I have the following function which i use to get html source from my website
Public Function GetPageHTML(ByVal URL As String, _
Optional ByVal TimeoutSeconds As Integer = 10) _
As String
' Retrieves the HTML from the specified URL,
' using a default timeout of 10 seconds
Dim objRequest As Net.WebRequest
Dim objResponse As Net.WebResponse
Dim objStreamReceive As System.IO.Stream
Dim objEncoding As System.Text.Encoding
Dim objStreamRead As System.IO.StreamReader
Try
' Setup our Web request
objRequest = Net.WebRequest.Create(URL)
objRequest.Timeout = TimeoutSeconds * 1000
' Retrieve data from request
Try
objResponse = objRequest.GetResponse 'some times it gives an error server unavailable 503
Catch ex As WebException
MsgBox(ex.Message)
End Try
objStreamReceive = objResponse.GetResponseStream
objEncoding = System.Text.Encoding.GetEncoding( _
"utf-8")
objStreamRead = New System.IO.StreamReader( _
objStreamReceive, objEncoding)
' Set function return value
GetPageHTML = objStreamRead.ReadToEnd()
' Check if available, then close response
If Not objResponse Is Nothing Then
objResponse.Close()
End If
Catch
' Error occured grabbing data, simply return nothing
Return ""
End Try
End Function
some times the objResponse gives error "503 Server unavailable" and many other errors like 403 and so on, how can i handle each of those errors independently?
how can i make this function retry the request after sometime? problem is the try statement doesn't seem to handle this and i am not sure why i don't see the exception MsgBox but it shows the error on the debugger.
Cast the response as a HttpWebResponse object and do a Select Case of it's StatusCode Property. You'll have to clean and finish this up, but here is an example:
Select Case CType(objResponse, Net.HttpWebResponse).StatusCode
Case Net.HttpStatusCode.InternalServerError
'This is sloppy, but a quick example for one of your sub-questions.
System.Threading.Thread.Sleep(10000)
'Try again.
objResponse = objRequest.GetResponse
Case Net.HttpStatusCode.BadRequest
'Error Handling
Case Net.HttpStatusCode.OK
'Proceed as normal.
Case Else
'Error Handling
End Select
Related
I need help uploading the file to Google Drive.
Everything works fine but with an error during first trial.
During the debug at request.upload the cursor don't wait (wait for the file to upload) and skips to the next line Dim responsefile As New Data.File and I get nothing in request.ResponseBody.
After that I run the function cursor actually waits on request.upload and it uploads file successfully.
I don't know what is actually happening. I checked the data every time and it is the same.
Public Async Function UploadFile3(service As DriveService, FilePath As String) As Tasks.Task(Of Data.File)
If service3.ApplicationName <> "netGDriveApi" Then CreateService()
If IO.File.Exists(FilePath) Then
Dim body As New Data.File()
body.Name = IO.Path.GetFileName(FilePath)
body.Description = "BackUP file"
body.MimeType = "application/octet-stream"
'body.FileExtension = ".bak"
'-------------------------------------------------UPLOAD FILE PROCESS-------------------------------------------------------------
Dim byteArray As Byte() = IO.File.ReadAllBytes(FilePath)
Dim stream As New IO.MemoryStream(byteArray)
Try
Dim request As FilesResource.CreateMediaUpload = service.Files.Create(body, stream, body.MimeType)
Await request.UploadAsync() 'Cursor skips first time here and dont wait for response.
Dim responsefile As New Data.File 'Cursor waits from the above step to here till the file uploaded.
responsefile = request.ResponseBody
If IsNothing(responsefile) Then
MessageBox.Show("Try Again")
Else
MessageBox.Show(responsefile.Id.ToString)
End If
Catch e As Exception
MessageBox.Show("An error occurred: " + e.Message)
Return Nothing
End Try
Else
MessageBox.Show("FILE DOES NOT EXISTS." + FilePath)
Return Nothing
End If
End Function
request.UploadAsync() returns a Task(Of IUploadProgress). At the very least, you should be examining the result of this task. It might give you clues as to the cause of your problems.
