problem getting device id in callback

[palsbo]

When I want to issue a serie of reads to several devices, the callback gives no way of telling which device is delivering result.
What to do?

var Client = require("owfs").Client;
var con = new Client('localhost');

var dev = [
        {'id':'/10.243EE400080086/temperature', 'topic':'/lolland/stuen'},
        {'id':'/10.8E6521010800E3/temperature', 'topic':'/lolland/vaerksted'},
        {'id':'/10.FD622101080073/temperature', 'topic':'/lolland/orangeri'},
        {'id':'/10.AFCE3503080058/temperature', 'topic':'/lolland/depot'},
]

for (i in dev) {
        con.read(dev[i].id, function(err, result) {
               console.log(dev[i].id,dev[i].topic, result);  //  this will not work!
        });
}

[njh]

Hi,

You say "this will not work" - does it not work?
Or do you just think it won't won't?

I think it should work - in JavaScript dev[i].topic should be in scope within that callback.

It probably doesn't help, because it is a bit complex but this is the code I wrote that uses the owfs.js library:

https://github.com/njh/node-red-contrib-owfs/blob/master/owfs.js

nick.

[njh]

I havn't tested it but something like this should work:

function lookupTemp(hostname, path) {

    var Client = require('owfs').Client
    var client = new Client(hostname, 4304)

    client.read(path, function (err, result) {
        if (err) {
            console.log(err)
        } else {
            console.log("path: " + path)
            console.log("result: " + result)
        }
    })

}

[palsbo]

No it does not work!. It works for one device, but when issuing read for several devices, the path in the callback will be the last used path - for all events. The path must be delivered as an argument in the callback to identify the path.

[njh]

Would it help you if I created a working example?

[palsbo]

See this example:

var Client = require('owfs').Client
var client = new Client('localhost', 4304)

var dev = [
	{'id':'/10.243EE400080086/temperature', 'topic':'/lolland/stuen'},
	{'id':'/10.8E6521010800E3/temperature', 'topic':'/lolland/vaerksted'},
	{'id':'/10.FD622101080073/temperature', 'topic':'/lolland/orangeri'},
	{'id':'/10.AFCE3503080058/temperature', 'topic':'/lolland/depot',},
]

function lookupTemp(path) {
    client.read(path, function (err, result) {
        if (err) {
            console.log(err)
        } else {
            console.log("path: " + path)
            console.log("result: " + result)
        }
    })
}
for (i in dev) {
	lookupTemp(dev[i].id);
}

The result is (correct!);

path: /10.243EE400080086/temperature
result: 19.1875
path: /10.FD622101080073/temperature
result: 16.375
path: /10.8E6521010800E3/temperature
result: 16.5625
path: /10.AFCE3503080058/temperature
result: 19.875

Then changing the code like this:

var Client = require('owfs').Client
var client = new Client('localhost', 4304)

var dev = [
	{'id':'/10.243EE400080086/temperature', 'topic':'/lolland/stuen'},
	{'id':'/10.8E6521010800E3/temperature', 'topic':'/lolland/vaerksted'},
	{'id':'/10.FD622101080073/temperature', 'topic':'/lolland/orangeri'},
	{'id':'/10.AFCE3503080058/temperature', 'topic':'/lolland/depot',},
]


for (i in dev) {
	var path = dev[i].id;
    client.read(path, function (err, result) {
        if (err) {
            console.log(err)
        } else {
            console.log("path: " + path)
            console.log("result: " + result)
        }
    })
}

The result is (I expected a duplication of the old result):

path: /10.AFCE3503080058/temperature
result: 19.1875
path: /10.AFCE3503080058/temperature
result: 16.625
path: /10.AFCE3503080058/temperature
result: 19.875
path: /10.AFCE3503080058/temperature
result: 16.25

```

Results are correct, buit path is duplicated.
I understand that this is async code. This is why you cannot count on the initial values in the callback.