Web Services in LabVIEW

What LabVIEW web services can do for you: An in depth guide to building web services into your applications and deploying them to your target machines.

Design test automation systems in LabVIEW for last 16 years. Medical Telecomm Software (using COM interfaces, XML) Network Servers (multiple simultaneous asyncronous

DUTs from single TE) Using LabVIEW since 1993 (version 3.1). EE from MTU. Know some C, C++, C#,

JavaScript but prefer LabVIEW. Believe there is nothing you can’t do in LabVIEW

(if you try hard enough!)

Wikipedia: “a software system designed to

support interoperable machine-to-machine interaction over a network.” (http://en.wikipedia.org/wiki/Web_service)

National Instruments: “more open and standard way to communicate with VIs

over the Web.”

My Definition: An API that allows (nearly) any language or tool to

interface with your application.

NI.com Links

Web Services in LabVIEW

▪ http://zone.ni.com/devzone/cda/tut/p/id/7350

LabVIEW Web Services FAQ

▪ http://zone.ni.com/devzone/cda/tut/p/id/7747

LabVIEW Web Services Security

▪ http://zone.ni.com/devzone/cda/tut/p/id/7749

Web Service Build Specification Builds lvws file

RESTful Web Server Must be enabled when testing in IDE

Must be disabled to build for distribution Sending Parameters Must include httpRequestID if returning stream data

Pitfalls▪ Cannot send case sensitive data (converts everything to lower case)

▪ Cannot send file paths (must use substitute for /, I like to use ~)

▪ Cannot send file names at end of call (browser will think it points to a file)

Returning Data

XML Format

Text Format

HTML Format

Streaming MIME data

Application Instances you must understand:▪ The Web Service Instance

▪ This is the app instance of the LabVIEW exe that has the web service enabled in its ini file. The NI Web Server Service is on port 3364.

▪ The IDE Instance▪ Always on port 3363 (unless you changed it). Will block any other app

on same port.

▪ Your EXE Instance▪ Recommend using a unique port number.

Connecting to the right instance▪ Must Use IP (demo of how to get this programmatically)

▪ Must have VI Server Enabled and set to unique port. (Must set this in the EXE ini file)

Cannot use normal methods (queues, notifiers)

Calling interface VI with VI Server

VI must be in memory (how to accomplish this)

▪ See EXAMPLE - EXE with screenshot enabled.vi

VI can push data into a queue.

How to use queues to wait for a response (demo)

Calling a web service from LabVIEW

Converting the XML into an Array of Clusters

▪ (see call web service.vi for demo)

Calling your web service from HTML

Demo of F5 test system web interface

You can use any web enabled script or language to call your web service (makes your application ‘scriptable’)

Building a web service into an application

Build Specification (the order in the project is important!)

▪ Turn off the Web Server before you build

Custom Files you must include

▪ niwebserver.conf (how to create and edit, MIME issue)

▪ The www folder (and how to make it appear)

Setting up the Installer

Passing in data (discussed above) Niwebserver.conf file tweaks The build process is a PITA (and very non-intuitive).

Seems like distribution was an afterthought. Hope for the future?

Double Installation issue Log folder missing

C:\Program Files\National Instruments\Shared\LabVIEW Run-Time\8.6\webserver\logs

Hard to debug! Must build with diagrams included (Source File Settings) and

breakpoints already set. Distributed System Manager

▪ Refresh does not work▪ URL path display sometimes works, sometimes not

Where to get it:▪ http://lavag.org/index.php?app=downloads&showfile=80

What does it do? Runs as a Windows service (project docs explain

how this is done)

Keeps the RESTful web server up and running. (see ini file)

Deploys new web services you install automatically

Provides some cool utilities!

Test the web server

Echo

Get a screenshot

Remote screen must be rendered (active user)

Get the front panel image of any VI

VI must be in memory

Get the version of any EXE

EXE must be running

Demo using iPod

Create a Universal API Can access any LabVIEW application

anywhere in the world Multiple access methods Not simple (yet) to use, but should get better Hard to debug! Only limited by your imagination…