记一次websocket车祸

写在前面

最近在修改调试系统中的日志展示，日志展示用的是websocket，用curl不好测试，所以动手写了一个客户端来查看系统日志。

websocket client

代码如下（代码中有bug，不要复制粘贴）

package main

import (
    "fmt"
    "log"
    "os"
    "os/signal"
    "syscall"

    "golang.org/x/net/websocket"
)

func main() {
    url := os.Args[1]
    origin := os.Args[2]
    fmt.Printf("Dial url: %s ,origin: %s\n", url, origin)
    ws, err := websocket.Dial(url, "", origin)
    if err != nil {
        log.Fatal(err)
    }

    var msg = make([]byte, 512)
    go func() {
        for {
            ws.Read(msg)
            m, err := ws.Read(msg)
            if err != nil {
                log.Fatal(err)
            }
            fmt.Printf("%s\n", msg[:m])
        }
    }()

    errs := make(chan error, 2)
    go func() {
        c := make(chan os.Signal)
        signal.Notify(c, syscall.SIGINT)
        errs <- fmt.Errorf("%s", <-c)
    }()
    fmt.Printf("terminated: %v", <-errs)
    ws.Close() //关闭连接
}

然后编译执行，发现只打印了偶数行？

 ./wscat ws://127.0.0.1:8888/watch/clusterlog?clusterid=cb63a0bc-8273-45ef-a966-67b46968e518  http://127.0.0.1:8888
Dial url: ws://127.0.0.1:8888/watch/clusterlog?clusterid=cb63a0bc-8273-45ef-a966-67b46968e518 ,origin: http://127.0.0.1:8888
Receive: b
Receive: d
Receive: f
Receive: h

没多想，由于server端代码不太熟，先入为主的以为是server端的问题（因为client端代码太少了，太盲目自大了），所以拆分核心处理模块，把server精简成一个小程序来测试，这里贴上server端代码：

package main

import (
    "fmt"
    "net/http"
    "strings"
    "time"

    "github.com/hpcloud/tail"
    "golang.org/x/net/websocket"
)

func echoHandler(ws *websocket.Conn) {
    cid := ws.Request().URL.Query().Get("clusterid")

    // get agent ansible output log.
    filename := "/var/log/" + cid + ".idx"
    t, err := tail.TailFile(filename, tail.Config{
        ReOpen: true,
        Follow: true,
        // Location:  &tail.SeekInfo{Offset: 0, Whence: 2},
        MustExist: false,
        Poll:      true,
    })
    if err != nil {
        fmt.Println("tail file err:", err)
        return
    }
    var line *tail.Line
    var ok bool
    lastwoline := false
    for {
        line, ok = <-t.Lines
        if !ok {
            time.Sleep(100 * time.Millisecond)
            continue
        }
        _, err := ws.Write([]byte(line.Text))
        if err != nil {
            fmt.Printf("Error: %s", err)
            return
        }
        if lastwoline {
            break
        }
        if strings.Contains(line.Text, "PLAY RECAP") {
            lastwoline = true
        }
    }
}

func main() {
    http.Handle("/watch/clusterlog", websocket.Handler(echoHandler))

    err := http.ListenAndServe(":8080", nil)

    if err != nil {
        panic("ListenAndServe: " + err.Error())
    }
}

还是没什么卵用，还是只打印log的奇数行，看代码不仔细，下面祭出golang的单步代码调试神器：delve，详情见下节golang单步调试神器delve。
错误原因是wscat的32行，ws.Read读了两遍

以上↑