I am new to VB...I am using the following code to make an HTTP request and buffer the response into a String:
Try
myHttpWebRequest = CType(WebRequest.Create(strUrl), HttpWebRequest)
myHttpWebResponse = CType(myHttpWebRequest.GetResponse(), HttpWebResponse)
receiveStream = myHttpWebResponse.GetResponseStream()
encode = System.Text.Encoding.GetEncoding("utf-8")
sr = New StreamReader(receiveStream, encode)
Do Until sr.Peek = -1
strLine = String.Concat(strLine, sr.ReadLine)
arrBuff.Add(strLine)
Loop
Catch ex As System.Net.WebException
MsgBox(ex.Message)
Finally
myHttpWebResponse.Close()
End Try
sr.Close()
This works fine, but errors are not handled well, for example if the request triggers a 500 response the VB code encounters an unhandled exception. Any thoughts on how to make this code better?
Use the HttpWebResponse.StatusCode to determine if the server has sent you anything but a (probably) 200 (OK).
Instead of using a MsgBox, raise an exception as follows:
Catch ex As Exception
Throw New Exception(ex.Message)
If you are making an AJAX call from a web page, you can retrieve the message by using:
Catch ex As Exception
HttpContext.Current.Response.Write(ex.Message);
HttpContext.Current.Response.StatusCode = 500;
Related
I'm hitting a 3rd party shipping API and testing bad requests, like a bad ship date. The API accepts an XML request and returns an XML response which may be formatted as an error response. In the case of an error the server returns a status of 400 Bad Request. However my code throws an error at that point and there is no response body. The API folks say they are sending an XML response and a 400 status.
How can I handle (or ignore) the 400 status and receive the xml response?
myRequest = CType(WebRequest.Create(myURL), HttpWebRequest)
myRequest.Method = "POST"
myRequest.ContentType = "application/xml"
myRequest.ContentLength = Data.Length
NewStream = myRequest.GetRequestStream()
NewStream.Write(Data, 0, Data.Length)
NewStream.Close()
Try
myResponse = myRequest.GetResponse() 'Error thrown here
SR = New StreamReader(myResponse.GetResponseStream())
response = SR.ReadToEnd()
Catch ex As Exception
End Try
This works:
Try
myResponse = myRequest.GetResponse()
sr = New StreamReader(myResponse.GetResponseStream())
response = sr.ReadToEnd()
Catch wex As WebException
sr = New StreamReader(wex.Response.GetResponseStream())
response = sr.ReadToEnd()
End Try
I've looked around and couldn't find an answer so I thought i'd ask it here.
I have a program the calls an API with login info passed in the header and the server returns some info upon authentication. The problem is if the user creds are incorrect, the program crashes and throws an exception. The error is 401. How do it catch this, and tell the user?
My code is:
Dim request = TryCast(System.Net.WebRequest.Create("https://myurl.com"), System.Net.HttpWebRequest)
request.Method = "GET"
request.Headers.Add("authorization", "Bearer " + AccessToken)
request.ContentLength = 0
Dim responseContent As String
Using response = TryCast(request.GetResponse(), System.Net.HttpWebResponse)
Using reader = New System.IO.StreamReader(response.GetResponseStream())
responseContent = reader.ReadToEnd()
MessageBox.Show(responseContent)
End Using
End Using
Thanks.
Use a try catch statement
try
'My error prone code
catch ex as Exception
'Handle my error
end try
Try
Dim request = TryCast(System.Net.WebRequest.Create("https://myurl.com"), System.Net.HttpWebRequest)
request.Method = "GET"
request.Headers.Add("authorization", "Bearer " + AccessToken)
request.ContentLength = 0
Dim responseContent As String
Using response = TryCast(request.GetResponse(), System.Net.HttpWebResponse)
Using reader = New System.IO.StreamReader(response.GetResponseStream())
responseContent = reader.ReadToEnd()
MessageBox.Show(responseContent)
End Using
End Using
Catch ex As Exception
MessageBox.Show(ex.ToString(), "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
End Try
Try
.Result = .WebClient.DownloadString(theEnchancedWinClient.PackedScannable)' crash here
Catch ex As Exception
LogEvents(ex.ToString)
End Try
Basically, it crash because of a 503 error when downloading.
