github.com/bazelbuild/rules_webtesting@v0.2.0/go/portpicker/port_picker.go (about)

     1  // Copyright 2016 Google Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //      http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // Package portpicker provides methods for picking unused TCP ports.
    16  package portpicker
    17  
    18  import (
    19  	"errors"
    20  	"io"
    21  	"net"
    22  	"strconv"
    23  )
    24  
    25  var claimedPorts = map[int]bool{}
    26  
    27  // PickUnusedPort picks an unused TCP port.
    28  func PickUnusedPort() (int, error) {
    29  	var listeners []io.Closer
    30  	defer func() {
    31  		for _, c := range listeners {
    32  			c.Close()
    33  		}
    34  	}()
    35  
    36  	for i := 0; i <= len(claimedPorts); i++ {
    37  		l, err := net.Listen("tcp", ":0")
    38  		if err != nil {
    39  			return 0, err
    40  		}
    41  		listeners = append(listeners, l)
    42  
    43  		_, p, err := net.SplitHostPort(l.Addr().String())
    44  		if err != nil {
    45  			return 0, err
    46  		}
    47  
    48  		port, err := strconv.Atoi(p)
    49  		if err != nil {
    50  			return 0, err
    51  		}
    52  
    53  		if !claimedPorts[port] {
    54  			claimedPorts[port] = true
    55  			return port, nil
    56  		}
    57  	}
    58  	return 0, errors.New("unable to get a port")
    59  }