Handling Errors from HttpWebRequest.GetResponse

Question

Hey experts -

I'm having a ridiculous time trying to get an SMS API working (ZeepMobile, if you're interested) with .NET... I've been around .NET for a few years, but with all this social networking and API stuff, I need to get into the HttpWebRequest a bit. I'm new at it, but not completely new; I was able to hook up my site to Twitter without too much fuss (ie, I was able to modify someone's code to work for me).

Anyways, the way their API works is to send an SMS message, you send them a POST and they respond back to you. I can send it just fine, but every time I do, rather than echo back something helpful to figure out what the error is, I get the Yellow Error Page Of Death (YEPOD) saying something to the effect of "The remote server returned an error: (400) Bad Request." This occurs on my line:

'...creation of httpwebrequest here...'
Dim myWebResponse As WebResponse
myWebResponse = request.GetResponse() '<--- error line

Is there any way to simply receive the error from the server rather than have the webserver throw an exception and give me the YEPOD?

Or better yet, can anyone post a working example of their Zeep code? :)

Thanks!

EDIT: Here's my whole code block:

Public Shared Function SendTextMessage(ByVal username As String, _
ByVal txt As String) As String
 Dim content As String = "user_id=" + _
username + "&body=" + Current.Server.UrlEncode(txt)

 Dim httpDate As String = DateTime.Now.ToString("r")
 Dim canonicalString As String = API_KEY & httpDate & content

 Dim encoding As New System.Text.UTF8Encoding
 Dim hmacSha As New HMACSHA1(encoding.GetBytes(SECRET_ACCESS_KEY))

 Dim hash() As Byte = hmacSha.ComputeHash(encoding.GetBytes(canonicalString))
 Dim b64 As String = Convert.ToBase64String(hash)

 'connect with zeep'
 Dim request As HttpWebRequest = CType(WebRequest.Create(_
"https://api.zeepmobile.com/messaging/2008-07-14/send_message"), HttpWebRequest)
 request.Method = "POST"
 request.ServicePoint.Expect100Continue = False

 ' set the authorization levels'
 request.Headers.Add("Authorization", "Zeep " & API_KEY & ":" & b64)
 request.ContentType = "application/x-www-form-urlencoded"
 request.ContentLength = content.Length

 ' set up and write to stream'
 Dim reqStream As New StreamWriter(request.GetRequestStream())
 reqStream.Write(content)
 reqStream.Close()
 Dim msg As String = ""
 msg = reqStream.ToString

 Dim myWebResponse As WebResponse
 Dim myResponseStream As Stream
 Dim myStreamReader As StreamReader

 myWebResponse = request.GetResponse()

 myResponseStream = myWebResponse.GetResponseStream()
 myStreamReader = New StreamReader(myResponseStream)
 msg = myStreamReader.ReadToEnd()
 myStreamReader.Close()
 myResponseStream.Close()

 ' Close the WebResponse'
 myWebResponse.Close()
 Return msg
End Function

Answer 1

I think it's normal for a WebException to be thrown when the request returns a 4xx or 5xx code. You just need to catch it and handle it appropriately.

Have you looked at the Headers collection after the call to GetResponse?

it just throws an exception at the GetResponse... how would I check the headers after that?

Try
    myWebResponse = request.GetResponse()
Catch x As WebException
    log, cleanup, etc.
Finally
    log/inspect headers?
End Try

Answer 2

Try this:

Dim req As HttpWebRequest = DirectCast(WebRequest.Create(url), HttpWebRequest)
'' set up request
Try
    Using response = req.GetResponse()
        '' success in here
    End Using
Catch ex As WebException
    Console.WriteLine(ex.Status)
    If ex.Response IsNot Nothing Then
        '' can use ex.Response.Status, .StatusDescription
        If ex.Response.ContentLength <> 0 Then
            Using stream = ex.Response.GetResponseStream()
                Using reader = New StreamReader(stream)
                    Console.WriteLine(reader.ReadToEnd())
                End Using
            End Using
        End If
    End If
End Try

---

C# version

HttpWebRequest req = (HttpWebRequest) WebRequest.Create(url);
// set up request
try {
    using (var response = req.GetResponse()) {
        // success in here
        }
}
catch (WebException ex) {
    Console.WriteLine(ex.Status);
    if (ex.Response != null) {
        // can use ex.Response.Status, .StatusDescription
        if (ex.Response.ContentLength != 0) {
            using (var stream = ex.Response.GetResponseStream()) {
                using (var reader = new StreamReader(stream)) {
                    Console.WriteLine(reader.ReadToEnd());
                }
            }
        }
    }    
}

---

Here's your code, modified a bit:

Try
    'connect with zeep'
    Dim request As HttpWebRequest = CType(WebRequest.Create( _
"https://api.zeepmobile.com/messaging/2008-07-14/send_message"), HttpWebRequest)
    request.Method = "POST"
    request.ServicePoint.Expect100Continue = False

    ' set the authorization levels'
    request.Headers.Add("Authorization", "Zeep " & API_KEY & ":" & b64)
    request.ContentType = "application/x-www-form-urlencoded"
    request.ContentLength = content.Length

    ' set up and write to stream'
    Using requestStream As Stream = request.GetRequestStream()
        Using requestWriter As New StreamWriter(requestStream)
            requestWriter.Write(content)
        End Using
    End Using

    Using myWebResponse As WebResponse = request.GetResponse()
        Using myResponseStream As Stream = myWebResponse.GetResponseStream()
            Using myStreamReader As StreamReader = New StreamReader(myResponseStream)
                Return myStreamReader.ReadToEnd()
            End Using
        End Using
    End Using
Catch ex As WebException
    Console.WriteLine(ex.Status)
    If ex.Response IsNot Nothing Then
        '' can use ex.Response.Status, .StatusDescription
        If ex.Response.ContentLength <> 0 Then
            Using stream = ex.Response.GetResponseStream()
                Using reader = New StreamReader(stream)
                    Console.WriteLine(reader.ReadToEnd())
                End Using
            End Using
        End If
    End If
End Try

---

Dumping headers:

Dim headers As WebHeaderCollection = request.Headers
' Displays the headers. Works with HttpWebResponse.Headers as well
Debug.WriteLine(headers.ToString())

' And so does this
For Each hdr As String In headers
    Dim headerMessage As String = String.Format("{0}: {1}", hdr, headers(hdr))
    Debug.WriteLine(headerMessage)
Next

Answer 3

I am using the same code, but can anybody explain me why im getting response.ContentLength as 0 always.....