Transform synchronous function into asynchronous

Question

I would like to know how I can change the function below to the async method

my code:

Public Function GetPostWebService(urlget As String, stringdata As String) As String
Dim result As String = ""
Dim url As String
If internet_on_line = True Then

    Try
        Dim milliseconds = CLng(DateTime.UtcNow.Subtract(New DateTime(1970, 1, 1)).TotalMilliseconds)
        Dim uncache = milliseconds.ToString

        url = "https://" & apiUrl & "/webservice/" & urlget & "&data=" & stringdata & "&uncache=" & uncache

        Console.WriteLine("URL: " & url)
        Dim fr As System.Net.HttpWebRequest
        Dim targetURI As New Uri(url)
        ServicePointManager.Expect100Continue = True
        ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12
        fr = DirectCast(WebRequest.Create(targetURI), System.Net.HttpWebRequest)
        fr.UserAgent = "Mozilla/4.0 (compatible)"
        fr.Timeout = 15000
        Dim str As New System.IO.StreamReader(fr.GetResponse().GetResponseStream())
        result = str.ReadToEnd()
        str.Dispose()
        str.Close()

        Return result
    Catch ex As Exception
        result = "[ERROR]"
        Return result
        Dim func_name = New StackTrace(ex).GetFrame(0).GetMethod().Name
        If func_name = "GetResponse" Then
            writeExeption(ex, False)
        Else
            writeExeption(ex, True)
        End If
        Console.WriteLine("GetPostWebService Falhou: " & ex.Message & " - " & result)
    End Try
Else
    result = "[ERROR]"
    Return result
End If
End Function

I tried to use the suggestion given in this link: Implementing HttpWebRequest Async calls, but I was unable to implement it.

Any suggestions on how I can transform this function into asynchronous mode? The examples can be in both VB.net and C#

You have a StreamReader.ReadToEndAsync - method, to use with the async/await pattern. The linked question is old, and predates the modern asynchronous patterns. — JonasH
– JonasH, Commented Feb 29, 2024 at 15:56
HttpWebRequest is deprecated. Get rid of all of this and use HttpClient instead. Only use Await not .Result or .Wait. Make sure you dispose with a Using. Don't mess with ServicePointManager. — Charlieface
– Charlieface, Commented Feb 29, 2024 at 16:03
@Charlieface Thank you very much for the answer, I took a look at the new documentation of HttpClient and summarized the code as follows: Using response As HttpResponseMessage = Await client.GetAsync(url) response.EnsureSuccessStatusCode() result = Await response.Content.ReadAsStringAsync() End Using The question that's bothering me now is in relation to the useragent, which I haven't yet identified how to send. — Luiz
– Luiz, Commented Feb 29, 2024 at 17:47
Instead of using GetAsync, you need to create a HttpRequestMessage where you can headers. then pass it to SendAsync. — Charlieface
– Charlieface, Commented Feb 29, 2024 at 21:03

Luiz · Accepted Answer · 2024-02-29 19:42:49Z

With the help of @Charlieface and also from @JonasH, I managed to put together the code below and it is working perfectly.

Public Function GetPostWebService(urlget As String, stringdata As String) As String
 Dim url As String
 Dim result As String = ""
 Try
 Dim milliseconds = CLng(DateTime.UtcNow.Subtract(New DateTime(1970, 1, 1)).TotalMilliseconds)
 Dim uncache = milliseconds.ToString

 url = "https://" & apiUrl & "/webservice/" & urlget & "?token=" & data.app_config_token & "&data=" & stringdata & "&uncache=" & uncache

 Using client As HttpClient = New HttpClient()
     client.DefaultRequestHeaders.Clear()
     client.DefaultRequestHeaders.UserAgent.ParseAdd("Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)")
     Using response As HttpResponseMessage = Await client.GetAsync(url)
         response.EnsureSuccessStatusCode()
         result = Await response.Content.ReadAsStringAsync()
         Console.WriteLine(result)
         Return result
     End Using
 End Using

Catch ex As HttpRequestException
 Console.WriteLine(vbLf & "Exception Caught!")
 Console.WriteLine("Message :{0} ", ex.Message)
 result = "[ERROR]"
 Return result
 writeExeption(ex, True)
Catch ex As Exception
 result = "[ERROR]"
 Return result
 Dim func_name = New StackTrace(ex).GetFrame(0).GetMethod().Name
 If func_name = "GetResponse" Then
     writeExeption(ex, False)
 Else
     writeExeption(ex, True)
 End If
 Console.WriteLine("GetPostWebService Falhou: " & ex.Message & " - " & result)
End Try
End Function

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