Prevent runtime errors. [Solved]

[Hesitated]

I've been working with customEvents and it is helpfull to reduce (duplicate) code in other scripts, so they will be easier to maintain.

E.g.:

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local up = "Up"
local down = "Down"

return {
  on = {
    customEvents = {
      'BedieningRolluiken'
    }
  },
  logging = 
  { 
    level = domoticz.LOG_ERROR,
    marker = "Bediening rolluiken" 
  },
  execute = function(dz, item)

    local function rolluikOpen(rolluik)
      if rolluik ~= nil then
        dz.log('Rolluik omhoog: ' .. rolluik.name, dz.LOG_DEBUG)
        rolluik.switchOff()
      end
    end

    local function rolluikDicht(rolluik)
      if rolluik ~= nil then
        dz.log('Rolluik omlaag: ' .. rolluik.name, dz.LOG_DEBUG)
        rolluik.switchOn()
      end
    end

    local json = dz.utils.fromJSON(item.data)
    local command = json[1]
    
    if command ~= up and command ~= down then
       return 
    end

    local devices = json[2]
    local rolluiken = dz.devices().filter(devices)
    dz.log('#rolluiken: ' .. tostring(#rolluiken), dz.LOG_DEBUG)

    if command == up then
      dz.log('Command was "Up"', dz.LOG_DEBUG)
      rolluiken.forEach(function(rolluik)
        rolluikOpen(rolluik)
      end)
    elseif command == down then
      dz.log('Command was "Down"', dz.LOG_DEBUG)
      rolluiken.forEach(function(rolluik)
        rolluikDicht(rolluik)
      end)
    end
  end
}

Which will be triggered by other scripts containing:

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  local args = {
    "Down",
    idsRolluiken
  }
  dz.emitEvent('BedieningRolluiken', args)

But the main script could fail when the passed arguments are not in the expected format.
E.g.:

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local json = dz.utils.fromJSON(item.data)

could fail if item.data is not (proper) json

Or:

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local rolluiken = dz.devices().filter(devices)

could fail if devices are not found.

How do I prevent these runtime errors? (pcall can't be used here)

[boum]

Why would pcall couldn't be called there? What behavior do you expect?

You can protect against runtime error either piecemeal or on the whole custom event script.
For the two places you shown, it would be:

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local ok, json = pcall(dz.utils.fromJSON, item.data)
if not ok then 
  -- handle error
  return
end

and

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-- use anonymous function, dz.devices() is a table
local ok, rolluiken = pcall(function() return dz.devices().filter(devices) end) 
if not ok then 
  -- handle device not found
  return
end

and for the custom script, you just wrap your whole execute function in a local function and pcall it:

Code: Select all

return {
  on = {
    customEvents = { 'BedieningRolluiken' }
  },
  execute = function(dz, item)
    local checkExecute = function(dz, item)
      local function rolluikOpen(rolluik) [...]
      end
      [...]
    end
    
    -- protected call
    local ok = pcall(checkExecute, dz, item)
    if not ok then
      dz.log(...)
    end
  end
}

[boum]

I checked and you cannot use pcall on callable tables. I'll update the example above for dz.devices.

[Hesitated]

Why would pcall couldn't be called there? What behavior do you expect?

I think my knowledge of lua is still far too limited...

Code: Select all

local ok, json = pcall(dz.utils.fromJSON, item.data)

Ah, I did not know that I could put json as the second variable.

and for the custom script, you just wrap your whole execute function in a local function and pcall it:

This one I should have known, but didn't think of it.

[waaren]

But the main script could fail when the passed arguments are not in the expected format.
E.g.:

Code: Select all

local json = dz.utils.fromJSON(item.data)

could fail if item.data is not (proper) json

If item.data is not in the right JSON format you will get an error message but the script will not fail. Item.data will be nil and that is something that can be handled in your script logic.

[Hesitated]

If item.data is not in the right JSON format you will get an error message but the script will not fail. Item.data will be nil and that is something that can be handled in your script logic.

Unfortunately not always.

With this url you're right!

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https://domoticz/json.htm?type=command&param=customevent&event=BedieningRolluiken&data=ok

But if you use this url:

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https://domoticz/json.htm?type=command&param=customevent&event=BedieningRolluiken&data=[%22Up%22,{}]

you'll get:

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2020-04-26 17:41:54.697 Error: dzVents: Error: (3.0.1) Bediening rolluiken: Error parsing json to LUA table: /home/pi/domoticz/scripts/dzVents/../lua/JSON.lua:808: expected string argument to JSON:decode(), got table
2020-04-26 17:41:54.697 Error: dzVents: Error: (3.0.1) Bediening rolluiken: item.data is not jsontable: 0x728f4468 

[waaren]

Unfortunately not always.
if you use this url:

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https://domoticz/json.htm?type=command&param=customevent&event=BedieningRolluiken&data=[%22Up%22,{}]

you'll get:

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2020-04-26 17:41:54.697 Error: dzVents: Error: (3.0.1) Bediening rolluiken: Error parsing json to LUA table: /home/pi/domoticz/scripts/dzVents/../lua/JSON.lua:808: expected string argument to JSON:decode(), got table
2020-04-26 17:41:54.697 Error: dzVents: Error: (3.0.1) Bediening rolluiken: item.data is not jsontable: 0x728f4468 

Yes you can get an Error message but the script will continue (at least it does on my systems (dzVents 3.0.2)

Let me have a look if I can add the isJSON attribute to item in customEvents triggers to help catching errors.

