ControllingTheInter.net

In .NET core, Microsoft recently released DevTunnels which creates an outgoing connection to a centralized service which receives request from an external provided URL when subscribing to the service, sadly there is no equivalent solution for .NET Framework. As a quick fix I threw together a proxy that resolves this issue exposing the self-hosted debug session externally to any address you prefer. Assuming you code in user (non-admin) mode which is recommended, you may have to add the ACL to netsh to allow hosting at a particular IP/HOSTNAME.

The result of this post is that port 8080 will be forwarded to port 4858. Set port 4858 to the default port used by your IIS Debug session within visual studio.

Public Shared Async Sub LoadDebugProxy(args As String())
    Dim IpAddressString As String
    Dim listenPortNum As Integer
    Dim forwardPortNum As Integer

    If args.Length < 3 OrElse Not Integer.TryParse(args(1), listenPortNum) OrElse Not Integer.TryParse(args(2), forwardPortNum) Then
        Debug.WriteLine("Usage: SimpleHttpProxy.exe <listenIP> <listenPort> <forwardPort>")
        Debug.WriteLine("Example: SimpleHttpProxy.exe 8080 5000")
        Return
    End If

    Dim server As New SimpleProxy(listenPortNum, forwardPortNum)
    Try
        IpAddressString = args(0)
        Debug.WriteLine($"Starting proxy server {listenPortNum}->{forwardPortNum}...")
        server.Start(IpAddressString).GetAwaiter().GetResult() ' Synchronously wait for Start to complete (which it won't, as it's an infinite loop)
    Catch ex As Exception
        Debug.WriteLine($"Proxy server failed to start or crashed: {ex.ToString()}")
    End Try
    Debug.WriteLine("Proxy server stopped.")
End Sub

Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
    If Debugger.IsAttached() Then
        Dim MyLoadDebugProxyThread As New Threading.Thread(AddressOf LoadDebugProxy) 'This requires FULL site access due to TCP port!
        MyLoadDebugProxyThread.Start({"MyDNSNAme.noip.com", "8080", "4858"})
    End If
end sub

Public Shared Async Sub LoadDebugProxy(args As String())

Dim IpAddressString As String

Dim listenPortNum As Integer

Dim forwardPortNum As Integer

If args.Length < 3 OrElse Not Integer.TryParse(args(1), listenPortNum) OrElse Not Integer.TryParse(args(2), forwardPortNum) Then

Debug.WriteLine("Usage: SimpleHttpProxy.exe <listenIP> <listenPort> <forwardPort>")

Debug.WriteLine("Example: SimpleHttpProxy.exe 8080 5000")

Return

End If

Dim server As New SimpleProxy(listenPortNum, forwardPortNum)

Try

IpAddressString = args(0)

Debug.WriteLine($"Starting proxy server {listenPortNum}->{forwardPortNum}...")

server.Start(IpAddressString).GetAwaiter().GetResult() ' Synchronously wait for Start to complete (which it won't, as it's an infinite loop)

Catch ex As Exception

Debug.WriteLine($"Proxy server failed to start or crashed: {ex.ToString()}")

End Try

Debug.WriteLine("Proxy server stopped.")

End Sub

Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)

If Debugger.IsAttached() Then

Dim MyLoadDebugProxyThread As New Threading.Thread(AddressOf LoadDebugProxy) 'This requires FULL site access due to TCP port!

