JS transformation to encode JSON in HTTP binding

Add-ons Bindings
,
1

Happy (almost) New Year from the Southern Hemisphere!!

I am trying to use the HTTP binding to send this to a webserver:
{"DA":{"tempTarget":25.5}

where the target temperature is a variable and linked to an item. I know that I can have a MAP with individual lines such as:
22={"DA":{"tempTarget":22}}
and while this works, it seems inefficient.

On advice from a different post Help MAP transformation with HTTP Binding OH3
I came up with this bit of code (PS not a programmer at all) and put it in actron_tempTarget.js in the transformation folder, however after triggering the dial connected to the item, nothing happens. The JS transformation is installed.

(function transformValueToJson(i) { 
    var obj = { DA: {tempTarget: i }};
    return (JSON.stringify(obj));
})(input);

The Command Transformation setting on the channel is coded as:
JS:actron_tempTarget.js

Just wondering what I am doing wrong? Can anyone help?

2
Presumably this could be something like: 
var obj = "{ \"DA\": {\"tempTarget\": \"" +i+ "\" }}";

And then just return obj

3

Thanks for your very quick reply. Unfortunately it didnā€™t work. The response in the logs was:
{{"result":0,"error":"Unknown Request","id":400,"data":null}}

My version gets me
{{"result":1,"error":null,"id":0,"data":null}}

4

Yeah, youā€™re right - apologies, got my wires crossed. Not sure why yours isnā€™t working. What logs are you copying those responses from?

5

Sorry the ā€œunknown requestā€ response from the log happened because I didnā€™t use your entire suggestion. Once I changed to return obj; i get the same result of {{"result":1,"error":null,"id":0,"data":null}}

I am getting this from the log in karaf. should I look someplace else?

6

I have a hunch: remove the function name and trailing semicolon:

(function(i) { 
    var obj = { DA: {tempTarget: i }};
    return (JSON.stringify(obj));
})(input)
7

No dice sadly. I removed the function name and semicolon from both versions (my original and your suggestion)

8

Then Iā€™m out of ideas, sadly! As I understand it the JS transformation service looks for the ā€˜masterā€™ function in a file, which is one without a name.

Perhaps try simplifying your rule so all it does is return ā€œhelloā€ and see what it does?

9

No worries. Thanks so much for the suggestions.

10

Ok I worked it out.

I tried the suggestion of returning ā€œhelloā€ but I couldnā€™t see this represented anywhere in the logs. It turns out I had changed the logging level of org.openhab.binding.http.internal.http to TRACE but it was only giving me part of the picture. On a hunch I set org.openhab.binding.http to TRACE and could then see the outgoing stuff.

In doing this, I noticed that the temperature value was being sent as a string Content = {{"DA":{"tempTarget":"31"}}} (I think thatā€™s the correct interpretation). Anyway I changed the code in the transformation to convert the string value to a number first before compiling the response and it is now working. The complete code is below:

(function (i) { 
    var tempValue = parseFloat(i)
    var obj = { DA: {tempTarget: tempValue }};
    return (JSON.stringify(obj));
})(input)

Not sure if this is how it ā€œshould beā€ done or whether the configuration in the UI should have been changed instead, but in any event it is working correctly now.

Thanks @hafniumzinc for your input on solving this.

2 Likes
11

Ah, crap, yes - the JS transformation input only deals in strings. I should have spotted that - apologies! Glad youā€™ve got it working!

12

No worries. Donā€™t be sorry. It was a good puzzle to solve and Iā€™ve started the new year feeling like Iā€™ve accomplished something already

13

Hey @Lukie Iā€™m only just embarking on the migration of my Actron over to the new OH3. HTTP 3.x certainly is different.

14

Yeah it took a while and I needed some help but I got it to work. This thread documents my progress is getting it to work:
https://community.openhab.org/t/help-map-transformation-with-http-binding-oh3/109213/14

Shout out if you still have trouble and Iā€™ll help where I can

2 Likes
15

Hi Lucas,
I am trying to get a JSON string also send via HTTP.
My challenge is, as shown here that the JSON string actually includes multiple components.
I know how to handle simple JSON strings and read values via GET, but the POST command with multiple components is still a black box for me.
Any advice on how this could work of it is even possible?
Thanks!

EDIT: I figured it out thanks to your post! map transformation to the rescue :slight_smile:

1 Like
16

Glad you figured it out. It took me ages to get it to work and I needed help in the end.