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adds middleware for rate limiting (#1724)
* adds middleware for rate limiting

* added comment for InMemoryStore ShouldAllow

* removed redundant mutex declaration

* fixed lint issues

* removed sleep from tests

* improved coverage

* refactor: renames Identifiers, includes default SourceFunc

* Added last seen stats for visitor

* uses http Constants for improved readdability
adds default error handler

* used other handler apart from default handler to mark custom error handler for rate limiting

* split tests into separate blocks
added an error pair to IdentifierExtractor
Includes deny handler for explicitly denying requests

* adds comments for exported members Extractor and ErrorHandler

* makes cleanup implementation inhouse

* Avoid race for cleanup due to non-atomic access to store.expiresIn

* Use a dedicated producer for rate testing

* tidy commit

* refactors tests, implicitly tests lastSeen property on visitor
switches NewRateLimiterMemoryStore constructor to Referential Functions style (Advised by @pafuent)

* switches to mock of time module for time based tests
tests are now fully deterministic

* improved coverage

* replaces Rob Pike referential options with more conventional struct configs
makes cleanup asynchronous

* blocks racy access to lastCleanup

* Add benchmark tests for rate limiter

* Add rate limiter with sharded memory store

* Racy access to store.lastCleanup eliminated
Merges in shiny sharded map implementation by @lammel

* Remove RateLimiterShradedMemoryStore for now

* Make fields for RateLimiterStoreConfig public for external configuration

* Improve docs for RateLimiter usage

* Fix ErrorHandler vs. DenyHandler usage for rate limiter

* Simplify NewRateLimiterMemoryStore

* improved coverage

* updated errorHandler and denyHandler to use echo.HTTPError

* Improve wording for error and comments

* Remove duplicate lastSeen marking for Allow

* Improve wording for comments

* Add disclaimer on perf characteristics of memory store

* changes Allow signature on rate limiter to return err too

Co-authored-by: Roland Lammel <rl@neotel.at>
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iambenkay and lammel committed Jan 15, 2021
1 parent 9b0e630 commit 7c8592a
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1 change: 1 addition & 0 deletions .gitignore
Expand Up @@ -5,3 +5,4 @@ vendor
.idea
*.iml
*.out
.vscode
1 change: 1 addition & 0 deletions go.mod
Expand Up @@ -12,4 +12,5 @@ require (
golang.org/x/net v0.0.0-20200822124328-c89045814202
golang.org/x/sys v0.0.0-20200826173525-f9321e4c35a6 // indirect
golang.org/x/text v0.3.3 // indirect
golang.org/x/time v0.0.0-20201208040808-7e3f01d25324
)
2 changes: 2 additions & 0 deletions go.sum
Expand Up @@ -46,6 +46,8 @@ golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
golang.org/x/text v0.3.3 h1:cokOdA+Jmi5PJGXLlLllQSgYigAEfHXJAERHVMaCc2k=
golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
golang.org/x/time v0.0.0-20201208040808-7e3f01d25324 h1:Hir2P/De0WpUhtrKGGjvSb2YxUgyZ7EFOSLIcSSpiwE=
golang.org/x/time v0.0.0-20201208040808-7e3f01d25324/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
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268 changes: 268 additions & 0 deletions middleware/rate_limiter.go
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package middleware

import (
"net/http"
"sync"
"time"

"github.com/labstack/echo/v4"
"golang.org/x/time/rate"
)

type (
// RateLimiterStore is the interface to be implemented by custom stores.
RateLimiterStore interface {
// Stores for the rate limiter have to implement the Allow method
Allow(identifier string) (bool, error)
}
)

type (
// RateLimiterConfig defines the configuration for the rate limiter
RateLimiterConfig struct {
Skipper Skipper
BeforeFunc BeforeFunc
// IdentifierExtractor uses echo.Context to extract the identifier for a visitor
IdentifierExtractor Extractor
// Store defines a store for the rate limiter
Store RateLimiterStore
// ErrorHandler provides a handler to be called when IdentifierExtractor returns an error
ErrorHandler func(context echo.Context, err error) error
// DenyHandler provides a handler to be called when RateLimiter denies access
DenyHandler func(context echo.Context, identifier string, err error) error
}
// Extractor is used to extract data from echo.Context
Extractor func(context echo.Context) (string, error)
)

