Monitoring Web Request Timing When Using SystemLink™ LabVIEW APIs

The SystemLink™ LabVIEW APIs issue http(s) web requests under the hood to communicate with SystemLink™.  You can enable web logging in a lower level VI that is part of the API.  This enables you to view all web requests made by the SystemLink™ LabVIEW APIs, including web request paths, execution timings and response status codes.  Note that you do need to have a full LabVIEW project for your LabVIEW code in order to perform the following steps.

Step 1: Enable the Logging Conditional Disable Symbol

1. In the LabVIEW Project Explorer, right-click your target (for example, My Computer) and select Properties
2. Navigate to the Conditional Disable Symbols page
3. Add a new symbol with the following parameters:
   • Name: ENABLE_SYSTEMLINK_LOGGING
   • Value: HTTP
4. Click OK to save and apply the changes

Step 2: Open and Run the Log HTTP Requests VI

1. Open the primary LabVIEW VI that uses your SystemLink™ APIs (this ensures that its dependencies are loaded into the project)
2. In the Project Explorer, expand your target's Dependencies section
3. Navigate to vi.lib >> NI Skyline Utilities.lvlib >> HTTP
4. Open and run Log HTTP Requests.vi

Step 3: Monitor the Web Request Traffic

1. Keep the Log HTTP Requests.vi running in the background.
2. Execute your application or run the specific SystemLink™ VIs you want to monitor.
3. The generated http(s) requests will appear dynamically on the front panel of Log HTTP Requests.vi, allowing you to monitor web request paths, execution timings and response status codes.

⚠️ Important Note

Once you are done troubleshooting or monitoring your traffic, remember to remove the ENABLE_SYSTEMLINK_LOGGING conditional disable symbol from your target properties. Leaving this symbol enabled introduces additional logging overhead for all SystemLink™ http(s) requests, which can affect application performance [1].

You have a background VI running that will protocol any web requests the SystemLink LabVIEW APIs make:
 

1. Open the Query and Download Files.lvproj from LabVIEW's NI Example Finder
   
    
2. Right-click My Computer in the project tree and select Properties.
    
   
   
3. Select Conditional Disable Symbols, then add a new entry with name ENABLE_SYSTEMLINK_LOGGING and value HTTP
    
   
   
4. Now that the new Conditional Disable Symbol has been added, click OK to accept the change and exit the dialog
    
   
   
5. Open the Host.vi, which you will run later, and which will also ensure the Log HTTP Request.vi appears in the project tree
    
   
   
6. Expand your target's Dependencies list, then navigate to vi.lib >> NI Skyline Utilities.lvlib >> HTTP
    
   
   
7. Open the Log HTTP Requests.vi and run it.  Now this VI will show any subsequent http(s) calls from LabVIEW to SystemLink™
    
8. Now run the Host.vi you opened earlier and click one of the offered files to download it
    
9. Finally view the Log HTTP Requests.vi you left running in the background, which shows the web requests LabVIEW made to SystemLink™,  including web request paths, execution timings and response status codes
   

Next Steps

You can take this approach with any VI you create that uses the SystemLink™ LabVIEW APIs, and which resides in a LabVIEW project.  You can use the Log HTTP Requests.vi, running in the background, to debug or optimize the parts of your LabVIEW code that call the SystemLink™ LabVIEW APIs.