidFilterParameters
}
leakVolume, err := natural(args[1])
if err != nil {
return nil, err
}
leakPeriod, err := getDurationArg(args[2])
if err != nil {
return nil, err
}
if leakPeriod <= 0 {
return nil, filters.ErrInvalidFilterParameters
}
capacity, err := natural(args[3])
if err != nil {
return nil, err
}
increment, err := natural(args[4])
if err != nil {
return nil, err
}
// emission is the reciprocal of the leak rate
emission := leakPeriod / time.Duration(leakVolume)
return &leakyBucketFilter{
label: eskip.NewTemplate(label),
bucket: s.create(capacity, emission),
increment: increment,
}, nil
}
func fail(ctx filters.FilterContext, header http.Header) {
ctx.Serve(&http.Response{StatusCode: http.StatusTooManyRequests, Header: header})
}
func (f *leakyBucketFilter) Request(ctx filters.FilterContext) {
label, ok := f.label.ApplyContext(ctx)
if !ok {
return // allow on missing placeholders
}
added, retry, err := f.bucket.Add(ctx.Request().Context(), label, f.increment)
if err != nil {
if f.failClosed {
header := http.Header{}
header.Set("Retry-After", "60")
fail(ctx, header)
}
return
}
if added {
return // allow if successfully added
}
header := http.Header{}
if retry > 0 {
header.Set("Retry-After", strconv.Itoa(int(retry/time.Second)))
}
fail(ctx, header)
}
func (*leakyBucketFilter) Response(filters.FilterContext) {}
func natural(arg interface{}) (n int, err error) {
n, err = getIntArg(arg)
if err == nil && n <= 0 {
err = fmt.Errorf(`number %d must be positive`, n)
}
return
}