fix(output): ignore stdio channels (stdout, stdin, stderr)

[wardpeet]

Add { stdio: 'ignore' } to execFileSync to make sure no output is generated to our output buffers.

fixes GoogleChrome/lighthouse#5795

[wardpeet]

@paulirish whenever you have the time 😄

[paulirish]

tbh i can't reproduce the bug on mac or my ubuntu, but i don't see why this wouldn't work.

@wardpeet did you repro it?

[wardpeet]

yes I did but only in docker so I guess it has to do with docker piping all output to the docker logs command

[ghost]

The modified line tries to parse the output of the executed command. { stdio: 'ignore' } redirects the output to /dev/null, completely breaking that.

[wardpeet]

Sorry what are you referring to? What does it break?

[ghost]

The line modified by the commit 35842ba:
execFileSync('which', [executable], {stdio: 'ignore'}).toString().split(newLineRegex)[0];

.toString() can't return anything if stdout is ignored.

[wardpeet]

I'll create a fix

[paulirish]

aye. just tested this and looks like @vpracht is right. Thx very much for commenting!

my repro:

// log.js
process.stdout.write('STDOUT\n');

process.stderr.write('stderr\n');

// index.js
const {execFileSync} = require('child_process');

const output = execFileSync('node', ['log.js'], {encoding: 'utf-8', stdio: 'ignore'});

console.log({output});

node index.js
# { output: null }

---

@wardpeet looks like 'stdio':'pipe' is what we want? also i don't know how this worked without utf-8 before, but it seems necessary to avoid getting a buffer.

[wardpeet]

yeah I just tested it in docker too and pipe works as well. The reason why I thought it wouldn't was because I thought the default was pipe as stated in the docs but I missed the following line

Child's stdio configuration. stderr by default will be output to the parent process' stderr unless stdio is specified. Default: 'pipe'.

[wardpeet]

@vpracht fix is up #125

[paulirish]

fixed in chrome-launcher@0.10.5