1.前言
因为公司业务需要在自己的私有云服务器上添加添加WebSsh终端,同时提供输入命令审计功能.
从google上可以了解到xterm.js是一个非常出色的web终端库,包括VSCode很多成熟的产品都使用这个前端库.使用起来也比较简单.
难点是怎么把ssh命令行转换成websocket通讯,来提供Stdin,stdout输出到xterm.js中,接下来就详解技术细节.
全部代码都可以在我的Github.com/dejavuzhou/felix中可以查阅到.
2.知识储备
linux下载stdin,stdou和stderr简单概念
熟悉Golang官方库golang.org/x/crypto/ssh
了解gorilla/websocket的基本用法
gin-gonic/gin,当然你也可以使用其他的路由包替代,或者直接使用标准库
(前端)websocket
(前端)xterm.js
3.数据逻辑图
Golang堡垒机主要功能就是把SSH协议数据使用websocket协议转发给xterm.js浏览器.
堡垒机Golang服务UML
4.代码实现
4.1创建gin Handler func
注册gin路由 api.GET("ws/:id", internal.WsSsh)
ssh2ws/internal/ws_ssh.go
package internal
import (
"bytes"
"github.com/dejavuzhou/felix/flx"
"github.com/dejavuzhou/felix/models"
"github.com/dejavuzhou/felix/utils"
"github.com/gin-gonic/gin"
"github.com/gorilla/websocket"
"github.com/sirupsen/logrus"
"net/http"
"strconv"
"time"
)
var upGrader = websocket.Upgrader{
ReadBufferSize: 1024,
WriteBufferSize: 1024 * 1024 * 10,
CheckOrigin: func(r *http.Request) bool {
return true
},
}
// handle webSocket connection.
// first,we establish a ssh connection to ssh server when a webSocket comes;
// then we deliver ssh data via ssh connection between browser and ssh server.
// That is, read webSocket data from browser (e.g. 'ls' command) and send data to ssh server via ssh connection;
// the other hand, read returned ssh data from ssh server and write back to browser via webSocket API.
func WsSsh(c *gin.Context) {
v, ok := c.Get("user")
if !ok {
logrus.Error("jwt token can't find auth user")
return
}
userM, ok := v.(*models.User)
if !ok {
logrus.Error("context user is not a models.User type obj")
return
}
cols, err := strconv.Atoi(c.DefaultQuery("cols", "120"))
if wshandleError(c, err) {
return
}
rows, err := strconv.Atoi(c.DefaultQuery("rows", "32"))
if wshandleError(c, err) {
return
}
idx, err := parseParamID(c)
if wshandleError(c, err) {
return
}
mc, err := models.MachineFind(idx)
if wshandleError(c, err) {
return
}
client, err := flx.NewSshClient(mc)
if wshandleError(c, err) {
return
}
defer client.Close()
startTime := time.Now()
ssConn, err := utils.NewSshConn(cols, rows, client)
if wshandleError(c, err) {
return
}
defer ssConn.Close()
// after configure, the WebSocket is ok.
wsConn, err := upGrader.Upgrade(c.Writer, c.Request, nil)
if wshandleError(c, err) {
return
}
defer wsConn.Close()
quitChan := make(chan bool, 3)
var logBuff = new(bytes.Buffer)
// most messages are ssh output, not webSocket input
go ssConn.ReceiveWsMsg(wsConn, logBuff, quitChan)
go ssConn.SendComboOutput(wsConn, quitChan)
go ssConn.SessionWait(quitChan)
<-quitChan
//write logs
xtermLog := models.TermLog{
EndTime: time.Now(),
StartTime: startTime,
UserId: userM.ID,
Log: logBuff.String(),
MachineId: idx,
MachineName: mc.Name,
MachineIp: mc.Ip,
MachineHost: mc.Host,
UserName: userM.Username,
}
err = xtermLog.Create()
if wshandleError(c, err) {
return
}
logrus.Info("websocket finished")
}
代码详解
31~52行使用gin来获取url中的参数(js websocket库)只可以把参数定义到cookie和和url-query中,所以这里包括token(不是在header-Authorization中)在内的参数全部在url中获取
53~56行到数据库中获取保存的ssh连接信息
57~68行创建ssh-session
69~74行升级得到websocketConn(Reader/Writer)
75~85行(核心代码)ssh Session 和 websocket 信息进行交换和处理,同时处理好线程退出
86~104行处理ssh输入命令(logBuff),当session结束的时候技术输入的命令到数据库中,提供日后审计只用
4.1.1 func NewSshConn(cols, rows int, sshClient *ssh.Client) (*SshConn, error)创建ssh-session-pty
I 获取stdin pipline stdinP, err := sshSession.StdinPipe()
II 初始化wsBufferWriter,赋值给ssh-session.Stdout和ssh-session.Stderr
type wsBufferWriter struct {
buffer bytes.Buffer
mu sync.Mutex
}
...
...
