[Feature Request] Piping stdout from child process into main process

[derN3rd]

While working with sub-process workers (sandboxed job processors) I tried to find a good way to get debug information within the job code and in general from the process. (Same as #1021)

The easiest way I came up with is to patch the lib/process/child-pool.js with:

@@ -4,7 +4,6 @@
@@ -4,6 +4,7 @@
 const path = require('path');
 const _ = require('lodash');
 const getPort = require('get-port');
+const { Transform } = require('stream');
 
 const ChildPool = function ChildPool() {
   if (!(this instanceof ChildPool)) {
@@ -47,8 +48,21 @@
 
   return convertExecArgv(process.execArgv).then(execArgv => {
     child = fork(path.join(__dirname, './master.js'), {
-      execArgv
+      execArgv,
+      stdio: 'pipe',
     });
+
+    // main folder that includes the node_modules
+    const projectFolder = __dirname.split('node_modules/').shift()
+    const readableProcessName = processFile.replace(projectFolder, '')
+
+    const processNamePrependTransform = new Transform({
+      transform: (chunk, encoding, done) => {
+          const result = `[${readableProcessName}] ${chunk.toString()}`
+          done(null, result)
+      }
+  })
+
+    child.stdout.pipe(processNamePrependTransform).pipe(process.stdout);
+    
     child.processFile = processFile;

this will pipe any child stdout into the main process stdout with its processFile (e.g. [src/jobs/processImage.js] found invalid image file '/tmp/x.png'). (Obviously the transform part is not needed and only adds from which process the output came. This could also be extended with the process pid etc)

I think this could be useful for other people as well e.g. behind a config or environment flag.

As I didn't work with fork before I don't know about negative side effects for this in production environments, but in my local dev setup it worked and helped me a lot already.

[phips28]

I like this idea, that would also support pm2 logs then

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[derN3rd]

Don't you dare to close a Feature Request, Stale Bot 🧐

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[bugs181]

This is a nifty trick. I solved it a different way by using Event hooks.

rsyncQueue.process(function(job, done) {
  const rsync = new Rsync(job.data)
  rsync.on('log', (message) => job.log(message))`
})

Then inside the Rsync class:

class Rsync extends EventEmitter {
  ...
  child.stdout.on('data', (dataObj) => {
     const data = dataObj.toString()
     this.emit('log', data)
  }
}

[TheArhaam]

Have there been any developments on this? I would much rather have this coming from the package itself than have to set up some custom config for handling the logs