mirror of
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101 lines
2.8 KiB
Go
101 lines
2.8 KiB
Go
/*
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* Minio Cloud Storage, (C) 2016 Minio, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package cmd
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import (
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"errors"
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"net/http"
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)
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var errTooManyRequests = errors.New("Too many clients in the waiting list")
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// rateLimit - represents datatype of the functionality implemented to
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// limit the number of concurrent http requests.
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type rateLimit struct {
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handler http.Handler
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workQueue chan struct{}
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waitQueue chan struct{}
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}
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// acquire and release implement a way to send and receive from the
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// channel this is in-turn used to rate limit incoming connections in
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// ServeHTTP() http.Handler method.
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func (c *rateLimit) acquire() error {
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// attempt to enter the waitQueue. If no slot is immediately
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// available return error.
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select {
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case c.waitQueue <- struct{}{}:
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// entered wait queue
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break
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default:
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// no slot available for waiting
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return errTooManyRequests
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}
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// block attempting to enter the workQueue. If the workQueue
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// is full, there can be at most cap(waitQueue) ==
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// 4*globalMaxConn goroutines waiting here because of the
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// select above.
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select {
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case c.workQueue <- struct{}{}:
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// entered workQueue - so remove one waiter. This step
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// does not block as the waitQueue cannot be empty.
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<-c.waitQueue
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}
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return nil
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}
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// Release one element from workQueue to serve a new client in the
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// waiting list
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func (c *rateLimit) release() {
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<-c.workQueue
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}
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// ServeHTTP is an http.Handler ServeHTTP method, implemented to rate
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// limit incoming HTTP requests.
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func (c *rateLimit) ServeHTTP(w http.ResponseWriter, r *http.Request) {
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// Acquire the connection if queue is not full, otherwise
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// code path waits here until the previous case is true.
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if err := c.acquire(); err != nil {
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w.WriteHeader(http.StatusTooManyRequests)
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return
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}
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// Serves the request.
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c.handler.ServeHTTP(w, r)
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// Release
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c.release()
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}
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// setRateLimitHandler limits the number of concurrent http requests
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// based on MINIO_MAXCONN.
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func setRateLimitHandler(handler http.Handler) http.Handler {
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if globalMaxConn == 0 {
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return handler
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} // else proceed to rate limiting.
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// For max connection limit of > '0' we initialize rate limit
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// handler.
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return &rateLimit{
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handler: handler,
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workQueue: make(chan struct{}, globalMaxConn),
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waitQueue: make(chan struct{}, globalMaxConn*4),
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}
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}
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