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// Copyright (c) 2017 Uber Technologies, 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 utils
import (
"errors"
"net"
)
// This code is borrowed from https://github.com/uber/tchannel-go/blob/dev/localip.go
// scoreAddr scores how likely the given addr is to be a remote address and returns the
// IP to use when listening. Any address which receives a negative score should not be used.
// Scores are calculated as:
// -1 for any unknown IP addresses.
// +300 for IPv4 addresses
// +100 for non-local addresses, extra +100 for "up" interaces.
func scoreAddr(iface net.Interface, addr net.Addr) (int, net.IP) {
var ip net.IP
if netAddr, ok := addr.(*net.IPNet); ok {
ip = netAddr.IP
} else if netIP, ok := addr.(*net.IPAddr); ok {
ip = netIP.IP
} else {
return -1, nil
}
var score int
if ip.To4() != nil {
score += 300
}
if iface.Flags&net.FlagLoopback == 0 && !ip.IsLoopback() {
score += 100
if iface.Flags&net.FlagUp != 0 {
score += 100
}
}
return score, ip
}
// HostIP tries to find an IP that can be used by other machines to reach this machine.
func HostIP() (net.IP, error) {
interfaces, err := net.Interfaces()
if err != nil {
return nil, err
}
bestScore := -1
var bestIP net.IP
// Select the highest scoring IP as the best IP.
for _, iface := range interfaces {
addrs, err := iface.Addrs()
if err != nil {
// Skip this interface if there is an error.
continue
}
for _, addr := range addrs {
score, ip := scoreAddr(iface, addr)
if score > bestScore {
bestScore = score
bestIP = ip
}
}
}
if bestScore == -1 {
return nil, errors.New("no addresses to listen on")
}
return bestIP, nil
}
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