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package routing
import (
"net/http"
"sync"
"time"
"github.com/matrix-org/dendrite/clientapi/jsonerror"
"github.com/matrix-org/dendrite/internal/config"
"github.com/matrix-org/util"
)
type rateLimits struct {
limits map[string]chan struct{}
limitsMutex sync.RWMutex
enabled bool
requestThreshold int64
cooloffDuration time.Duration
}
func newRateLimits(cfg *config.RateLimiting) *rateLimits {
l := &rateLimits{
limits: make(map[string]chan struct{}),
enabled: cfg.Enabled,
requestThreshold: cfg.Threshold,
cooloffDuration: time.Duration(cfg.CooloffMS) * time.Millisecond,
}
if l.enabled {
go l.clean()
}
return l
}
func (l *rateLimits) clean() {
for {
// On a 30 second interval, we'll take an exclusive write
// lock of the entire map and see if any of the channels are
// empty. If they are then we will close and delete them,
// freeing up memory.
time.Sleep(time.Second * 30)
l.limitsMutex.Lock()
for k, c := range l.limits {
if len(c) == 0 {
close(c)
delete(l.limits, k)
}
}
l.limitsMutex.Unlock()
}
}
func (l *rateLimits) rateLimit(req *http.Request) *util.JSONResponse {
// If rate limiting is disabled then do nothing.
if !l.enabled {
return nil
}
// Lock the map long enough to check for rate limiting. We hold it
// for longer here than we really need to but it makes sure that we
// also don't conflict with the cleaner goroutine which might clean
// up a channel after we have retrieved it otherwise.
l.limitsMutex.RLock()
defer l.limitsMutex.RUnlock()
// First of all, work out if X-Forwarded-For was sent to us. If not
// then we'll just use the IP address of the caller.
caller := req.RemoteAddr
if forwardedFor := req.Header.Get("X-Forwarded-For"); forwardedFor != "" {
caller = forwardedFor
}
// Look up the caller's channel, if they have one. If they don't then
// let's create one.
rateLimit, ok := l.limits[caller]
if !ok {
l.limits[caller] = make(chan struct{}, l.requestThreshold)
rateLimit = l.limits[caller]
}
// Check if the user has got free resource slots for this request.
// If they don't then we'll return an error.
select {
case rateLimit <- struct{}{}:
default:
// We hit the rate limit. Tell the client to back off.
return &util.JSONResponse{
Code: http.StatusTooManyRequests,
JSON: jsonerror.LimitExceeded("You are sending too many requests too quickly!", l.cooloffDuration.Milliseconds()),
}
}
// After the time interval, drain a resource from the rate limiting
// channel. This will free up space in the channel for new requests.
go func() {
<-time.After(l.cooloffDuration)
<-rateLimit
}()
return nil
}
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