For example, while debugging you could do something like the following:
Try
Dim request As FilesResource.CreateMediaUpload = service.Files.Create(body, stream, body.MimeType)
Dim Upload As IUploadProgress = Await request.UploadAsync() 'Cursor skips first time here and dont wait for response.
If Upload.Status <> UploadStatus.Completed Then
Dim ex As Exception = Upload.Exception
MessageBox.Show(ex.Message, "UploadAsync Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
Return Nothing
Else
MessageBox.Show(Upload.Status.ToString, "Upload Status:")
End If
Dim responsefile As New Data.File 'Cursor waits from the above step to here till the file uploaded.
responsefile = request.ResponseBody
Always check what information methods return, and use that information as necessary in your production code.
The line Dim request As FilesResource.CreateMediaUpload = service.Files.Create(body, stream, body.MimeType). Problem is here.
Thanks to #stevec to guide me the error.
The drive service is service3 and in the above line its just written service.Files.Create.
So the actual rectified answer is
Dim request As FilesResource.CreateMediaUpload = service3.Files.Create(body, stream, body.MimeType)
I'm trying to make a simple client-side application to recieve small text data, compare it and then does something on client machine depending on what server sent.
Server Logic: The server side is made in java, so can't change anything there. Server sends string "abc001" on connecting to client.
Client Logic: Client recieves the string "abc001" from server & checks if it's recieved string is the same as "abc001", then does something accordingly.
Problem: When the client recieves data, I display it in msgbox. But instead of just "abc001", there pops up an extra blank msgbox(image included).
Client Code - On Start:
Try
' declare vals
Dim ip As String = "127.0.0.1"
Dim port As Integer = 5000
' set client
_client = New TcpClient(ip, port)
' disable cross thread calls checking
CheckForIllegalCrossThreadCalls = False
' recieve msg
Threading.ThreadPool.QueueUserWorkItem(AddressOf RecieveMessages)
Catch ex As Exception
MsgBox(ex.ToString)
End Try
Client Code - Recieve Data
Private Sub RecieveMessages(state As Object)
Try
While True
Dim ns As NetworkStream = _client.GetStream()
Dim toRecieve(_client.ReceiveBufferSize) As Byte
ns.Read(toRecieve, 0, CInt(_client.ReceiveBufferSize))
Dim txt As String = Encoding.ASCII.GetString(toRecieve)
MsgBox(txt)
End While
Catch ex As Exception
MsgBox(ex.ToString)
End Try
End Sub
MsgBox 1
MsgBox 2
How to not get the blank msgbox. Even when compared, the data recived does not match parameters. Tried to use delay, tried fixing the buffer size to 6 bytes but no use.. Any help is appreciated. Thanks.
EDIT 1: Tried my best to figure it out but can't.. Tried cleaning the returned string data and even tried storing each return data in array. Saw the stack and it says the msgbox has "nothing" in it. It's null.. I don't even know what to do.. Here's the code for strings clean:
Private Sub RecieveMessages(state As Object)
Dim message(0) As String
Dim command_raw, command_clean, command As String
Dim counter As Integer = 0
Try
While True
Dim ns As NetworkStream = _client.GetStream()
Dim toRecieve(_client.ReceiveBufferSize) As Byte
ns.Read(toRecieve, 0, CInt(_client.ReceiveBufferSize))
Dim txt As String = Encoding.ASCII.GetString(toRecieve)
message(0) = txt
command_raw = message(0)
command_clean = command_raw.Replace(vbCrLf, Nothing)
command = command_clean.Substring(0, 6)
MsgBox(command)
End While
Catch ex As Exception
MsgBox(ex.ToString)
End Try
End Sub
I am working on a program and uploads a shipping manifest to a the shippers website. When I try to upload, I get a nondescript error back from their server, and when checking with the shipper, they tell me that "there is an issue with the SSL" I am using.