MyLoadDebugProxyThread.Start({"MyDNSNAme.noip.com", "8080", "4858"})

End If

end sub

Imports System
Imports System.IO
Imports System.Linq
Imports System.Net
Imports System.Text
Imports System.Threading.Tasks

Public Class SimpleProxy
    Private ReadOnly _listenPort As Integer
    Private ReadOnly _forwardPort As Integer
    Private ReadOnly _forwardHost As String = "localhost"

    Public Sub New(listenPort As Integer, forwardPort As Integer)
        _listenPort = listenPort
        _forwardPort = forwardPort
    End Sub

    'This is required or will receive access denied
    'netsh http add urlacl url=http://{WANIP}:8080/ user=EVERYONE 'WanIP
    'netsh http add urlacl url=http://192.168.0.XX:8080/ user=EVERYONE 'LANIP, 
    'netsh http add urlacl url=http://+:8080/ user=EVERYONE 'All IP's <-- requires admin during runtime
    'netsh http add urlacl url=http://MyHostName.com:8080/ user=EVERYONE <-- DNS name
    Public Async Function Start(HostnameOrIP As String) As Task
        Dim listener As New HttpListener()
        Dim AddressToListenOn As String = $"http://{HostnameOrIP}:{_listenPort}/"
        listener.Prefixes.Add(AddressToListenOn)
        listener.Start()
        Debug.WriteLine($"Proxy listening on {AddressToListenOn}, forwarding to {_forwardHost}:{_forwardPort}")

        Do While True
            Try
                Dim context As HttpListenerContext = Await listener.GetContextAsync()
                ProcessRequest(context) ' Fire and forget Async Sub
            Catch ex As HttpListenerException
                If ex.ErrorCode = 995 Then Return ' Listener closed (occurs during shutdown)
                Debug.WriteLine($"Listener Error: {ex.Message}")
            Catch ex As Exception
                Debug.WriteLine($"Error accepting request: {ex.Message}")
            End Try
        Loop
    End Function

    Private Async Sub ProcessRequest(context As HttpListenerContext)
        Dim incomingRequest As HttpListenerRequest = context.Request
        Dim proxyResponse As HttpListenerResponse = context.Response
        Dim targetUrl As String = $"http://{_forwardHost}:{_forwardPort}{incomingRequest.RawUrl}"

        Dim forwardRequest As HttpWebRequest = DirectCast(WebRequest.Create(targetUrl), HttpWebRequest)

        Try
            forwardRequest.Method = incomingRequest.HttpMethod
            forwardRequest.ProtocolVersion = incomingRequest.ProtocolVersion
            forwardRequest.UserAgent = incomingRequest.UserAgent
            If incomingRequest.UrlReferrer IsNot Nothing Then
                forwardRequest.Referer = incomingRequest.UrlReferrer.AbsoluteUri
            End If
            forwardRequest.KeepAlive = incomingRequest.KeepAlive
            forwardRequest.ServicePoint.Expect100Continue = False

            For Each headerKey As String In incomingRequest.Headers.AllKeys
                Dim value As String = incomingRequest.Headers(headerKey)
                Try
                    Select Case headerKey.ToLowerInvariant()
                        Case "host"
                            forwardRequest.Host = $"{_forwardHost}:{_forwardPort}"
                        Case "connection"
                            If value.ToLowerInvariant().Contains("keep-alive") Then
                                forwardRequest.KeepAlive = True
                            ElseIf value.ToLowerInvariant().Contains("close") Then
                                forwardRequest.KeepAlive = False
                            Else
                                forwardRequest.Connection = value
                            End If
                        Case "content-length"
                            forwardRequest.ContentLength = incomingRequest.ContentLength64
                        Case "content-type"
                            forwardRequest.ContentType = incomingRequest.ContentType
                        Case "accept"
                            forwardRequest.Accept = value
                        Case "expect"
                            If String.Equals(value, "100-continue", StringComparison.OrdinalIgnoreCase) Then
                                Continue For
                            End If
                            forwardRequest.Headers.Add(headerKey, value)
                        Case "if-modified-since"
                            Dim dt As DateTime
                            If DateTime.TryParse(value, dt) Then
                                forwardRequest.IfModifiedSince = dt
                            End If
                        Case "user-agent", "referer", "proxy-connection"
                            ' User-Agent and Referer already set or handled by specific properties, Proxy-Connection is hop-by-hop
                        Case Else
                            forwardRequest.Headers.Add(headerKey, value) 'Range=bytes=0-
                    End Select
                Catch ex As Exception
                    ' Skip restricted headers (e.g., if trying to set a protected header) or invalid values
                End Try
            Next

