101 lines
2.8 KiB
Go
101 lines
2.8 KiB
Go
/*
|
|
* 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 cmd
|
|
|
|
import (
|
|
"errors"
|
|
"net/http"
|
|
)
|
|
|
|
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
|
|
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 {
|
|
// attempt to enter the waitQueue. If no slot is immediately
|
|
// available return error.
|
|
select {
|
|
case c.waitQueue <- struct{}{}:
|
|
// entered wait queue
|
|
break
|
|
default:
|
|
// no slot available for waiting
|
|
return errTooManyRequests
|
|
}
|
|
|
|
// block attempting to enter the workQueue. If the workQueue
|
|
// is full, there can be at most cap(waitQueue) ==
|
|
// 4*globalMaxConn goroutines waiting here because of the
|
|
// select above.
|
|
select {
|
|
case c.workQueue <- struct{}{}:
|
|
// entered workQueue - so remove one waiter. This step
|
|
// does not block as the waitQueue cannot be empty.
|
|
<-c.waitQueue
|
|
}
|
|
|
|
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),
|
|
}
|
|
}
|