I've spent quite a bit of time piecing together code that, from what I seem to understand, is supposed to work, but I'm not making any progress. As far as I know everything else is fine with the upload, but there is a problem with my SSL certificate
If I understand what this code is supposed to do correctly, I should get a certificate from the shippers website, which allows certification to my program for a space of time during which I can upload the data. I'm really not sure that this is what my code is doing at all, but the only code examples I have seen show it something like this.
Here's my code with the URLs changed:
'This references a custom class that compiles the manifest I'm going to upload
Dim StringToUpload As String = Compile_Manifest(MyDate, UseTestDB)
Dim webClient As New System.Net.WebClient
webClient.Credentials = System.Net.CredentialCache.DefaultCredentials
'From what I understand,
'this is supposed to set up properties used in next section of code
System.Net.ServicePointManager.SecurityProtocol = Net.SecurityProtocolType.Ssl3
System.Net.ServicePointManager.ServerCertificateValidationCallback = _
AddressOf AcceptAllCertifications
'I can see that this reaches the server,
'but I don't know how it relates to the next section of code
'that actually uploads the manifest
Dim ServerRequest As System.Net.WebRequest = _
System.Net.WebRequest.Create("https://www.certify.some-shippper.com:443/somefolder")
Dim ServerResponse As System.Net.WebResponse
ServerResponse = ServerRequest.GetResponse()
ServerResponse.Close()
'This code works for the upload of the manifest,
'and it seems the above code is unrelated and does not use a SSL certificate.
'When this code runs I get the same error back from the shippers server,
'indicating an issue with my SSL, with or without the two sections of code above.
Dim StrResult As String = ""
Dim WrappedString As String = TransmitPLD.WrapPldFile(StringToUpload)
'This references a custom class that wraps the data to upload
'in information from the shipper.
Dim ByesToUpload As Byte() = _
System.Web.HttpUtility.UrlEncodeToBytes(WrappedString, _
System.Text.ASCIIEncoding.ASCII)
Dim Result As Byte() = _
webClient.UploadData("https://www.certify.some-shippper.com:443/somefolder", _
ByesToUpload)
StrResult = System.Web.HttpUtility.UrlDecode(Result, _
System.Text.ASCIIEncoding.ASCII)
MessageBox.Show(StrResult)
So it turns out I went about it the wrong way. I needed to upload my data through System.Net.WebRequest and it takes care of the certificates for me. Not implementing all the parts of the code I needed, it didn't handle the retrieval of the shipper's certificate.
In case anyone else gets confused about the matter like I did, here's my working code for anyone to see, adapt and use. My resource for fixing the code (and by that I mean starting from scratch) was the MSDN page for the WebRequest class, and it has code examples much the same as what I have below in C++, C#, and VB.NET and here is the link.
First there are some global variables that need to be set and class that needs to be created for to store the upload response:
' This is set in the function that Upload function
' and uploads the data in the ReadCallback sub
Private Shared WrappedString As String
' This is used to wait for the callback in the Upload function
Private Shared allDone As New Threading.ManualResetEvent(False)
Friend Class RequestState
' This class stores the request state of the request.
Public request As Net.WebRequest
Public Sub New()
request = Nothing
End Sub ' New
End Class ' RequestState
Then there is a sub needed for the upload part web request which will be called further below in the upload function:
Private Shared Sub ReadCallback(asynchronousResult As IAsyncResult)
Try
Dim myRequestState As RequestState = CType(asynchronousResult.AsyncState, RequestState)
Dim myWebRequest As Net.WebRequest = myRequestState.request
' End the request.
Dim streamResponse As IO.Stream = myWebRequest.EndGetRequestStream(asynchronousResult)
' Convert the string into a byte array.
