Parsing Xml Return From Http.get Call

[SteveMyres]

The HTTP.Get() example in the manual shows to put the return in a string, specifically:

global string datain
datain = HTTP.Get("www.weather.gov", "/xml/current_obs/KWMC.xml")[/CODE]

I make an HTTP.Get call to a web service that returns the following:

<boolean xmlns="http://schemas.microsoft.com/2003/10/Serialization/">true</boolean>

and assigns it to the variable. You can echo the variable to the command line with ?datain, but string functions such as find() fail. What are the proper steps to parse this type of return?

[AzeoTech]

String functions should work fine. What do you mean by "fail"? What are you trying?

[SteveMyres]

Well, I was trying to do a find() to check the true/false return value, but it wouldn't seem to work yesterday. I was doing it from the command line and I probably got the syntax wrong. Seems to work find today. Sorry about the false alarm!

[ledbelly2142]

In my experience, www.weather.gov is not 100% consistent. So you may have had it correct in the command line and the www.weather.gov/... server was not responding correctly.

[SteveMyres]

I wasn't actually Get()ing from weather.gov. That's just a quote from the manual to demonstrate usage.

[SteveMyres]

This HTTP.Get() call takes like 6-8 seconds to return, and in the meantime my Modbus comms (on the same ethernet port) report "Illegal data address" which I suspect may be the error shown for no response because the port is tied up. Is there a way to be able to use the port for both things simultaneously? Is a port thing or is it the sequence in which the Get() is called that's tying everything up?

[AzeoTech]

They shouldn't be linked together at all. Is it repeatable?

[SteveMyres]

More often than not. Here's the sequence:

global string FileSelected = Registry.strFileSelected
private idx

while(1)
   try()
   if((MarkFileSelected > -1) & (MarkFileList[MarkFileSelected] != FileSelected) & !SysBits[0][0] & (N7024[0] < 5))
	  FileSelected = MarkFileList[MarkFileSelected]
	  switch
		 case (FileSelected == "xPOINT05MG")
		    idx = 1
		 case (FileSelected == "xPOINT1MGx")
		    idx = 2
		 case (FileSelected == "xPOINT2MGx")
		    idx = 3
		 endcase
	  ?"Idx: " + idx
	  Device.PLC.SetRegisterS16(PLC_Stn, 112, idx)
	  private string ParseRet = MakeUpper(ParseXML(HTTP.Get("localhost", "/LoadFile/" + FileSelected + ".dat")))
	  if(ParseRet == "TRUE")
		 ?"File Accepted"
		 Registry.strFileSelected = FileSelected
	  else
		 ?"File Not Accepted"
		 endif		   
	  endif
   catch()
	  ?"Error"
   endcatch
   delay(0.2)
   endwhile[/CODE]

And from the Command/Alert Window:

Idx: 3

File Accepted

11/05/12 12:46:32.706

P-ModbusTCP 0003: Illegal Data Value

markfileselected = 1

Idx: 1

File Accepted

11/05/12 12:46:58.619

P-ModbusTCP 0003: Illegal Data Value

Or do you think the 0003 error is coming from the Device call in the sequence?

[AzeoTech]

Illegal data value is an error generated by the device. It isn't a communications issue, its simply that you are asking it to set a value that isn't correct. Are you sure that your setRegisterS16() parameters are correct? I'll bet if you look at the comm monitor for when it does that command, that DAQFactory is successfully outputting the correct Modbus command and you are getting a valid (albeit error) response from the device.

[SteveMyres]

Can't imagine why it would be a problem. It's just the 113th integer register in a block of a couple hundred. No particular limits on what can be written there. Any 16 bits should work, and certainly integer values of 1-3. It's the same call as numerous other places. Even so, I'll experiment and see if I can figure out what it doesn't like.

[SteveMyres]

From the Command/Alert window:

?device.plc.SetRegisterS16(PLC_Stn, 112, 1)

?device.plc.ReadHoldingS16(PLC_Stn, 112, 1)

1

?device.plc.SetRegisterS16(PLC_Stn, 112, 2)

?device.plc.ReadHoldingS16(PLC_Stn, 112, 1)

2

?device.plc.SetRegisterS16(PLC_Stn, 112, 3)

?device.plc.ReadHoldingS16(PLC_Stn, 112, 1)

3

So the slave doesn't seem to object to any of the relevant values being written to that address if it's done manually from the prompt. What would be the difference?

[AzeoTech]

Try removing the HTTP.get() function and replacing it with something static and see if it fixes the problem.

[SteveMyres]

Oh, and please don't laugh about the filenames hardcoded into the sequence. It's just a quick band-aid to temporarily restore compatibility with something that was inflicted on me in another part of the system. As soon as I get five minutes I'll do a GUI for mapping the filenames to the ordinals.

[AzeoTech]

I wasn't laughing. I was giving you a valid suggestion. If you think HTTP.Get() is causing the problem, remove it and see if it fixes the problem.

[SteveMyres]

No, no, that wasn't in response to what you said, it was just my own embarrassment about the hardcoded list of file names in the sequence.

I have played with the sequence some without definitive results yet. Will post when I have some.

[AzeoTech]

Sorry, please remember that I read these things totally out of order across multiple posts / emails, so often don't follow the full train of thought of the thread, especially with longer threads.