...
comboWriter := new(wsBufferWriter)
//ssh.stdout and stderr will write output into comboWriter
sshSession.Stdout = comboWriter
sshSession.Stderr = comboWriter
现在comboWriter就是sshSession的stdout和stderr,可以通过comboWriter获取ssh输出
4.2 第75~85行核心代码解析
4.2.1 quitChan 用来处理 for select loop退出,代码示例
for {
select {
case <-quitChan:
//exit loop
return
default:
fmt.Println("do some stuff")
}
}
4.2.2 var logBuff = new(bytes.Buffer) 暂存session中的stdin命令,websocket session 结束之后,获取logBuff.String(),写入数据库
Log: logBuff.String(),
...
<-quitChan
//write logs
xtermLog := models.TermLog{
EndTime: time.Now(),
StartTime: startTime,
UserId: userM.ID,
Log: logBuff.String(),
MachineId: idx,
MachineName: mc.Name,
MachineIp: mc.Ip,
MachineHost: mc.Host,
UserName: userM.Username,
}
err = xtermLog.Create()
if wshandleError(c, err) {
return
}
...
4.2.3 go ssConn.ReceiveWsMsg(wsConn, logBuff, quitChan)
处理ws消息并转发给ssh-Session stdinPipe,同时暂存消息到logBuff
//ReceiveWsMsg receive websocket msg do some handling then write into ssh.session.stdin
func (ssConn *SshConn) ReceiveWsMsg(wsConn *websocket.Conn, logBuff *bytes.Buffer, exitCh chan bool) {
//tells other go routine quit
defer setQuit(exitCh)
for {
select {
case <-exitCh:
return
default:
//read websocket msg
_, wsData, err := wsConn.ReadMessage()
if err != nil {
logrus.WithError(err).Error("reading webSocket message failed")
return
}
//unmashal bytes into struct
msgObj := wsMsg{}
if err := json.Unmarshal(wsData, &msgObj); err != nil {
logrus.WithError(err).WithField("wsData", string(wsData)).Error("unmarshal websocket message failed")
}
switch msgObj.Type {
case wsMsgResize:
//handle xterm.js size change
if msgObj.Cols > 0 && msgObj.Rows > 0 {
if err := ssConn.Session.WindowChange(msgObj.Rows, msgObj.Cols); err != nil {
logrus.WithError(err).Error("ssh pty change windows size failed")
}
}
case wsMsgCmd:
//handle xterm.js stdin
decodeBytes, err := base64.StdEncoding.DecodeString(msgObj.Cmd)
if err != nil {
logrus.WithError(err).Error("websock cmd string base64 decoding failed")
}
if _, err := ssConn.StdinPipe.Write(decodeBytes); err != nil {
logrus.WithError(err).Error("ws cmd bytes write to ssh.stdin pipe failed")
}
//write input cmd to log buffer
if _, err := logBuff.Write(decodeBytes); err != nil {
logrus.WithError(err).Error("write received cmd into log buffer failed")
}
}
}
}
}
_, wsData, err := wsConn.ReadMessage() 读取websocket 发送的消息
if err := json.Unmarshal(wsData, &msgObj); err != nil { 序列化消息,消息结构必须前端xterm.js-websocket协商一直,建议使用
const (
wsMsgCmd = "cmd"//处理ssh命令
wsMsgResize = "resize"//处理xterm.js dom尺寸变化事件,详解xterm.js文档
)
type wsMsg struct {
Type string `json:"type"`
Cmd string `json:"cmd"`
Cols int `json:"cols"`
Rows int `json:"rows"`
}
-
case wsMsgResize处理xterm.js 终端尺寸变化事件
wsMsgCmd 处理xterm.js 命令输入
if _, err := ssConn.StdinPipe.Write(decodeBytes); err != nil { 把ws xterm.js,前端input命令写入到ssh-session-stdin-pipline
ssh.seesion 如果检测到到 decodeBytes 包含执行符('r'),sshSession会执行命令,包把执行结果输出到comboWriter
if _, err := logBuff.Write(decodeBytes); err != nil { 把ws.xterm.js 前端input命令记录到 logBuff
4.2.4 go ssConn.SendComboOutput(wsConn, quitChan)
把ssh.Session的comboWriter中的数据每隔120ms 通过调用websocketConn.WriteMessage方法返回给xterm.js+websocketClient 前端
func (ssConn *SshConn) SendComboOutput(wsConn *websocket.Conn, exitCh chan bool) {
//tells other go routine quit
defer setQuit(exitCh)
//every 120ms write combine output bytes into websocket response
tick := time.NewTicker(time.Millisecond * time.Duration(120))
//for range time.Tick(120 * time.Millisecond){}
defer tick.Stop()
for {
select {
case <-tick.C:
//write combine output bytes into websocket response
if err := flushComboOutput(ssConn.ComboOutput, wsConn); err != nil {
logrus.WithError(err).Error("ssh sending combo output to webSocket failed")
return
}
case <-exitCh:
return
}
}
}
...