If I use

Code: Select all

        /json.htm?type=command&param=customevent&event=faultyJSON&data=[%22Up%22,{}]

and this test script

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return 
{
	on = 
	{
		customEvents = 
		{
			'faultyJSON',  -- just an example to trigger the request
		},
	},
		
	execute = function(dz, item)
        -- /json.htm?type=command&param=customevent&event=faultyJSON&data=[%22Up%22,{}]
        
        lodash = dz.utils._
        
        for i=1, 10 do
            dz.log('although you will see an error. The script is  still executing here', dz.LOG_FORCE)
        end
        
        
        dz.log('ítem is: ' .. lodash.str(item), dz.LOG_FORCE)
        dz.log('item.data: ' .. lodash.str(item.data), dz.LOG_FORCE)
    end	
}

The log shows:

Spoiler: show

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2020-04-26 19:03:24.612 Status: dzVents: Info: Handling Domoticz custom event for: "faultyJSON"
2020-04-26 19:03:24.613 Status: dzVents: Info: ------ Start internal script: dz JSON reader: Custom event: "faultyJSON"
2020-04-26 19:03:24.613 Status: dzVents: !Info: although you will see an error. The script is still executing here
2020-04-26 19:03:24.613 Status: dzVents: !Info: although you will see an error. The script is still executing here
2020-04-26 19:03:24.613 Status: dzVents: !Info: although you will see an error. The script is still executing here
2020-04-26 19:03:24.613 Status: dzVents: !Info: although you will see an error. The script is still executing here
2020-04-26 19:03:24.613 Status: dzVents: !Info: although you will see an error. The script is still executing here
2020-04-26 19:03:24.613 Status: dzVents: !Info: although you will see an error. The script is still executing here
2020-04-26 19:03:24.613 Status: dzVents: !Info: although you will see an error. The script is still executing here
2020-04-26 19:03:24.613 Status: dzVents: !Info: although you will see an error. The script is still executing here
2020-04-26 19:03:24.613 Status: dzVents: !Info: although you will see an error. The script is still executing here
2020-04-26 19:03:24.613 Status: dzVents: !Info: although you will see an error. The script is still executing here
2020-04-26 19:03:24.613 Status: dzVents: !Info: ítem is: {["type"]="customEvent", ["isSystem"]=false, ["isDevice"]=false, ["status"]="info", ["isTimer"]=false, ["data"]={"Up", {}}, ["isHardware"]=false, ["isHTTPResponse"]=false, ["isCustomEvent"]=true, ["isSecurity"]=false, ["trigger"]="faultyJSON", ["isGroup"]=false, ["isVariable"]=false, ["message"]="", ["isScene"]=false}
2020-04-26 19:03:24.613 Status: dzVents: !Info: item.data: {"Up", {}}
2020-04-26 19:03:24.613 Status: dzVents: Info: ------ Finished dz JSON reader

[Hesitated]

Yes you can get an Error message but the script will continue (at least it does on my systems (dzVents 3.0.2)

Just updated to 20202.2, to be sure...

I'll feel sighted blind, but eventually solved the mistery:

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    local lodash = dz.utils._
    local json = dz.utils.fromJSON(item.data)
    if json == nil then
      dz.log('item.data is not json: ' .. lodash.str(item.data), dz.LOG_FORCE)
      return
    end

is now looging:

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2020-04-26 22:04:50.204 Status: dzVents: Info: Bediening rolluiken: ------ Start internal script: BedieningRolluiken: Custom event: "BedieningRolluiken"
2020-04-26 22:04:50.204 Status: dzVents: !Info: Bediening rolluiken: item.data is not json: {"Up", {}}
2020-04-26 22:04:50.204 Status: dzVents: Info: Bediening rolluiken: ------ Finished BedieningRolluiken
2020-04-26 22:04:50.204 Error: dzVents: Error: (3.0.2) Bediening rolluiken: Error parsing json to LUA table: /home/pi/domoticz/scripts/dzVents/../lua/JSON.lua:808: expected string argument to JSON:decode(), got table 

I'm probably confused by the fact that the error message is shown after the last line of the script.

The function dz.utils._.str() is very usefull, thanxs!