            If incomingRequest.HttpMethod <> "GET" AndAlso incomingRequest.HttpMethod <> "HEAD" AndAlso incomingRequest.ContentLength64 > 0 Then
                Using requestStream As Stream = Await forwardRequest.GetRequestStreamAsync()
                    Await incomingRequest.InputStream.CopyToAsync(requestStream)
                End Using
            ElseIf forwardRequest.Method = "POST" OrElse forwardRequest.Method = "PUT" Then
                If forwardRequest.ContentLength <= 0 AndAlso Not incomingRequest.Headers.AllKeys.Any(Function(k) k.Equals("Transfer-Encoding", StringComparison.OrdinalIgnoreCase)) Then
                    forwardRequest.ContentLength = 0
                End If
            End If

            Using targetResponse As HttpWebResponse = DirectCast(Await forwardRequest.GetResponseAsync(), HttpWebResponse)
                proxyResponse.StatusCode = CInt(targetResponse.StatusCode)
                proxyResponse.StatusDescription = targetResponse.StatusDescription
                proxyResponse.ProtocolVersion = targetResponse.ProtocolVersion

                Dim connHeaderValueTarget As String = targetResponse.Headers.Get("Connection")
                If connHeaderValueTarget IsNot Nothing Then
                    proxyResponse.KeepAlive = connHeaderValueTarget.ToLowerInvariant().Contains("keep-alive")
                Else
                    proxyResponse.KeepAlive = (targetResponse.ProtocolVersion >= HttpVersion.Version11)
                End If

                For i As Integer = 0 To targetResponse.Headers.Count - 1
                    Dim headerName As String = targetResponse.Headers.GetKey(i)
                    Dim headerValue As String = targetResponse.Headers.Get(i)

                    Select Case headerName.ToLowerInvariant()
                        Case "content-length"
                            proxyResponse.ContentLength64 = targetResponse.ContentLength
                        Case "content-type"
                            proxyResponse.ContentType = headerValue
                        Case "transfer-encoding", "connection", "keep-alive"
                            ' Transfer-Encoding is handled by CopyToAsync and HttpListener itself.
                            ' Connection and Keep-Alive headers from target are used to set proxyResponse.KeepAlive property.
                        Case Else
                            Try
                                proxyResponse.Headers.Add(headerName, headerValue)
                            Catch ex As Exception
                                ' Skip restricted headers
                            End Try
                    End Select
                Next

                Using responseStream As Stream = targetResponse.GetResponseStream()
                    If responseStream IsNot Nothing Then
                        Await responseStream.CopyToAsync(proxyResponse.OutputStream)
                    End If
                End Using
            End Using
        Catch webEx As WebException
            Try
                If webEx.Response IsNot Nothing AndAlso TypeOf webEx.Response Is HttpWebResponse Then
                    Dim errorResponse As HttpWebResponse = DirectCast(webEx.Response, HttpWebResponse)
                    proxyResponse.StatusCode = CInt(errorResponse.StatusCode)
                    proxyResponse.StatusDescription = errorResponse.StatusDescription
                    proxyResponse.ProtocolVersion = errorResponse.ProtocolVersion

                    For i As Integer = 0 To errorResponse.Headers.Count - 1
                        Dim headerName As String = errorResponse.Headers.GetKey(i)
                        Dim headerValue As String = errorResponse.Headers.Get(i)
                        Select Case headerName.ToLowerInvariant()
                            Case "content-length" : proxyResponse.ContentLength64 = errorResponse.ContentLength
                            Case "content-type" : proxyResponse.ContentType = headerValue
                            Case Else
                                Try : proxyResponse.Headers.Add(headerName, headerValue)
                                Catch : End Try ' Skip restricted
                        End Select
                    Next