But that's stupid. It's a try catch block. Why doesn't it just throw exception gracefully? What should I do?
Following the comment I turn the code into:
Dim strResult = ""
Dim webclient = .WebClient
Try
strResult = webclient.DownloadString(theEnchancedWinClient.PackedScannable)
Catch ex As Exception
LogEvents(ex.ToString)
End Try
Still the program crash and stop there.
If we use webclient.downloadstring on a server with error, we got nothing
Try
result = webClient.DownloadString("https://api.bodis.com/domainclassification?domain=" + CurrentBlog.Domain)
Catch ex As Exception
System.Windows.Forms.Application.DoEvents()
End Try
Usually result contains the response. But in case of error result is empty.
I want to know something. For example, even if the result is bad, usually there is a custom 404 message, etc.
The api.bodis.com is problematic because it mix secure and non secure stuff. However, it gives output anyway in internet explorer. I want to use webclient and I want to know the ouput
Getting ex.response yields nothing
Dim adult = webClient.DownloadString("http://googleads.g.doubleclick.net/apps/domainpark/domainpark.cgi?callback=_google_json_callback&output=js&client=ca-dp-godaddy2_xml&domain_name=" + CurrentBlog.Domain)
'ias.NavigateTillComplete("https://api.bodis.com/domainclassification?domain=" + CurrentBlog.Domain)
Dim result = ""
Dim url = "http://api.bodis.com/domainclassification?domain=" + CurrentBlog.Domain
Dim webRequest = DirectCast(System.Net.HttpWebRequest.Create(url), System.Net.HttpWebRequest)
Dim response As HttpWebResponse
Try
response = DirectCast(webRequest.GetResponse(), HttpWebResponse)
Catch ex As System.Net.WebException
System.Windows.Forms.Application.DoEvents()
response = DirectCast(ex.Response, HttpWebResponse) 'is nothing there
End Try
Dim responseStream = response.GetResponseStream
I am having difficulty getting the response text from a HTTP web request in vb.net when I get a web exception.
This is the code I am doing it with.
Try
myWebResponse = CType(request.GetResponse(), HttpWebResponse)
myStreamReader = New StreamReader(myWebResponse.GetResponseStream())
ResponseText = myStreamReader.ReadToEnd
If myWebResponse.StatusCode = HttpStatusCode.Accepted Or myWebResponse.StatusCode = 200 Then
SendResult = True 'Sent
SendStatus = 1 'message sent successfully
Try
Integer.TryParse(myWebResponse.Headers("Number-Of-MT-PDU"), num_MT_PDU)
Catch ex As Exception
End Try
Else
SendStatus = 2 'message processed but not sent successfully
End If
Catch e As WebException
If (e.Status = WebExceptionStatus.ProtocolError) Then
Dim response As WebResponse = e.Response
Using (response)
Dim httpResponse As HttpWebResponse = CType(response, HttpWebResponse)
statusCode = httpResponse.StatusCode
Try
myStreamReader = New StreamReader(response.GetResponseStream())
Using (myStreamReader)
ResponseText = myStreamReader.ReadToEnd & "Status Description = " & HttpWebResponse.StatusDescription
End Using
Catch ex As Exception
Logger.LogError(Me, ex)
End Try
End Using
Annoyingly, the API I am contacting uses a 404 as a valid response. If I put the request in a browser some message text will be displayed. I want to be able to use that text in my program. I can not simply use the error code to determine actions as I don't think I can differentiate between a valid 404 response and an actual error.
In the code this line
myWebResponse = CType(request.GetResponse(), HttpWebResponse)
throws an exception.
