3. 建立Appium Server和Bootstrap的连接

Appium.prototype.invoke = function (cb) {
  this.sessionId = UUID.create().hex;
  logger.debug('Creating new appium session ' + this.sessionId);

  if (this.device.args.autoLaunch === false) {
    ...
     } else {
    // the normal case, where we launch the device for folks

    var onStart = function (err, sessionIdOverride) {
      if (sessionIdOverride) {
        this.sessionId = sessionIdOverride;
        logger.debug("Overriding session id with " +
                    JSON.stringify(sessionIdOverride));
      }
      if (err) return this.cleanupSession(err, cb);
      logger.debug("Device launched! Ready for commands");
      this.setCommandTimeout(this.desiredCapabilities.newCommandTimeout);
      cb(null, this.device);
    }.bind(this);

    this.device.start(onStart, _.once(this.cleanupSession.bind(this)));
  }
};

Android.prototype.start = function (cb, onDie) {
  this.launchCb = cb;
  this.uiautomatorExitCb = onDie;
  logger.info("Starting android appium");

  if (this.adb === null) {
    this.adb = new ADB(this.args);
  }

  if (this.uiautomator === null) {
    this.uiautomator = new UiAutomator(this.adb, this.args);
    this.uiautomator.setExitHandler(this.onUiautomatorExit.bind(this));
  }

  logger.debug("Using fast reset? " + this.args.fastReset);
  async.series([
    this.prepareDevice.bind(this),
    this.packageAndLaunchActivityFromManifest.bind(this),
    this.checkApiLevel.bind(this),
    this.pushStrings.bind(this),
    this.processFromManifest.bind(this),
    this.uninstallApp.bind(this),
    this.installAppForTest.bind(this),
    this.forwardPort.bind(this),
    this.pushAppium.bind(this),
    this.initUnicode.bind(this),
    this.pushSettingsApp.bind(this),
    this.pushUnlock.bind(this),
    this.uiautomator.start.bind(this.uiautomator),
    this.wakeUp.bind(this),
    this.unlock.bind(this),
    this.getDataDir.bind(this),
    this.setupCompressedLayoutHierarchy.bind(this),
    this.startAppUnderTest.bind(this),
    this.initAutoWebview.bind(this)
  ], function (err) {
    if (err) {
      this.shutdown(function () {
        this.launchCb(err);
      }.bind(this));
    } else {
      this.didLaunch = true;
      this.launchCb(null, this.proxySessionId);
    }
  }.bind(this));
};

• 建立adb，代码跟踪进去可以见到建立adb不是在appium server本身的源码里面实现的，调用的是另外一个叫"appium-adb"的库，我手头没有源码，所以就不去看它了，但是不用看我都猜到是怎么回事，无非就是像本人以前分析《MonkeyRunner源码分析之启动》时分析chimpchat一样，把adb给封装一下，然后提供一些额外的方便使用的方法出来而已
• 创建uiautomator这个底层与bootstrap和目标机器交互的类的实例，既然需要和目标机器交互，那么刚才的adb时必须作为参数传进去的了。大家还记得上面提到的在初始化Android这个设备类的时候uiautomator这个变量时设置成null的吧，其实它是在这个时候进行实例化的。这里有一点需要注意的是systemPort这个参数，appium server最终与bootstrap建立的socket连接的端口就是它，现在传进来的就是

var UiAutomator = function (adb, opts) {
  this.adb = adb;
  this.proc = null;
  this.cmdCb = null;
  this.socketClient = null;
  this.restartBootstrap = false;
  this.onSocketReady = noop;
  this.alreadyExited = false;
  this.onExit = noop;
  this.shuttingDown = false;
  this.webSocket = opts.webSocket;
  this.systemPort = opts.systemPort;
  this.resendLastCommand = function () {};
};

• 往下我们会看到nodejs流程控制类库async的另外一个对象series，这个有别于上面用到的queue，因为queue时按照worker的数量来看同时执行多少个task的，而series时完全按顺序执行的，所以叫做series
• 这个series 要做的事情就多了，主要就是真正运行时的环境准备，比如检查目标及其api的level是否大于17，安装测试包，bootstrap端口转发，开始测试目标app等，如果每个都进行分析的话大可以另外开一个系列了。这个不是不可能，今后看我时间吧，这里我就分析跟我们这个小节密切相关的uiautomator.start这个方法，其实其他的大家大可以之后自行分析。

    this.uiautomator.start.bind(this.uiautomator),

UiAutomator.prototype.start = function (readyCb) {
  logger.info("Starting App");
  this.adb.killProcessesByName('uiautomator', function (err) {
    if (err) return readyCb(err);
    logger.debug("Running bootstrap");
    var args = ["shell", "uiautomator", "runtest", "AppiumBootstrap.jar", "-c",
        "io.appium.android.bootstrap.Bootstrap"];

    this.alreadyExited = false;
    this.onSocketReady = readyCb;

    this.proc = this.adb.spawn(args);
    this.proc.on("error", function (err) {
      logger.error("Unable to spawn adb: " + err.message);
      if (!this.alreadyExited) {
        this.alreadyExited = true;
        readyCb(new Error("Unable to start Android Debug Bridge: " +
          err.message));
      }
    }.bind(this));
    this.proc.stdout.on('data', this.outputStreamHandler.bind(this));
    this.proc.stderr.on('data', this.errorStreamHandler.bind(this));
    this.proc.on('exit', this.exitHandler.bind(this));
  }.bind(this));
};

