Cannot read properties of undefined (reading 'Header') about ladder99

[bburns]

Hey Hector, thanks a lot for tracking this down! My guess is that one of your agents is returning HTML instead of XML for some reason, as this indicates -

{ html: { head: { title: [Object] }, body: { center: [Object] } } }

I added some more error handling, and had the fetch method loop until it gets a valid looking agent response -

  async fetchJsTree(type, from, count) {
    const url = this.getUrl(type, from, count)
    let jsTree
    do {
      try {
        const response = await fetch(url)
        const xml = await response.text() // try to parse response as xml
        jsTree = convert.xml2js(xml, convertOptions) // try to convert to js tree
        // make sure we have a valid agent response
        if (
          !jsTree.MTConnectDevices &&
          !jsTree.MTConnectStreams &&
          !jsTree.MTConnectError
        ) {
          throw new Error(
            'Invalid agent response - should have MTConnectDevices, MTConnectStreams, or MTConnectError.'
          )
        }
      } catch (error) {
        // error.code could be ENOTFOUND, ECONNREFUSED, EHOSTUNREACH, etc
        console.error('Relay error', error)
        console.log(`Relay error reading`, url)
        console.log(`Relay jsTree:`)
        console.dir(jsTree, { depth: 3 })
        console.log(`Relay error retrying in ${waitTryAgain} ms...`)
        await lib.sleep(waitTryAgain)
        jsTree = null // so loop again
      }
    } while (!jsTree)
    return jsTree
  }

Hopefully that will be more robust. It's there if you'd like to give it a try - just do git pull in the ladder99/ladder99 folder.

[hlopez5]

Diving into the problem

Identification

Diving into the exact line on the data.js script it seems like the following is the key code snippet that is causing the error.

// get Header attributes for probe, current, or sample xmls.
    // includes { instanceId, firstSequence, nextSequence, lastSequence, bufferSize, ... }
    this.header = this.jsTree.MTConnectDevices
      ? this.jsTree.MTConnectDevices.Header._
      : this.jsTree.MTConnectStreams.Header._

Javascript ternary operator :
condition ? exprIfTrue : exprIfFalse

This line seems to try to check the object MTConnectDevices is not null and set the header to MTConnectDevices if not set it to MTConnectStreams.

I added a console.log to the script and found out that the console.log(this.jsTree.MTConnectDevices) is outputting undefined

Seems like this is not really a header issue but a problem parsing out an endpoint.

Going Deeper

I exposed the entire this.jsTree in the console and started looking at a pattern. After some endpoints I was able to get a successful response of the object. Note: I hid my uuid, host and port information.

Relay warning: the following devices have no alias - could add in setup.yaml.

Alias missing for device

db upsert node **{uuid}**/device: **{uuid}**/device
{
  MTConnectDevices: {
    _: {
      'xmlns:m': 'urn:mtconnect.org:MTConnectDevices:1.5',
      xmlns: 'urn:mtconnect.org:MTConnectDevices:1.5',
      'xmlns:xsi': 'http://www.w3.org/2001/XMLSchema-instance',
      'xsi:schemaLocation': 'urn:mtconnect.org:MTConnectDevices:1.5 /schemas/MTConnectDevices_1.5.xsd'
    },
    Header: { _: [Object] },
    Devices: { Device: [Object] }
  }
}

Then shortly after another output from the relay log shows the error propping up right after a not so verbose log output.

Relay warning: the following devices have no alias - could add in setup.yaml.

Alias missing for device

db upsert node **{uuid-2}**/device: **{uuid-2}**/device
{ html: { head: { title: [Object] }, body: { center: [Object] } } }

db signal uncaughtException received - shutting down...
TypeError: Cannot read properties of undefined (reading 'Header')
    at Probe.read (file:///usr/app/src/data.js:48:38)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async Probe.read (file:///usr/app/src/dataProbe.js:18:5)
    at async AgentReader.start (file:///usr/app/src/agentReader.js:48:7)

Summary

After noticing that the endpoints for both agents where nearly identical the issue may lie elsewhere in the endpoint collection methods. The fix I would propose is to return a handled exception instead of an unhandled exception that stops the relay service all together. I added the following to the data.js file to handle the error :

 if (this.jsTree.MTConnectDevices == undefined) {
      console.log(this.jsTree)
      console.log("TypeError: Cannot read properties of undefined (reading 'Header')")
      return false
    }

   // get Header attributes for probe, current, or sample xmls.
   // includes { instanceId, firstSequence, nextSequence, lastSequence, bufferSize, ... }
    this.header = this.jsTree.MTConnectDevices
      ? this.jsTree.MTConnectDevices.Header._
      : this.jsTree.MTConnectStreams.Header._

Welp... That didnt work

Caught a nice error in the face with that last idea. Looks like the best thing to do is prob a bunch of conditionals everywhere
... I ended up sticking some variation of the following in the agentReader.js do/while loops.

if ( {insert object from error} == undefined) { continue;} 

[hlopez5]

Awesome! I wouldnt know how the agent is sending html instead of a valid xml. I wonder if it has something to do with the agent 2.0 "agent-adapter" that we have been testing.

[bburns]

Can you see what that agent shows in the browser?

[MRIIOT]

@hlopez5 has this been resolved?