// errors
var (
// ErrRateLimitExceeded denotes an error raised when rate limit is exceeded
ErrRateLimitExceeded = echo.NewHTTPError(http.StatusTooManyRequests, "rate limit exceeded")
// ErrExtractorError denotes an error raised when extractor function is unsuccessful
ErrExtractorError = echo.NewHTTPError(http.StatusForbidden, "error while extracting identifier")
)

// DefaultRateLimiterConfig defines default values for RateLimiterConfig
var DefaultRateLimiterConfig = RateLimiterConfig{
Skipper: DefaultSkipper,
IdentifierExtractor: func(ctx echo.Context) (string, error) {
id := ctx.RealIP()
return id, nil
},
ErrorHandler: func(context echo.Context, err error) error {
return &echo.HTTPError{
Code: ErrExtractorError.Code,
Message: ErrExtractorError.Message,
Internal: err,
}
},
DenyHandler: func(context echo.Context, identifier string, err error) error {
return &echo.HTTPError{
Code: ErrRateLimitExceeded.Code,
Message: ErrRateLimitExceeded.Message,
Internal: err,
}
},
}

/*
RateLimiter returns a rate limiting middleware
e := echo.New()
limiterStore := middleware.NewRateLimiterMemoryStore(20)
e.GET("/rate-limited", func(c echo.Context) error {
return c.String(http.StatusOK, "test")
}, RateLimiter(limiterStore))
*/
func RateLimiter(store RateLimiterStore) echo.MiddlewareFunc {
config := DefaultRateLimiterConfig
config.Store = store

return RateLimiterWithConfig(config)
}

/*
RateLimiterWithConfig returns a rate limiting middleware
e := echo.New()
config := middleware.RateLimiterConfig{
Skipper: DefaultSkipper,
Store: middleware.NewRateLimiterMemoryStore(
middleware.RateLimiterMemoryStoreConfig{Rate: 10, Burst: 30, ExpiresIn: 3 * time.Minute}
)
IdentifierExtractor: func(ctx echo.Context) (string, error) {
id := ctx.RealIP()
return id, nil
},
ErrorHandler: func(context echo.Context, err error) error {
return context.JSON(http.StatusTooManyRequests, nil)
},
DenyHandler: func(context echo.Context, identifier string) error {
return context.JSON(http.StatusForbidden, nil)
},
}
e.GET("/rate-limited", func(c echo.Context) error {
return c.String(http.StatusOK, "test")
}, middleware.RateLimiterWithConfig(config))
*/
func RateLimiterWithConfig(config RateLimiterConfig) echo.MiddlewareFunc {
if config.Skipper == nil {
config.Skipper = DefaultRateLimiterConfig.Skipper
}
if config.IdentifierExtractor == nil {
config.IdentifierExtractor = DefaultRateLimiterConfig.IdentifierExtractor
}
if config.ErrorHandler == nil {
config.ErrorHandler = DefaultRateLimiterConfig.ErrorHandler
}
if config.DenyHandler == nil {
config.DenyHandler = DefaultRateLimiterConfig.DenyHandler
}
if config.Store == nil {
panic("Store configuration must be provided")
}
return func(next echo.HandlerFunc) echo.HandlerFunc {
return func(c echo.Context) error {
if config.Skipper(c) {
return next(c)
}
if config.BeforeFunc != nil {
config.BeforeFunc(c)
}

identifier, err := config.IdentifierExtractor(c)
if err != nil {
c.Error(config.ErrorHandler(c, err))
return nil
}

if allow, err := config.Store.Allow(identifier); !allow {
c.Error(config.DenyHandler(c, identifier, err))
return nil
}
return next(c)
}
}
}

type (
// RateLimiterMemoryStore is the built-in store implementation for RateLimiter
RateLimiterMemoryStore struct {
visitors map[string]*Visitor
mutex sync.Mutex
rate rate.Limit
burst int
expiresIn time.Duration
lastCleanup time.Time
}
// Visitor signifies a unique user's limiter details
Visitor struct {
*rate.Limiter
lastSeen time.Time
}
)