...
...
//flushComboOutput flush ssh.session combine output into websocket response
func flushComboOutput(w *wsBufferWriter, wsConn *websocket.Conn) error {
if w.buffer.Len() != 0 {
err := wsConn.WriteMessage(websocket.TextMessage, w.buffer.Bytes())
if err != nil {
return err
}
w.buffer.Reset()
}
return nil
}
4.2.5 go ssConn.SessionWait(quitChan)
注意这里的go 关键字不能去掉,否在导致不能处理quitChan,导致协程泄露.
func (ssConn *SshConn) SessionWait(quitChan chan bool) {
if err := ssConn.Session.Wait(); err != nil {
logrus.WithError(err).Error("ssh session wait failed")
setQuit(quitChan)
}
}
4.前端vuejs.demo代码
可以提供给前端开发人员参考,当然可以让他直接查xterm.js官方文档,但是websocket 数据库结构必须前后端协商一致
vuejs+xterm.js+websocket示例代码
<template>
<el-dialog :visible.sync="v"
:title="obj.user + '@' + obj.host"
@opened="doOpened"
@open="doOpen"
@close="doClose"
center
fullscreen
>
<div ref="terminal"></div>
</el-dialog>
</template>
<script>
import {Terminal} from "xterm";
import * as fit from "xterm/lib/addons/fit/fit";
import {Base64} from "js-base64";
import * as webLinks from "xterm/lib/addons/webLinks/webLinks";
import * as search from "xterm/lib/addons/search/search";
import "xterm/lib/addons/fullscreen/fullscreen.css";
import "xterm/dist/xterm.css"
import config from "@/config/config"
let defaultTheme = {
foreground: "#ffffff",
background: "#1b212f",
cursor: "#ffffff",
selection: "rgba(255, 255, 255, 0.3)",
black: "#000000",
brightBlack: "#808080",
red: "#ce2f2b",
brightRed: "#f44a47",
green: "#00b976",
brightGreen: "#05d289",
yellow: "#e0d500",
brightYellow: "#f4f628",
magenta: "#bd37bc",
brightMagenta: "#d86cd8",
blue: "#1d6fca",
brightBlue: "#358bed",
cyan: "#00a8cf",
brightCyan: "#19b8dd",
white: "#e5e5e5",
brightWhite: "#ffffff"
};
let bindTerminalResize = (term, websocket) => {
let onTermResize = size => {
websocket.send(
JSON.stringify({
type: "resize",
rows: size.rows,
cols: size.cols
})
);
};
// register resize event.
term.on("resize", onTermResize);
// unregister resize event when WebSocket closed.
websocket.addEventListener("close", function () {
term.off("resize", onTermResize);
});
};
let bindTerminal = (term, websocket, bidirectional, bufferedTime) => {
term.socket = websocket;
let messageBuffer = null;
let handleWebSocketMessage = function (ev) {
if (bufferedTime && bufferedTime > 0) {
if (messageBuffer) {
messageBuffer += ev.data;
} else {
messageBuffer = ev.data;
setTimeout(function () {
term.write(messageBuffer);
}, bufferedTime);
}
} else {
term.write(ev.data);
}
};
let handleTerminalData = function (data) {
websocket.send(
JSON.stringify({
type: "cmd",
cmd: Base64.encode(data) // encode data as base64 format
})
);
};
websocket.onmessage = handleWebSocketMessage;
if (bidirectional) {
term.on("data", handleTerminalData);
}
// send heartbeat package to avoid closing webSocket connection in some proxy environmental such as nginx.
let heartBeatTimer = setInterval(function () {
websocket.send(JSON.stringify({type: "heartbeat", data: ""}));
}, 20 * 1000);
websocket.addEventListener("close", function () {
websocket.removeEventListener("message", handleWebSocketMessage);
term.off("data", handleTerminalData);
delete term.socket;
clearInterval(heartBeatTimer);
});
};
export default {
props: {obj: {type: Object, require: true}, visible: Boolean},
name: "CompTerm",
data() {
return {
isFullScreen:false,
searchKey:"",
v: this.visible,
ws: null,
term: null,
thisV: this.visible
};
},
watch: {
visible(val) {
this.v = val;//新增result的watch，监听变更并同步到myResult上
}
},
computed: {
wsUrl() {
let token = localStorage.getItem('token');
return `${config.wsBase}/api/ws/${this.obj.ID || 0}?cols=${this.term.cols}&rows=${this.term.rows}&_t=${token}`
}
},
methods: {
onWindowResize() {
//console.log("resize")
this.term.fit(); // it will make terminal resized.
},
doLink(ev, url) {
if (ev.type === 'click') {
window.open(url)
}
},
doClose() {
window.removeEventListener("resize", this.onWindowResize);
// term.off("resize", this.onTerminalResize);
if (this.ws) {
this.ws.close()
}
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