                    If errorResponse.ContentLength > 0 Then
                        Using errorStream As Stream = errorResponse.GetResponseStream()
                            If errorStream IsNot Nothing Then
                                ' Using synchronous Write in Catch block
                                Dim buffer(4095) As Byte ' 4KB buffer
                                Dim bytesRead As Integer
                                Do
                                    bytesRead = errorStream.Read(buffer, 0, buffer.Length)
                                    If bytesRead > 0 Then
                                        proxyResponse.OutputStream.Write(buffer, 0, bytesRead)
                                    End If
                                Loop While bytesRead > 0
                            End If
                        End Using
                    End If
                    errorResponse.Close()
                Else
                    proxyResponse.StatusCode = 502 ' Bad Gateway
                    proxyResponse.StatusDescription = "Bad Gateway"
                    Dim body As Byte() = Encoding.UTF8.GetBytes($"Proxy error (WebException without HTTP response): {webEx.Message}")
                    proxyResponse.ContentType = "text/plain"
                    proxyResponse.ContentLength64 = body.Length
                    proxyResponse.OutputStream.Write(body, 0, body.Length) ' Synchronous Write
                End If
            Catch exInner As Exception
                ' If setting the error response itself fails (e.g., headers already sent)
                Debug.WriteLine($"Failed to send error response: {exInner.Message}")
            End Try
        Catch ex As Exception
            Try
                proxyResponse.StatusCode = 500 ' Internal Server Error
                proxyResponse.StatusDescription = "Internal Server Error"
                Dim body As Byte() = Encoding.UTF8.GetBytes($"Proxy error (General exception): {ex.Message}")
                proxyResponse.ContentType = "text/plain"
                proxyResponse.ContentLength64 = body.Length
                proxyResponse.OutputStream.Write(body, 0, body.Length) ' Synchronous Write
            Catch exInner As Exception
                Debug.WriteLine($"Failed to send 500 error response: {exInner.Message}")
            End Try
        Finally
            Try
                proxyResponse.Close()
            Catch finalEx As Exception
                Debug.WriteLine($"Error closing proxyResponse: {finalEx.Message}")
            End Try
        End Try
    End Sub
End Class

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Imports System

Imports System.IO

Imports System.Linq

Imports System.Net

Imports System.Text

Imports System.Threading.Tasks

Public Class SimpleProxy

Private ReadOnly _listenPort As Integer

Private ReadOnly _forwardPort As Integer

Private ReadOnly _forwardHost As String = "localhost"

Public Sub New(listenPort As Integer, forwardPort As Integer)

_listenPort = listenPort

_forwardPort = forwardPort

End Sub

'This is required or will receive access denied

'netsh http add urlacl url=http://{WANIP}:8080/ user=EVERYONE 'WanIP

'netsh http add urlacl url=http://192.168.0.XX:8080/ user=EVERYONE 'LANIP,

'netsh http add urlacl url=http://+:8080/ user=EVERYONE 'All IP's <-- requires admin during runtime

'netsh http add urlacl url=http://MyHostName.com:8080/ user=EVERYONE <-- DNS name

Public Async Function Start(HostnameOrIP As String) As Task

Dim listener As New HttpListener()

Dim AddressToListenOn As String = $"http://{HostnameOrIP}:{_listenPort}/"

listener.Prefixes.Add(AddressToListenOn)

listener.Start()

Debug.WriteLine($"Proxy listening on {AddressToListenOn}, forwarding to {_forwardHost}:{_forwardPort}")

Do While True

Try

Dim context As HttpListenerContext = Await listener.GetContextAsync()

ProcessRequest(context) ' Fire and forget Async Sub

Catch ex As HttpListenerException

If ex.ErrorCode = 995 Then Return ' Listener closed (occurs during shutdown)

Debug.WriteLine($"Listener Error: {ex.Message}")

Catch ex As Exception

Debug.WriteLine($"Error accepting request: {ex.Message}")