Dim byteArray As Byte() = System.Text.Encoding.ASCII.GetBytes(WrappedString)
' Write the data to the stream.
streamResponse.Write(byteArray, 0, byteArray.Length)
streamResponse.Close()
' Allow the main thread to resume.
allDone.Set()
Catch ex As Exception
Throw New Exception("Error in " & Reflection.MethodBase.GetCurrentMethod.Name.ToString & " **" & ex.Message, ex)
End Try
End Sub ' ReadCallback
Finally, this is the function that should be called to upload the data, which uses all the code above:
Public Shared Function Upload(ByVal MyDate As Date) As String
Dim StrResult As String = ""
UploadSucess = False
Try
' This is my code that builds the manifest that I want to upload
Dim StringToUpload As String = Compile_PLD200(MyDate)
WrappedString = TransmitPLD.WrapPldFile(StringToUpload)
Dim myWebRequest As Net.WebRequest
myWebRequest = Net.WebRequest.Create("https://www.some.website.com:443/someplace")
' Create an instance of the RequestState and assign
' myWebRequest to it's request field.
Dim myRequestState As New RequestState()
myRequestState.request = myWebRequest
myWebRequest.ContentType = "multipart/mixed; boundary=BOUNDARY"
myRequestState.request.Method = "POST"
' Start the asynchronous 'BeginGetRequestStream' method call.
Dim r As IAsyncResult = CType(myWebRequest.BeginGetRequestStream(AddressOf ReadCallback, myRequestState), IAsyncResult)
' Pause the current thread until the async operation completes.
allDone.WaitOne()
' Send the Post and get the response.
Dim myWebResponse As Net.WebResponse = myWebRequest.GetResponse()
Dim streamResponse As IO.Stream = myWebResponse.GetResponseStream()
Dim streamRead As New IO.StreamReader(streamResponse)
Dim readBuff(256) As [Char]
Dim count As Integer = streamRead.Read(readBuff, 0, 256)
While count > 0
Dim outputData As New [String](readBuff, 0, count)
Console.WriteLine(outputData)
count = streamRead.Read(readBuff, 0, 256)
StrResult += outputData
End While
' Close the Stream Object.
streamResponse.Close()
streamRead.Close()
' Release the HttpWebResponse Resource.
myWebResponse.Close()
Catch ex As Exception
Throw New Exception("Error in " & Reflection.MethodBase.GetCurrentMethod.Name.ToString & " **" & ex.Message, ex)
End Try
Return StrResult
End Function ' Upload
Again here is the MSDN page for the WebRequest class which has a code example too.
Hope this helps anyone who was stuck like I was. And any criticisms as to the implementation of the code are welcome. This just happen to do what I want, I can't say it is the most efficient implementation.
I am coding a whitelist for my application in VB.NET.
I am using the HttpWebRequest Method and HttpWebResponse.
If the Whitelist Host is down, the whitelist is bypassed and the program is available to anyone which is a vulnerability.
Public Function GetWhitelist(ByVal PageURL As String) As String
Dim S As String = ""
Try
Dim Request As HttpWebRequest = WebRequest.Create("WHITELIST URL HERE")
Dim Response As HttpWebResponse = Request.GetResponse()
Using Reader As StreamReader = New StreamReader(Response.GetResponseStream())
S = Reader.ReadToEnd
End Using
Catch ex As Exception
Debug.WriteLine("Start Program Error. Handle:0")
End Try
Return S
End Function
I want to give the user an error if the website is down, any ideas?
Regards.
What is your error condition? This function alone doesn't prevent anything from happening in the event of an exception. The function still exits with returning a string. So any consuming code would have to look for error conditions and handle them accordingly.
If the request fails, you should meaningfully handle the exception. Two ideas off the top of my head would include:
1) Let the exception bubble up the stack:
Public Function GetWhitelist(ByVal PageURL As String) As String
Dim S As String = ""
Dim Request As HttpWebRequest = WebRequest.Create("WHITELIST URL HERE")
Dim Response As HttpWebResponse = Request.GetResponse()
Using Reader As StreamReader = New StreamReader(Response.GetResponseStream())
S = Reader.ReadToEnd
End Using
Return S
End Function
This would make the attempt to contact the host and, if that attempt failed, throw an exception instead of return a string.
