Sample: Web access from a plug-in

项目
04/10/2023

This sample shows how to write a plug-in that can access web (network) resources like a web service or feed. It also demonstrates how to limit the time duration allowed for this call.

SDK for .NET: Web access from a plug-in sample code

How to run this sample

Download or clone the Samples repo so that you have a local copy. This sample is located under PowerApps-Samples-master\dataverse\orgsvc\C#\WebAccessPlugin.
There are two different plug-in class examples:
- WebClientPlugin uses WebClient Class
- HttpClientPlugin uses HttpClient Class
Open the sample solution in Visual Studio, navigate to the project's properties, and verify the assembly will be signed during the build. Press F6 to build the sample's assembly (WebAccessPlugin.dll).
Run the Plug-in Registration tool and register the assembly in the Microsoft Dataverse server's sandbox and database.
For either plug-in type, when registering a step, specify a web URI string (i.e., https://www.microsoft.com) in the unsecure configuration column.
- The default value https://www.bing.com will be used if none is provided.
Using an app or write code to perform the appropriate operation to invoke the message and table request that you registered the plug-in on.
When the plug-in runs, if the duration of the call exceeds the 15 second limit, it will throw an error. Otherwise it should succeed.
When you are done testing, unregister the assembly and step.

What this sample does

When executed, the plug-in downloads web page data from the specified web service address (or the default address). If the request exceeds the 15 second limit it will throw an InvalidPluginExecutionException and write details to the Plug-in Trace Log.

If the WebClientPlugin plugin fails, it will write something like the following to the Plug-in Trace log:

Downloading the target URI: https://www.bing.com
Exception: Microsoft.Xrm.Sdk.InvalidPluginExecutionException: The timeout elapsed while attempting to issue the request. ---> System.Net.WebException: The operation has timed out
  at System.Net.WebClient.DownloadDataInternal(Uri address, WebRequest& request)
  at System.Net.WebClient.DownloadData(Uri address)
  at PowerApps.Samples.WebClientPlugin.Execute(IServiceProvider serviceProvider)
  --- End of inner exception stack trace ---
  at PowerApps.Samples.WebClientPlugin.Execute(IServiceProvider serviceProvider)

If the HttpClientPlugin plug-in fails, it will write something like the following to the Plug-in Trace log:

Downloading the target URI: https://www.bing.com
Inner Exceptions:
  Exception: System.Threading.Tasks.TaskCanceledException: A task was canceled.
Exception: Microsoft.Xrm.Sdk.InvalidPluginExecutionException: An exception occurred while attempting to issue the request.
   at PowerApps.Samples.HttpClientPlugin.Execute(IServiceProvider serviceProvider)

The TaskCanceledException is somewhat ambigous about the cause of the task being cancelled. For a more complete solution showing how to explicitly detect errors due to time outs, see this blog post: Better timeout handling with HttpClient.

How this sample works

In order to simulate the scenario described in What this sample does, the sample will do the following:

Setup

Checks the constructor's unsecure configuration parameter for a web address value; otherwise, the default value is used.
Depending on which plug-in is registered, either the WebClient Class or HttpClient Class class is used by the plug-in's Execute method to download web page data.
If the call exceeds the 15 second duration specified, an InvalidPluginExecutionException will be thrown and details about the error will be written to the Plug-in Trace Log.

Demonstrate

WebClientPlugin plugin

Uses a derived CustomWebClient class to set the WebRequest.Timeout Property that is not available in the WebClient class.

 /// <summary>
 /// A class derived from WebClient with 15 second timeout and KeepAlive disabled
 /// </summary>
 public class CustomWebClient : WebClient
 {
   protected override WebRequest GetWebRequest(Uri address)
   {
     HttpWebRequest request = (HttpWebRequest)base.GetWebRequest(address);
     if (request != null)
     {
       request.Timeout = 15000; //15 Seconds
       request.KeepAlive = false;

     }
     return request;
   }
 }

Uses the WebClient.DownloadData Method to download the data from the resource.
Shows how to parse the expected WebException Class and use the Status Property to determine whether the cause of the failure was due to a timeout.

HttpClientPlugin plugin

Uses the HttpClient Class and sets the Timeout Property to limit the allowed time for the operation to complete.
Catches the expected AggregateException Class and examines the inner exceptions for the expected TaskCanceledException

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