我在ubuntu linux 16.04上运行了这个UDP客户端程序:
package main
import (
"fmt"
"net"
"time"
"strconv"
)
func CheckError(err error) {
if err != nil {
fmt.Println("Error: " , err)
}
}
func main() {
ServerAddr,err := net.ResolveUDPAddr("udp","127.0.0.1:10001")
CheckError(err)
LocalAddr, err := net.ResolveUDPAddr("udp", "127.0.0.1:0")
CheckError(err)
Conn, err := net.DialUDP("udp", LocalAddr, ServerAddr)
CheckError(err)
defer Conn.Close()
i := 0
for {
msg := strconv.Itoa(i)
i++
buf := []byte(msg)
_,err := Conn.Write(buf)
if err != nil {
fmt.Println(msg, err)
}
time.Sleep(time.Second * 1)
}
}
它产生这个输出:
$ go run server.go
1 write udp 127.0.0.1:58703->127.0.0.1:10001: write: connection refused
3 write udp 127.0.0.1:58703->127.0.0.1:10001: write: connection refused
5 write udp 127.0.0.1:58703->127.0.0.1:10001: write: connection refused
但我期待这个输出:
$ go run server.go
1 write udp 127.0.0.1:58703->127.0.0.1:10001: write: connection refused
2 write udp 127.0.0.1:58703->127.0.0.1:10001: write: connection refused
3 write udp 127.0.0.1:58703->127.0.0.1:10001: write: connection refused
4 write udp 127.0.0.1:58703->127.0.0.1:10001: write: connection refused
5 write udp 127.0.0.1:58703->127.0.0.1:10001: write: connection refused
tcpdump说:
15:28:46.453313 IP localhost.47993 > localhost.10001: UDP, length 1
15:28:46.453338 IP localhost > localhost: ICMP localhost udp port 10001 unreachable, length 37
15:28:48.453821 IP localhost.47993 > localhost.10001: UDP, length 1
15:28:48.453852 IP localhost > localhost: ICMP localhost udp port 10001 unreachable, length 37
15:28:50.454242 IP localhost.47993 > localhost.10001: UDP, length 1
15:28:50.454271 IP localhost > localhost: ICMP localhost udp port 10001 unreachable, length 37
为什么每隔一段时间就会发生这种情况conn.Write写入而不是每次都写?我不会责怪去,我只是想了解原因。
答案 0 :(得分:5)
如果你仔细查看数据包捕获,你会注意到 回复每个ICMP无法访问的数据包,你只是发送每隔一个包。如果从Write
检查返回值,您还会看到没有其他数据包写入数据。
因为UDP没有真正的连接,并且对于发送的任何数据包都没有ACK,所以最好的"连接" UDP套接字可以模拟发送失败是为了保存ICMP响应,并在下次写入时将其作为错误返回。
因此发送第一个数据包,收到ICMP不可达消息,第二个发送操作失败并返回错误,因此不发送数据包,循环重复。
答案 1 :(得分:0)
尝试
LocalAddr, err := net.ResolveUDPAddr("udp", ":0")
或
LocalAddr, err := net.ResolveUDPAddr("udp", "<ip address of outgoing interface>:0")
这应该有效