UiAutomator.prototype.outputStreamHandler = function (output) {
  this.checkForSocketReady(output);
  this.handleBootstrapOutput(output);
};

UiAutomator.prototype.checkForSocketReady = function (output) {
  if (/Appium Socket Server Ready/.test(output)) {
    this.socketClient = net.connect(this.systemPort, function () {
      this.debug("Connected!");
      this.onSocketReady(null);
    }.bind(this));
    this.socketClient.setEncoding('utf8');
    ...
  }
};

uiautomator runtest AppiumBootstrap.jar -c io.appium.android.bootstrap.Bootstrap

    this.socketClient = net.connect(this.systemPort, function () {

4. 往Bootstrap发送命令

info: --> POST /wd/hub/session/ae82c5ae-76f8-4f67-9312-39e4a52f5643/element/2/click {"id":"2"}

rest.post('/wd/hub/session/:sessionId?/element/:elementId?/click', controller.doClick);

• sessionId：ae82c5ae-76f8-4f67-9312-39e4a52f5643
• elementId: 2

exports.doClick = function (req, res) {
  var elementId = req.params.elementId || req.body.element;
  req.device.click(elementId, getResponseHandler(req, res));
};

req.device = appium.device;

...
, androidController = require('./android-controller.js')
...
_.extend(Android.prototype, androidController);

androidController.click = function (elementId, cb) {
  this.proxy(["element:click", {elementId: elementId}], cb);
};

exports.proxy = function (command, cb) {
  logger.debug('Pushing command to appium work queue: ' + JSON.stringify(command));
  this.push([command, cb]);
};

Android.prototype.initQueue = function () {
  this.queue = async.queue(function (task, cb) {
    var action = task.action,
        params = task.params;

    this.cbForCurrentCmd = cb;

    if (this.adb && !this.shuttingDown) {
      this.uiautomator.sendAction(action, params, function (response) {
        this.cbForCurrentCmd = null;
        if (typeof cb === 'function') {
          this.respond(response, cb);
        }
      }.bind(this));
    } else {
      this.cbForCurrentCmd = null;
      var msg = "Tried to send command to non-existent Android device, " +
                 "maybe it shut down?";
      if (this.shuttingDown) {
        msg = "We're in the middle of shutting down the Android device, " +
              "so your request won't be executed. Sorry!";
      }
      this.respond({
        status: status.codes.UnknownError.code
      , value: msg
      }, cb);
    }
  }.bind(this), 1);
};

• action:"element:click"
• params:"{elementId:2"}

UiAutomator.prototype.sendAction = function (action, params, cb) {
  if (typeof params === "function") {
    cb = params;
    params = {};
  }
  var extra = {action: action, params: params};
  this.sendCommand('action', extra, cb);
};

• 参数1:‘action’
• 参数2:‘{action:action,parames:{elementId:2}‘

UiAutomator.prototype.sendCommand = function (type, extra, cb) {
    ...
 else if (this.socketClient) {
    ...
    var cmd = {cmd: type};
    cmd = _.extend(cmd, extra);
    var cmdJson = JSON.stringify(cmd) + "\n";
    this.cmdCb = cb;
    var logCmd = cmdJson.trim();
    if (logCmd.length > 1000) {
      logCmd = logCmd.substr(0, 1000) + "...";
    }
    this.debug("Sending command to android: " + logCmd);
    this.socketClient.write(cmdJson);
  } 
    ...
}

• {"cmd":"action","action":element:click","params":{"elementId":"2"}}

5. 小结

• 初始化REST路由表来接收appium client过来的REST命令调用并分发给相应的controller方法来进行处理
• appium client发送命令之前会先触发一个创建session的请求，在路由表表现为“rest.post(‘/wd/hub/session‘, controller.createSession);”。对应的controller处理方法会开始初始化与bootstrap的连接
• 创建的session的过程会调用Appium类的start方法然后机型一系列的动作：
  • 初始化设备类Android
  • 用Async库的queue对象初始化Appium的Work Queue
  • 创建adb实例并启动adb
  • 安装测试apk
  • 通过adb启动bootstrap
  • 建立Appium Server和bootstrap的socket连接
  • ...,等等等等
• 创建好连接后Appium Server就会接收client过来的命令，比如click，然后对应的controller处理方法就会建立命令对应的task并把它push到async queue里面
• 一旦有新task进入到async queue，对应的回调函数就会触发，开始往已经建立的与bootstrap的socket连接发送json字串命令