Blockingproxy: TypeError: Cannot read property 'toString' of null

[rodrigc]

Originally reported here: angular/protractor#4473

I have been using some protractor scripts which have been running fine for a few months.

In the past week, I upgraded to:

• Node Version: v8.4.0
• Protractor Version: version 5.1.2
• Browser(s): Chrome 61.0.3163.79
• Chromedriver: 2.32
• selenium standalone server: 3.5.3
• Operating System and Version MacOS X and Windows

and suddenly I am getting this error in BlockingProxy:

BlockingProxy error: E/BlockingProxy - (node:26020) TypeError: Cannot read property 'toString' of null

I added the node --trace-warnings flag and got a stack trace:

 E/BlockingProxy - (node:26296) TypeError: Cannot read property 'toString' of null
    at replyWithError (/Users/c-craigr/work1/es-automation-test/ui-tests/node_modules/blocking-proxy/built/lib/webdriver_proxy.js:42:35)
    at WebDriverProxy.<anonymous> (/Users/c-craigr/work1/es-automation-test/ui-tests/node_modules/blocking-proxy/built/lib/webdriver_proxy.js:53:17)
    at Generator.throw (<anonymous>)
    at rejected (/Users/c-craigr/work1/es-automation-test/ui-tests/node_modules/blocking-proxy/built/lib/webdriver_proxy.js:5:62)
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:188:7)

I tracked the problem down to this code in BlockingProxy:

https://github.com/angular/blocking-proxy/blob/master/lib/webdriver_proxy.ts#L29

 let replyWithError = (err) => {
      response.writeHead(500);
      response.write(err.toString());
      response.end();
    };

In this case err is null, so that causes an exception to be thrown.

Does anybody have an idea why err is null?

[rodrigc]

The problem seems to be in BlockingProxy, which is available in Protractor 5.1.0 and higher.
Disabling BlockingProxy made things work for me.
I put this in my exports.config:

useBlockingProxy: false

and removed the webDriverLogDir setting.

[rodrigc]

Similar problem reported here: angular/protractor#4448

[rodrigc]

In the past month, I noticed that there have been new releases of:

• Chromedriver: 2.32 ( https://sites.google.com/a/chromium.org/chromedriver/downloads )
• Selenium Standalone Server: 3.5.3 ( http://www.seleniumhq.org/download/ )

I'm not sure, but maybe the Selenium Standalone Server is communicating errors
in a different way to the BlockingProxy, thus triggering this error.

[heathkit]

Thanks, sorry about this. Yes, the issue is protocol changes in selenium standalone server 3.5.x. I have a fix on the way, but it won't get picked up until the next Protractor release.

[rodrigc]

@heathkit thanks