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Developing HTTP Method VIs (Real-Time, Windows)

LabVIEW 2013 Help

Edition Date: June 2013

Part Number: 371361K-01

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Parent Topic: Components of a Web Service

Note  For more information about concepts in this topic, refer to the Web services introduction and tutorial. LabVIEW Web services are available only in the LabVIEW Full Development System and the LabVIEW Professional Development System.

To create an HTTP method VI, right-click Web Resources or a web resource sub-item in the Project Explorer window and select New VI. LabVIEW opens the new VI, which contains a LabVIEW Web Service Request control you commonly use in HTTP method VIs.

Consider the guidelines in the following sections for developing HTTP method VIs.

Transferring Data between HTTP Method VIs and Web Clients

HTTP method VIs receive and send data using their connector pane terminals. When a web client sends an HTTP request to an HTTP method VI, the VI receives values for controls on its connector pane, processes those values, and returns a response to the client.

The following figure displays an example front panel, block diagram, and connector pane for an HTTP method VI that accepts two values from a web client and returns their sum.

Block Diagram Front Panel Connector Pane

Labels of controls and indicators that receive and return values in Web services can contain only letters, numbers, hyphens, and underscores available in the US ASCII character set. Labels cannot contain spaces or special characters.

Related Information

Sending Data to a Published Application using URLs

Assigning Terminals to Controls and Indicators

Choosing the Format of Output Data

By default, an HTTP method VI returns data to web clients as an XML string. The XML string includes a summary of the indicator values assigned to the connector pane of the HTTP method VI. You also can configure an HTTP method VI to return data as an HTML-, plain text-, or JSON-formatted response. Configure the output format type on the HTTP Method VI Settings page of the Web Service Properties dialog box.

Note  Instead of returning data to a client via the connector pane, an HTTP method VI can stream data to a client in a custom format, such as a customized HTML page or image data.

Related Information

Configuring HTTP Headers, Streaming, and Buffering

Using the VIs on the Web Services Palette

The VIs on the Web Services palette can handle post data, form data, HTTP sessions, cookies, and other Web-specific functionality. When you include VIs from the Web Services palette within an HTTP method VI, you must wire the LabVIEW Web Service Request input on each VI so they uniformly handle the current HTTP request. The LabVIEW Web Service Request input functions similarly to a refnum in LabVIEW.

The following figure shows the use of the LabVIEW Web Service Request input to identify the HTTP request for which the Read Request Variable VI returns data:

Note  You must assign the control wired to LabVIEW Web Service Request to the connector pane of the top-level HTTP method VI.

If an HTTP method VI contains multiple VIs from the Web Services palette, you can wire a single control to the LabVIEW Web Service Request input on the first Web Services VI, and then wire the subsequent VIs together using the LabVIEW Web Service Request input and LabVIEW Web Service Request out output of each VI.

Refer to the examples\Connectivity\Web Services\Address Book\Web Services - Address Book.lvproj for examples of HTTP method VIs in a Web service.

Using Other Built-in LabVIEW Nodes

HTTP method VIs can include nearly all of the available functionality of LabVIEW that uses supported data types.

Related Information


 

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