Occasional "Symbol not found"

[acidos]

I have an app which is periodically writing few variables in PLC. The period is every 5 minute.

var options = {
    host: "127.0.0.1",
    amsNetIdTarget: "10.10.2.100.1.1",
    amsNetIdSource: "10.10.2.100.1.15",
    amsPortTarget: 801
}

var client = ads.connect(options, function() {
                    WriteAds(client, values[0]).
                    then(() => WriteAds(client, values[1])).
                    then(() => WriteAds(client, values[2])).
                    then(() => WriteAds(client, values[3])).
                    then(() => WriteAds(client, values[4])).
                    then(() => WriteAds(client, values[5])).
                    then(() => WriteAds(client, values[6])).
                    then(() => WriteAds(client, validityHandle)).
                    catch((err) => { 
                        log.error("Error writing to ADS: ", err);
                    }).
                    finally(() => ReleaseAndDisconnect(client))
                })

function ReleaseAndDisconnect(client)
{
    return new Promise(function(resolve, reject){
        client.end(function (){ resolve() })
        resolve()
    })
}

function WriteAds(client, h)
{
    return new Promise(function(resolve, reject){
        client.write(h, function(err) {
            if (err) 
            {
                reject(err)
            }
            else
            {
                resolve()
            }
        })
    })
}

As you can see, there are 6 handles in array and 1 standalone handle. This is the exception

Error writing to ADS: symbol not found
Error: symbol not found
    at getError (C:\pkg\node_modules\node-ads\lib\ads.js:1290:13)
    at Object.getWriteResult (C:\pkg\node_modules\node-ads\lib\ads.js:792:13)
    at Object.analyseResponse (C:\pkg\node_modules\node-ads\lib\ads.js:224:24)
    at Object.checkResponseStream (C:\pkg\node_modules\node-ads\lib\ads.js:177:25)
    at Socket.<anonymous> (C:\pkg\node_modules\node-ads\lib\ads.js:116:25)
    at emitOne (events.js:116:13)
    at Socket.emit (events.js:211:7)
    at addChunk (_stream_readable.js:263:12)
    at readableAddChunk (_stream_readable.js:250:11)
    at Socket.Readable.push (_stream_readable.js:208:10)

It happens on standalone variable. Variables before are written just fine.

I captured ADS traffic and can see that ADSIGRP_SYM_HNDBYNAME is called for all variables following ADSIGRP_SYM_VALBYHND, except last one. The last one only received ADSIGRP_SYM_VALBYHND without prior ADSIGRP_SYM_HNDBYNAME. Not sure where index/offset was discovered, but there is some value. Is it cached somewhere?

[PLCHome]

Global symname must start with a dot: .engine, program symname must start with the programname: MAIN.UpTyp.timerUp.PT.

There is also a problem with special characters, because node-ads pass the texts as UTF8 to the PLC and not as ASCII. Do you want to tell us the symname name?

You can use getSymbols to trace the known names.

client = ads.connect(options, function() {
    this.getSymbols(function(err, symbols) {
        if (err) console.log(err)
        console.log(symbols)
        this.end()
    })
})

---

        client.end(function (){ resolve() })
        resolve()

better you remove the second resolve() ;-)

[acidos]

This is the failing handle

var validityHandle = {
    symname: 'MAIN.PKG.bEnable',
    bytelength: ads.BOOL,  
    propname: 'value',
    value: true
}

The successful ones are MAIN.PKG.BLA_BLA matching exactly to the ones declared in PLC. The type of others are mixed, including float, bool, though I don't think it's related. As I stated, the error "symbol not found" happens occasionally, but with some pattern. If I just start my node app, first(or first few) times everything is successful. The program is running on setInterval of 5 minutes. On consequent timer events, the exception occurs.

[acidos]

better you remove the second resolve() ;-)

ah, dankeschön :)

[acidos]

So what I tried is moved then(() => WriteAds(client, validityHandle)). to the top, to see if the failure is related to the last Write, but it failed again on exactly this handle. If something wrong with the name of the handle, why it's writing successfully always very first time?

[PLCHome]

I think the second resolve() is not the problem here.

I am puzzled about:

_The last one only received ADSIGRP_SYM_VALBYHND without prior ADSIGRP_SYMHNDBYNAME.

node-ads has a peculiarity, it writes all information into the transferred object validityHandle. ADSIGRP_SYM_HNDBYNAME is not called when a handle is handed over. But then the symname is forbidden. I am confused

[acidos]

So I have bunch of ADSIGRP_SYM_HNDBYNAME calls like below for all handles in values array:

Then all of the sudden I see ADSIGRP_SYM_VALBYHND to read the value for bEnable I guess, not sure where it got index/offset:

Then an error:

Tomorrow I'm going to do getSymbols, to see if the index/offset is matching. Second, I'm going to capture the first successful operation and compare.

[acidos]

I did a quick capture of successful call and I see ADSIGRP_SYM_HNDBYNAME

[PLCHome]

this is a part of var getHandle = function

    if (typeof handle.symhandle === 'undefined') {
      var commandOptions = {
        indexGroup: ADSIGRP.GET_SYMHANDLE_BYNAME,
        indexOffset: 0x00000000,
        writeBuffer: buf,
        readLength: 4,
        symname: handle.symname
      }

      writeReadCommand.call(ads, commandOptions, function (err, result) {
      .....
}

plase try only for a test:

function WriteAds(client, h)
{
    return new Promise(function(resolve, reject){
        client.write(h, function(err) {
           delete(h.symhandle)
           if (err) 
            {
                reject(err)
            }
            else
            {
                resolve()
            }
        })
    })
}

or use a clean object:

function WriteAds(client, h)
{
    return new Promise(function(resolve, reject){
        var newH = Object.assign({},h)
        client.write(newH, function(err) {
           if (err) 
            {
                reject(err)
            }
            else
            {
                resolve()
            }
        })
    })
}

because client.end releases all symhandle you got in the session

var end = function (cb) {
 ...
  releaseSymHandles.call(ads, function () {
   ...

Did you slove the connection problem on the localhost?

[acidos]

So you mean the old value of symhandle is persisting through the multiple calls? Can be true, because only that object is static and I never reset it. I'll try it tomorrow morning, off to bed now. Thanks!

[PLCHome]

So you mean the old value of synhandle is persisting through the multiple calls?

yes that's javascript

[PLCHome]

If I look at the code, it looks like you would pick up a value via http-get and send it to the PLC. Ever thought about NODE-RED?

Timer Node -> HTTP Request Node -> ADS Write Node

[acidos]

Did you slove the connection problem on the localhost?

I'll update previous topic in a moment

[acidos]

If I look at the code, it looks like you would pick up a value via http-get and send it to the PLC. Ever thought about NODE-RED?

Timer Node -> HTTP Request Node -> ADS Write Node

My web request is pretty complex and requires login, cookies, cheerio, header case normalization to extract data. The function is already there(around 200 lines of code) and I'm not sure if I can easily do it with HTTP Request Node.

Also for ADS I need to write float values, extracted from the web, then at the end put validity flag, before invalidation timer expires in PLC. Not sure if this can be achieved in NR as flexible as I do it in single js file.

Currently I installed it as windows service, using node-windows and it's running smoothly. Thanks to you, the problem with symbol not found solved (though I think lib should not keep the state in user object).

With that said, I love NR and always looking for opportunities to use it. But for this task it feels like shooting bird with canon.

[PLCHome]

Thanks to you, the problem with symbol not found solved

Added note in the readme.md @roccomuso please close

[roccomuso]

ok thanks!