2) Throw a custom exception:
Public Function GetWhitelist(ByVal PageURL As String) As String
Dim S As String = ""
Try
Dim Request As HttpWebRequest = WebRequest.Create("WHITELIST URL HERE")
Dim Response As HttpWebResponse = Request.GetResponse()
Using Reader As StreamReader = New StreamReader(Response.GetResponseStream())
S = Reader.ReadToEnd
End Using
Catch ex As Exception
Debug.WriteLine("Start Program Error. Handle:0")
Throw New SomeCustomException(String.Format("Unable to contact host: {0}", PageURL), ex)
End Try
Return S
End Function
This would provide a more targeted exception instead of whatever comes out of the response reader, would provide useful runtime information about the error for logging and analysis (namely the runtime value of the PageURL), and takes a step toward hiding the implementation details from code outside of this object (since that code doesn't really care about the HttpWebRequest and HttpWebResponse, it just wants to know if the URL is good or not).
Remember that throwing an exception is a perfectly acceptable exit path for a function. It doesn't always have to return a value. An exception is an appropriate way of indicating an error condition. Your current implementation, however, "swallows" the exception and provides no indication to the consuming code that anything went wrong. Instead it returns a "magic value" of String.Empty which consuming code may or may not ignore.
Change your exception handler. The correct way to do this is to just try the request and handle the exception if it fails.
in the following code i am trying to handle different server resposes:
this function is used to read xml or html soruce from a web page
and in the commented line i get "Object reference not set to an instance of an object."
i wonder why.
Public Function GetPageHTML(ByVal URL As String, _
Optional ByVal TimeoutSeconds As Integer = 10) _
As String
' Retrieves the HTML from the specified URL,
' using a default timeout of 10 seconds
Dim objRequest As Net.WebRequest
Dim objResponse As Net.WebResponse
Dim objStreamReceive As System.IO.Stream
Dim objEncoding As System.Text.Encoding
Dim objStreamRead As System.IO.StreamReader
Try
' Setup our Web request
objRequest = Net.WebRequest.Create(URL)
objRequest.Timeout = TimeoutSeconds * 1000
' Retrieve data from request
Select Case CType(objResponse, Net.HttpWebResponse).StatusCode 'Here is where i get the error Object reference not set to an instance of an object.
Case Net.HttpStatusCode.InternalServerError
'This is sloppy, but a quick example for one of your sub-questions.
System.Threading.Thread.Sleep(10000)
'Try again.
objResponse = objRequest.GetResponse
Case Net.HttpStatusCode.BadRequest
'Error Handling
Case Net.HttpStatusCode.OK
'Proceed as normal.
Case Else
'Error Handling
End Select
objStreamReceive = objResponse.GetResponseStream
objEncoding = System.Text.Encoding.GetEncoding( _
"utf-8")
objStreamRead = New System.IO.StreamReader( _
objStreamReceive, objEncoding)
' Set function return value
GetPageHTML = objStreamRead.ReadToEnd()
' Check if available, then close response
If Not objResponse Is Nothing Then
objResponse.Close()
End If
Catch
' Error occured grabbing data, simply return nothing
Return ""
End Try
End Function
now when i remove the switch statement and just write the objResponse as
objResponse = objRequest.GetResponse
except i get an exception of error 403 or 503, i don't know how to handle this.
Your error line:
Select Case CType(objResponse, Net.HttpWebResponse).StatusCode
is called without ever assigning anything to objResponse.
You need to change it to:
objResponse = objRequest.GetResponse
Select Case CType(objResponse, Net.HttpWebResponse).StatusCode`
In regards to getting HTTP error codes for the page you are trying to ftech, here are the meanings of them and their causes:
http://en.wikipedia.org/wiki/List_of_HTTP_status_codes
First off, tcarvin is correct, your question's code is missing this line:
objResponse = objRequest.GetResponse
Secondly, you can do this to resolve your other issue:
If Not objResponse Is Nothing Then
'Select Case Code
Else
'Handle failure.
End If