End Try

Loop

End Function

Private Async Sub ProcessRequest(context As HttpListenerContext)

Dim incomingRequest As HttpListenerRequest = context.Request

Dim proxyResponse As HttpListenerResponse = context.Response

Dim targetUrl As String = $"http://{_forwardHost}:{_forwardPort}{incomingRequest.RawUrl}"

Dim forwardRequest As HttpWebRequest = DirectCast(WebRequest.Create(targetUrl), HttpWebRequest)

Try

forwardRequest.Method = incomingRequest.HttpMethod

forwardRequest.ProtocolVersion = incomingRequest.ProtocolVersion

forwardRequest.UserAgent = incomingRequest.UserAgent

If incomingRequest.UrlReferrer IsNot Nothing Then

forwardRequest.Referer = incomingRequest.UrlReferrer.AbsoluteUri

End If

forwardRequest.KeepAlive = incomingRequest.KeepAlive

forwardRequest.ServicePoint.Expect100Continue = False

For Each headerKey As String In incomingRequest.Headers.AllKeys

Dim value As String = incomingRequest.Headers(headerKey)

Try

Select Case headerKey.ToLowerInvariant()

Case "host"

forwardRequest.Host = $"{_forwardHost}:{_forwardPort}"

Case "connection"

If value.ToLowerInvariant().Contains("keep-alive") Then

forwardRequest.KeepAlive = True

ElseIf value.ToLowerInvariant().Contains("close") Then

forwardRequest.KeepAlive = False

Else

forwardRequest.Connection = value

End If

Case "content-length"

forwardRequest.ContentLength = incomingRequest.ContentLength64

Case "content-type"

forwardRequest.ContentType = incomingRequest.ContentType

Case "accept"

forwardRequest.Accept = value

Case "expect"

If String.Equals(value, "100-continue", StringComparison.OrdinalIgnoreCase) Then

Continue For

End If

forwardRequest.Headers.Add(headerKey, value)

Case "if-modified-since"

Dim dt As DateTime

If DateTime.TryParse(value, dt) Then

forwardRequest.IfModifiedSince = dt

End If

Case "user-agent", "referer", "proxy-connection"

' User-Agent and Referer already set or handled by specific properties, Proxy-Connection is hop-by-hop

Case Else

forwardRequest.Headers.Add(headerKey, value) 'Range=bytes=0-

End Select

Catch ex As Exception

' Skip restricted headers (e.g., if trying to set a protected header) or invalid values

End Try

If incomingRequest.HttpMethod <> "GET" AndAlso incomingRequest.HttpMethod <> "HEAD" AndAlso incomingRequest.ContentLength64 > 0 Then

Using requestStream As Stream = Await forwardRequest.GetRequestStreamAsync()

Await incomingRequest.InputStream.CopyToAsync(requestStream)

End Using

ElseIf forwardRequest.Method = "POST" OrElse forwardRequest.Method = "PUT" Then

If forwardRequest.ContentLength <= 0 AndAlso Not incomingRequest.Headers.AllKeys.Any(Function(k) k.Equals("Transfer-Encoding", StringComparison.OrdinalIgnoreCase)) Then

forwardRequest.ContentLength = 0

End If

Using targetResponse As HttpWebResponse = DirectCast(Await forwardRequest.GetResponseAsync(), HttpWebResponse)

proxyResponse.StatusCode = CInt(targetResponse.StatusCode)

proxyResponse.StatusDescription = targetResponse.StatusDescription

proxyResponse.ProtocolVersion = targetResponse.ProtocolVersion

Dim connHeaderValueTarget As String = targetResponse.Headers.Get("Connection")

If connHeaderValueTarget IsNot Nothing Then

proxyResponse.KeepAlive = connHeaderValueTarget.ToLowerInvariant().Contains("keep-alive")

Else

proxyResponse.KeepAlive = (targetResponse.ProtocolVersion >= HttpVersion.Version11)

End If

For i As Integer = 0 To targetResponse.Headers.Count - 1

Dim headerName As String = targetResponse.Headers.GetKey(i)

Dim headerValue As String = targetResponse.Headers.Get(i)

Select Case headerName.ToLowerInvariant()

Case "content-length"

proxyResponse.ContentLength64 = targetResponse.ContentLength

Case "content-type"

proxyResponse.ContentType = headerValue

Case "transfer-encoding", "connection", "keep-alive"

' Transfer-Encoding is handled by CopyToAsync and HttpListener itself.

