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freeport.go
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// Copyright 2020 PingCAP, 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,
// See the License for the specific language governing permissions and
// limitations under the License.
package utils
import (
"fmt"
"net"
"sync"
"time"
)
// To avoid the same port be generated twice in a short time
var portCache sync.Map
// GetFreePort asks the kernel for a free open port that is ready to use.
func GetFreePort(host string, priority int) (int, error) {
if port, err := getPort(host, priority); err == nil {
return port, nil
} else if port, err := getPort(host, 0); err == nil {
return port, nil
} else {
return 0, err
}
}
// MustGetFreePort asks the kernel for a free open port that is ready to use, if fail, panic
func MustGetFreePort(host string, priority int) int {
if port, err := GetFreePort(host, priority); err == nil {
return port
}
panic("can't get a free port")
}
func getPort(host string, port int) (int, error) {
addr, err := net.ResolveTCPAddr("tcp", fmt.Sprintf("%s:%d", host, port))
if err != nil {
return 0, err
}
l, err := net.ListenTCP("tcp", addr)
if err != nil {
return 0, err
}
port = l.Addr().(*net.TCPAddr).Port
l.Close()
key := fmt.Sprintf("%s:%d", host, port)
if t, ok := portCache.Load(key); ok && t.(time.Time).Add(time.Minute).After(time.Now()) {
return getPort(host, (port+1)%65536)
}
portCache.Store(key, time.Now())
return port, nil
}