minio/rate-limit-handler.go

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/*
* Minio Cloud Storage, (C) 2016 Minio, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package main
import (
"errors"
"net/http"
"sync"
)
var errTooManyRequests = errors.New("Too many clients in the waiting list")
// rateLimit - represents datatype of the functionality implemented to
// limit the number of concurrent http requests.
type rateLimit struct {
handler http.Handler
lock sync.Mutex
workQueue chan struct{}
waitQueue chan struct{}
}
// acquire and release implement a way to send and receive from the
// channel this is in-turn used to rate limit incoming connections in
// ServeHTTP() http.Handler method.
func (c *rateLimit) acquire() error {
// Kick out clients when it is really crowded
if len(c.waitQueue) == cap(c.waitQueue) {
return errTooManyRequests
}
// Add new element in waitQueue to keep track of clients
// wanting to process their requests
c.waitQueue <- struct{}{}
// Moving from wait to work queue is protected by a mutex
// to avoid draining waitQueue with multiple simultaneous clients.
c.lock.Lock()
c.workQueue <- <-c.waitQueue
c.lock.Unlock()
return nil
}
// Release one element from workQueue to serve a new client
// in the waiting list
func (c *rateLimit) release() {
<-c.workQueue
}
// ServeHTTP is an http.Handler ServeHTTP method, implemented to rate
// limit incoming HTTP requests.
func (c *rateLimit) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// Acquire the connection if queue is not full, otherwise
// code path waits here until the previous case is true.
if err := c.acquire(); err != nil {
w.WriteHeader(http.StatusTooManyRequests)
return
}
// Serves the request.
c.handler.ServeHTTP(w, r)
// Release
c.release()
}
// setRateLimitHandler limits the number of concurrent http requests based on MINIO_MAXCONN.
func setRateLimitHandler(handler http.Handler) http.Handler {
if globalMaxConn == 0 {
return handler
} // else proceed to rate limiting.
// For max connection limit of > '0' we initialize rate limit handler.
return &rateLimit{
handler: handler,
workQueue: make(chan struct{}, globalMaxConn),
waitQueue: make(chan struct{}, globalMaxConn*4),
}
}