/*
NewRateLimiterMemoryStore returns an instance of RateLimiterMemoryStore with
the provided rate (as req/s). Burst and ExpiresIn will be set to default values.
Example (with 20 requests/sec):
limiterStore := middleware.NewRateLimiterMemoryStore(20)
*/
func NewRateLimiterMemoryStore(rate rate.Limit) (store *RateLimiterMemoryStore) {
return NewRateLimiterMemoryStoreWithConfig(RateLimiterMemoryStoreConfig{
Rate: rate,
})
}

/*
NewRateLimiterMemoryStoreWithConfig returns an instance of RateLimiterMemoryStore
with the provided configuration. Rate must be provided. Burst will be set to the value of
the configured rate if not provided or set to 0.
The build-in memory store is usually capable for modest loads. For higher loads other
store implementations should be considered.
Characteristics:
* Concurrency above 100 parallel requests may causes measurable lock contention
* A high number of different IP addresses (above 16000) may be impacted by the internally used Go map
* A high number of requests from a single IP address may cause lock contention
Example:
limiterStore := middleware.NewRateLimiterMemoryStoreWithConfig(
middleware.RateLimiterMemoryStoreConfig{Rate: 50, Burst: 200, ExpiresIn: 5 * time.Minutes},
)
*/
func NewRateLimiterMemoryStoreWithConfig(config RateLimiterMemoryStoreConfig) (store *RateLimiterMemoryStore) {
store = &RateLimiterMemoryStore{}

store.rate = config.Rate
store.burst = config.Burst
store.expiresIn = config.ExpiresIn
if config.ExpiresIn == 0 {
store.expiresIn = DefaultRateLimiterMemoryStoreConfig.ExpiresIn
}
if config.Burst == 0 {
store.burst = int(config.Rate)
}
store.visitors = make(map[string]*Visitor)
store.lastCleanup = now()
return
}

// RateLimiterMemoryStoreConfig represents configuration for RateLimiterMemoryStore
type RateLimiterMemoryStoreConfig struct {
Rate rate.Limit // Rate of requests allowed to pass as req/s
Burst int // Burst additionally allows a number of requests to pass when rate limit is reached
ExpiresIn time.Duration // ExpiresIn is the duration after that a rate limiter is cleaned up
}

// DefaultRateLimiterMemoryStoreConfig provides default configuration values for RateLimiterMemoryStore
var DefaultRateLimiterMemoryStoreConfig = RateLimiterMemoryStoreConfig{
ExpiresIn: 3 * time.Minute,
}

// Allow implements RateLimiterStore.Allow
func (store *RateLimiterMemoryStore) Allow(identifier string) (bool, error) {
store.mutex.Lock()
limiter, exists := store.visitors[identifier]
if !exists {
limiter = new(Visitor)
limiter.Limiter = rate.NewLimiter(store.rate, store.burst)
store.visitors[identifier] = limiter
}
limiter.lastSeen = now()
if now().Sub(store.lastCleanup) > store.expiresIn {
store.cleanupStaleVisitors()
}
store.mutex.Unlock()
return limiter.AllowN(now(), 1), nil
}

/*
cleanupStaleVisitors helps manage the size of the visitors map by removing stale records
of users who haven't visited again after the configured expiry time has elapsed
*/
func (store *RateLimiterMemoryStore) cleanupStaleVisitors() {
for id, visitor := range store.visitors {
if now().Sub(visitor.lastSeen) > store.expiresIn {
delete(store.visitors, id)
}
}
store.lastCleanup = now()
}

/*
actual time method which is mocked in test file
*/
var now = func() time.Time {
return time.Now()
}

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