Ensure res is defined before calling res.resume()

[alexmuller]

My colleague Cynthia noticed this recent change to the plugin.

In production we are seeing multiple apps crashing because res is undefined.

This is a speculative fix which probably needs more work from someone who knows a lot more about this plugin than me.

We have ticket 1324529 open for this issue.

[alexmuller]

This was introduced recently in #112 - @thebanjomatic @colincasey is it possible that res can be undefined here?

We're seeing unhandled errors with the stack:

TypeError: Cannot read properties of undefined (reading 'resume')
    at ClientRequest.<anonymous> (/app/.heroku/heroku-nodejs-plugin/index.js:99:11)
    at ClientRequest.emit (node:events:517:28)
    at ClientRequest.emit (node:domain:489:12)
    at TLSSocket.socketErrorListener (node:_http_client:501:9)
    at TLSSocket.emit (node:events:517:28)
    at TLSSocket.emit (node:domain:489:12)
    at emitErrorNT (node:internal/streams/destroy:151:8)
    at emitErrorCloseNT (node:internal/streams/destroy:116:3)
    at process.processTicksAndRejections (node:internal/process/task_queues:82:21)

[apaleslimghost]

i think the correct fix here is to move the res.resume(); to after the err != null check. the callback is called with just the error from the res error handler which is why res is undefined here.

[colincasey]

@apaleslimghost I agree, it would be better to move the logic to after err is checked but the code here will correctly prevent res.resume() from being called when res is undefined which is the main issue.

If I was planning on continuing maintenance on this plugin I would demand a bit more here but I'm currently trying to get this plugin retired and replaced with equivalent metrics using Node's Performance APIs instead of this C++ addon.

Thanks for reporting this @alexmuller. Apologies for not catching this when reviewing #112. This plugin has to be tested manually and I did not hit that edge case while verifying that the memory leak was fixed.

[colincasey]

@alexmuller this fix is included in the v231 release of the heroku/nodejs buildpack. Redeploying your application(s) should address the crashes you're experiencing.

[alexmuller]

Thanks for fixing this so quickly @colincasey!