donglang6656 2016-04-01 18:25
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运行带有超时的命令并一次进入stdout一行

I'd like to run a command and print each line from its stdout (as it becomes available). Further, if the command doesn't complete within N seconds, I would like to terminate it as well.

There are some examples of implementing timeouts in golang (notably Terminating a Process Started with os/exec in Golang). I have a time.After() clause in select that I expect to hit after 2 seconds, at which point RunTraceroute should return - but this doesn't happen.

My code is below (and on go playground: http://play.golang.org/p/D4AcoaweMt)

package main

import (
    "bufio"
    "fmt"
    "log"
    "os"
    "os/exec"
    "time"
)

func RunTraceroute(host string) {
    errch := make(chan error, 1)
    cmd := exec.Command("/usr/bin/traceroute", host)
    stdout, err := cmd.StdoutPipe()
    if err != nil {
        log.Fatal(err)
    }
    if err := cmd.Start(); err != nil {
        log.Fatal(err)
    }
    go func() {
        errch <- cmd.Wait()
    }()
    select {
    case <-time.After(time.Second * 2):
        log.Println("Timeout hit..")
        return
    case err := <-errch:
        if err != nil {
            log.Println("traceroute failed:", err)
        }
    default:
        for _, char := range "|/-\\" {
            fmt.Printf("%s...%c", "Running traceroute", char)
            time.Sleep(100 * time.Millisecond)
        }
        scanner := bufio.NewScanner(stdout)
        fmt.Println("")
        for scanner.Scan() {
            line := scanner.Text()
            log.Println(line)
        }
    }
}

func main() {
    RunTraceroute(os.Args[1])
}

Output (snipped out first few lines of local ip addresses and gateway):

$ go run pipe.go xinhua.com
Running traceroute...\
2016/04/01 11:16:43 traceroute to xinhua.com (58.64.200.76), 30 hops max, 60 byte packets
.......
.......
.....More deleted lines.....

2016/04/01 11:16:49 12  * * *
2016/04/01 11:16:49 13  4.68.63.214 (4.68.63.214)  3.208 ms  3.176 ms  3.241 ms
2016/04/01 11:16:49 14  * * *
2016/04/01 11:16:49 15  if-ae-9-2.tcore1.TV2-Tokyo.as6453.net (180.87.180.18)  160.314 ms  158.837 ms  161.438 ms
2016/04/01 11:16:49 16  if-ae-5-7.tcore1.HK2-Hong-Kong.as6453.net (180.87.112.189)  157.497 ms if-ae-3-2.tcore1.HK2-Hong-Kong.as6453.net (180.87.112.5)  161.397 ms if-ae-5-7.tcore1.HK2-Hong-Kong.as6453.net (180.87.112.189)  159.351 ms
2016/04/01 11:16:49 17  if-ge-10-0-0-1128.core1.undefined.as6453.net (180.87.160.73)  156.412 ms  156.522 ms if-ge-14-0-0-1126.core1.undefined.as6453.net (180.87.112.30)  156.605 ms
2016/04/01 11:16:49 18  * * *
2016/04/01 11:16:49 19  * * *
2016/04/01 11:16:49 20  * * *
2016/04/01 11:16:49 21  113.10.229.113 (113.10.229.113)  165.578 ms  165.818 ms  163.451 ms
2016/04/01 11:16:49 22  113.10.229.74 (113.10.229.74)  163.564 ms ae5.10g-idc.wpc.nwtgigalink.com (113.10.229.66)  162.384 ms 113.10.229.74 (113.10.229.74)  167.026 ms
2016/04/01 11:16:49 23  113.10.230.162 (113.10.230.162)  162.988 ms  162.777 ms  163.807 ms
2016/04/01 11:16:49 24  58.64.160.164 (58.64.160.164)  161.902 ms  162.396 ms  164.986 ms
2016/04/01 11:16:54 25  * * *
2016/04/01 11:16:54 26  58.64.200.76 (58.64.200.76)  162.178 ms !X  162.509 ms !X  162.356 ms !X
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