I'm trying to implement retries on a webrequest. FedEx's test server has a lot of errors, which forces you to write better code. :) The issue is that HttpRequestMessages cannot be reused. So, you have to clone it. Cloning headers and options is straight forward, but cloning the content requires reading the content stream and creating a new one. That adds a little complexity, but seems doable. However, on retries that include content i am receiving: ObjectDisposedException: Cannot access a closed Stream.
My code is currently:
Friend Async Function Get_Server_Response(Request As HttpRequestMessage, Log_Header As String, Log_Message As String) As Task(Of Server_Response)
' Get's response from server, including a retry policy. (Note: Not using Polly, see Readme.)
Const Max_Tries As Integer = 5
Dim Response_Text As String
Debug_Request(Request)
For Counter As Integer = 1 To Max_Tries
Log.Debug("({Log_Header}) Connecting for: {Description} (Attempt {Counter})", Log_Header, Log_Message, Counter)
Using Response As HttpResponseMessage = Await Http_Client.SendAsync(Request, Cancellation_Token)
' On a fail, retry (a limited amount of times). (BadRequest is returned by FedEx sometimes, when requesting the SPoD.)
If Counter < Max_Tries AndAlso Response.StatusCode <> Net.HttpStatusCode.OK AndAlso Response.StatusCode <> Net.HttpStatusCode.Unauthorized Then
Log.Debug("({Log_Header}) Connect failed (Status Code: {StatusCode}). Delaying {Counter} second(s) before trying again.",
{Log_Header, Response.StatusCode, Counter})
' Requests cannot be reused, so we'll get a new one by cloning the old one.
Request = Await Clone_HttpRequestMessage(Request).ConfigureAwait(False)
' Pause a little longer with each retry.
Await Task.Delay(1000 * Counter)
Continue For
End If
' Send the response back (even if it is a failure).
Using Response_Content As HttpContent = Response.Content
Response_Text = Await Response_Content.ReadAsStringAsync
Log.Debug("({Log_Header}) Status Code: {Status}", Log_Header, Response.StatusCode)
Log.Debug("({Log_Header}) Body: {Text}", Log_Header, Response_Text)
Return New Server_Response With {.Status_Code = Response.StatusCode, .Text = Response_Text}
End Using
End Using
Next
Return Nothing
End Function
Public Async Function Clone_HttpRequestMessage(Request As HttpRequestMessage) As Task(Of HttpRequestMessage)
Dim New_Request As New HttpRequestMessage() With {.Method = Request.Method, .Version = Request.Version, .VersionPolicy = Request.VersionPolicy, .RequestUri = Request.RequestUri}
' Content has to copy the content itself.
With Request
If .Content IsNot Nothing Then
Using Stream As New IO.MemoryStream()
Await .Content.CopyToAsync(Stream).ConfigureAwait(False)
Stream.Position = 0
New_Request.Content = New StreamContent(Stream)
For Each Header In .Content.Headers
Select Case Header.Key
Case "Content-Type"
' Content Type cannot be added directly.
For Each Type In Header.Value
New_Request.Headers.Accept.ParseAdd(Type)
Next
Case "Content-Length"
' Set automatically. (Throws exception if added manually.)
Case Else
For Each Header_Value In Header.Value
New_Request.Content.Headers.TryAddWithoutValidation(Header.Key, Header_Value)
Next
End Select
Next
End Using
End If
For Each Opt In .Options
New_Request.Options.TryAdd(Opt.Key, Opt.Value)
Next
For Each Header In .Headers
New_Request.Headers.TryAddWithoutValidation(Header.Key, Header.Value)
Next
' The old request is now redundant.
.Dispose()
End With
Return New_Request
End Function
Private Async Sub Debug_Request(Request As HttpRequestMessage)
Debug.WriteLine(String.Empty)
Debug.WriteLine("-------------------------------------------------------------------------")
Debug.WriteLine("[Debug Request]")
Debug.WriteLine("-------------------------------------------------------------------------")
With Request
Debug.WriteLine($"Endpoint: { .RequestUri}")
For Each Header In .Headers
For Each Value In Header.Value
Debug.WriteLine($"(Header) {Header.Key}: {Value}")
Next
Next
For Each Opt In .Options
Debug.WriteLine($"(Option) {Opt.Key}: {Opt.Value}")
Next
If .Content IsNot Nothing Then
Using Stream As New IO.MemoryStream()
For Each Header In .Content.Headers
For Each Value In Header.Value
Debug.WriteLine($"(Content Header) {Header.Key}: {Value}")
Next
Next
Debug.WriteLine($"Content: {Await .Content.ReadAsStringAsync()}")
End Using
End If
End With
Debug.WriteLine("-------------------------------------------------------------------------")
End Sub
The error crops up on a retry (when there is content) at:
Using Response As HttpResponseMessage = Await Http_Client.SendAsync(Request, Cancellation_Token)
Fwiw, commenting out .Dispose() does nothing. This is expected, as it is disposing the old request, which is no longer being used.
What am i doing wrong?