' Connection and Keep-Alive headers from target are used to set proxyResponse.KeepAlive property.

Case Else

Try

proxyResponse.Headers.Add(headerName, headerValue)

Catch ex As Exception

' Skip restricted headers

End Try

End Select

Using responseStream As Stream = targetResponse.GetResponseStream()

If responseStream IsNot Nothing Then

Await responseStream.CopyToAsync(proxyResponse.OutputStream)

End If

End Using

Catch webEx As WebException

Try

If webEx.Response IsNot Nothing AndAlso TypeOf webEx.Response Is HttpWebResponse Then

Dim errorResponse As HttpWebResponse = DirectCast(webEx.Response, HttpWebResponse)

proxyResponse.StatusCode = CInt(errorResponse.StatusCode)

proxyResponse.StatusDescription = errorResponse.StatusDescription

proxyResponse.ProtocolVersion = errorResponse.ProtocolVersion

For i As Integer = 0 To errorResponse.Headers.Count - 1

Dim headerName As String = errorResponse.Headers.GetKey(i)

Dim headerValue As String = errorResponse.Headers.Get(i)

Select Case headerName.ToLowerInvariant()

Case "content-length" : proxyResponse.ContentLength64 = errorResponse.ContentLength

Case "content-type" : proxyResponse.ContentType = headerValue

Case Else

Try : proxyResponse.Headers.Add(headerName, headerValue)

Catch : End Try ' Skip restricted

End Select

If errorResponse.ContentLength > 0 Then

Using errorStream As Stream = errorResponse.GetResponseStream()

If errorStream IsNot Nothing Then

' Using synchronous Write in Catch block

Dim buffer(4095) As Byte ' 4KB buffer

Dim bytesRead As Integer

bytesRead = errorStream.Read(buffer, 0, buffer.Length)

If bytesRead > 0 Then

proxyResponse.OutputStream.Write(buffer, 0, bytesRead)

End If

Loop While bytesRead > 0

End If

End Using

End If

errorResponse.Close()

Else

proxyResponse.StatusCode = 502 ' Bad Gateway

proxyResponse.StatusDescription = "Bad Gateway"

Dim body As Byte() = Encoding.UTF8.GetBytes($"Proxy error (WebException without HTTP response): {webEx.Message}")

proxyResponse.ContentType = "text/plain"

proxyResponse.ContentLength64 = body.Length

proxyResponse.OutputStream.Write(body, 0, body.Length) ' Synchronous Write

End If

Catch exInner As Exception

' If setting the error response itself fails (e.g., headers already sent)

Debug.WriteLine($"Failed to send error response: {exInner.Message}")

End Try

Catch ex As Exception

Try

proxyResponse.StatusCode = 500 ' Internal Server Error

proxyResponse.StatusDescription = "Internal Server Error"

Dim body As Byte() = Encoding.UTF8.GetBytes($"Proxy error (General exception): {ex.Message}")

proxyResponse.ContentType = "text/plain"

proxyResponse.ContentLength64 = body.Length

proxyResponse.OutputStream.Write(body, 0, body.Length) ' Synchronous Write

Catch exInner As Exception

Debug.WriteLine($"Failed to send 500 error response: {exInner.Message}")

End Try

Finally

Try

proxyResponse.Close()

Catch finalEx As Exception

Debug.WriteLine($"Error closing proxyResponse: {finalEx.Message}")

End Try

End Sub

End Class

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