In the exception I can get the 404 code and the description but not the response stream. It is always null.
If I get a 200 response I get the text in the Response stream no problem.
In the web exception response object (in Visual Studios debugger) I have checked the headers and the object values and can't find the response text anywhere. If I stick the request URL in a browser I get response text back even though it is a 404.
The raw response in fiddler:
HTTP/1.1 404 Not Found Connection: close Content-Type: text/plain; charset=UTF-8 Content-Length: 35 "The response Message"
Any ideas on how I can get "The response Message" in my program? I have to use .Net on the server.
Thanks for any help anybody can give.
This LINQPad query works fine, dumping the HTML provided by my web server's "Not Found" error web page:
Dim rq = System.Net.WebRequest.Create(New Uri("http://localhost/test"))
Try
Dim rs = rq.GetResponse
rs.Dump
Catch Ex As System.Net.WebException
Dim rs = Ex.Response
Call (New StreamReader(rs.GetResponseStream)).ReadToEnd.Dump
End Try
FYI Your code works for me, except the presumed typo re HttpWebResponse.StatusDescription (and commenting out "unrelated stuff"), again as a LINQPad query (in .NET 4.0):
Dim request = WebRequest.Create("http://localhost/test")
Dim myStreamReader As StreamReader
Dim SendStatus As Integer = -1
Dim statusCode As HttpStatusCode
Dim ResponseText As String
Try
Dim myWebResponse = CType(request.GetResponse(), HttpWebResponse)
myStreamReader = New StreamReader(myWebResponse.GetResponseStream())
ResponseText = myStreamReader.ReadToEnd
If myWebResponse.StatusCode = HttpStatusCode.Accepted Or myWebResponse.StatusCode = 200 Then
'SendResult = True 'Sent
SendStatus = 1 'message sent successfully
'Try
' Integer.TryParse(myWebResponse.Headers("Number-Of-MT-PDU"), num_MT_PDU)
'Catch ex As Exception
'End Try
Else
SendStatus = 2 'message processed but not sent successfully
End If
Catch e As WebException
If (e.Status = WebExceptionStatus.ProtocolError) Then
Dim response As WebResponse = e.Response
Using (response)
Dim httpResponse As HttpWebResponse = CType(response, HttpWebResponse)
statusCode = httpResponse.StatusCode
Try
myStreamReader = New StreamReader(response.GetResponseStream())
Using (myStreamReader)
ResponseText = myStreamReader.ReadToEnd & "Status Description = " & httpResponse.StatusDescription ' HttpWebResponse.StatusDescription
End Using
Catch ex As Exception
'Logger.LogError(Me, ex)
ex.Dump("Exception")
End Try
End Using
End If
End Try
ResponseText.Dump("ResponseText")
I have also confirmed the above code (with the inferred As clauses added and converting the .Dump calls to Console.WriteLine) works in .NET 2.0 with VB8.
Note that the key is that even though the act of GetResponseStream() throws a .NET WebException, the HttpWebResponse is actually passed to the WebException object, so when in the Catch, you do a new GetResponseStream() on the WebException.Response object.
Below, very similar code for when in the Catch of the initial GetResponseStream()
Try
OriginalResponseStream = GetResponseStream(OriginalHTTPWebResponse)
Catch wex as WebException
Dim response As WebResponse = wex.Response
Dim statusCode As HttpStatusCode
Dim ResponseText As String
Dim httpResponse As HttpWebResponse = CType(response, HttpWebResponse)
statusCode = httpResponse.StatusCode
Try
Dim myStreamReader As New StreamReader(response.GetResponseStream())
Using (myStreamReader)
ResponseText = myStreamReader.ReadToEnd
Process(ResponseText) '<===as in whatever you need to do with the response
End Using
Catch ex As Exception
HandleIt(ex.Message) '<===as in whatever you want to do if Exception during the above
End Try
End Try