VB .NET Http Post Request Program Example

Create a new class library project and you might want to use HttpPostRequestVB as the project and solution names.

Imports System

Imports System.Net

Imports System.IO

Imports System.Text

Imports System.Web

' Simple class that encapsulates the HTTP post sample.

Public Class HttpPostRequest

    ' Displays simple usage information.       

    Shared Sub usage()

        Console.WriteLine("Executable_file_name [-u URL] [-d data] [-s file] [-p proxy]")

        Console.WriteLine("Available options:")

        Console.WriteLine("     -u URL          URL to post data to")

        Console.WriteLine("     -d data         Data to post")

        Console.WriteLine("     -s file         File name to save response to")

        Console.WriteLine("     -p HTTP URL     Proxy to use for post operation")

        Console.WriteLine()

    End Sub

    ' This routine validates the data being posted to the web page. It parses

    ' the string for reserved characters '?', '=', and '&'. The individual

    ' validated parts are returned via a StringBuilder object.       

    ' <param name="postData">Data to validate</param>

    ' <returns>StringBuilder object representing the parsed elements</returns>

    Public Function ValidatePostData(ByVal postData As String) As StringBuilder

        Dim encodedPostData As StringBuilder = New StringBuilder()

        ' These characters should be more out there...

        Dim reservedChars() As Char = {"?", "=", "&", "+"}

        Dim pos As Integer

        Dim offset As Integer

        ' Validate the data to be posted

        Console.WriteLine("Validating the data to be posted...")

        offset = 0

        While (offset < postData.Length)

            pos = postData.IndexOfAny(reservedChars, offset)

            If (pos = -1) Then

                ' Append the remaining part of the string

                Console.WriteLine("Appending the remaining part of the string...")

                encodedPostData.Append(HttpUtility.UrlEncode( _

                    postData.Substring(offset, postData.Length - offset)))

                Exit While

            End If

            ' Found a special character so append up to the special character

            Console.WriteLine("Found a special character so append up to the special character...")

            encodedPostData.Append(HttpUtility.UrlEncode( _

                postData.Substring(offset, pos - offset)))

            encodedPostData.Append(postData.Substring(pos, 1))

            offset = pos + 1

        End While

        ValidatePostData = encodedPostData

    End Function

    ' This method creates an HttpWebRequest object, sets the method to "POST",

    ' and builds the data to post. Once the HttpWebRequest object is created,

    ' the request stream is obtained and the post data is sent and the

    ' request stream closed. The response is then retrieved.       

    ' <param name="postUrl">URL to post data to</param>

    ' <param name="postData">Data to post</param>

    ' <param name="proxyServer">Proxy server to use</param>

    ' <param name="saveFile">Filename to save response to</param>

    Public Sub HttpMethodPost( _

        ByVal postUrl As String, _

        ByVal postData As String, _

        ByVal proxyServer As IWebProxy, _

        ByVal saveFile As String)

        Dim httpRequest As HttpWebRequest = Nothing

        Dim httpResponse As HttpWebResponse = Nothing

        Dim httpPostStream As Stream = Nothing

        Dim httpResponseStream As BinaryReader = Nothing

        Dim localFile As FileStream = Nothing

        Try

            Dim encodedPostData As StringBuilder

            Dim postBytes() As Byte = Nothing

            ' Create HTTP web request

            Console.WriteLine("Creating HTTP web request...")

            httpRequest = CType(WebRequest.Create(postUrl), HttpWebRequest)

            ' Change method from the default "GET" to "POST"

            Console.WriteLine("Changing method from the default GET to POST...")

            httpRequest.Method = "POST"

            ' Posted forms need to be encoded so change the content type  

            Console.WriteLine("Changing the content type (encoding)...")

            httpRequest.ContentType = "application/x-www-form-urlencoded"

            ' Set the proxy

            Console.WriteLine("Setting the proxy...")

            httpRequest.Proxy = proxyServer

            ' Validate and encode the data to POST

            Console.WriteLine("Validating and encode the data to POST...")

            encodedPostData = ValidatePostData(postData)

            Console.WriteLine("Encoded POST string: '{0}'", encodedPostData.ToString())

            ' Retrieve a byte array representation of the data

            Console.WriteLine("Retrieving a byte array representation of the data...")

            postBytes = Encoding.UTF8.GetBytes(encodedPostData.ToString())

            ' Set the content length (the number of bytes in the POST request)

            Console.WriteLine("Setting the content length - the number of bytes in the POST request...")

            httpRequest.ContentLength = postBytes.Length

            ' Retrieve the request stream so we can write the POST data

            Console.WriteLine("Retrieving the request stream so we can write the POST data...")

            httpPostStream = httpRequest.GetRequestStream()

            ' Write the POST request

            Console.WriteLine("Writing the POST request...")

            httpPostStream.Write(postBytes, 0, postBytes.Length)

            httpPostStream.Close()

            httpPostStream = Nothing

            ' Retrieve the response

            Console.WriteLine("Retrieving the response...")

            httpResponse = CType(httpRequest.GetResponse(), HttpWebResponse)

            ' Retrieve the response stream

            Console.WriteLine("Retrieving the response stream...")

            httpResponseStream = New BinaryReader( _

                httpResponse.GetResponseStream(), _

                Encoding.UTF8 _

                )

            Dim readData() As Byte

            ' Open the file to save the response to

            Console.WriteLine("Opening the file to save the response to...")

            localFile = File.Open( _

                saveFile, _

                System.IO.FileMode.Create, _

                System.IO.FileAccess.Write, _

                System.IO.FileShare.None _

                )

            Console.WriteLine("Saving response to: {0}", localFile.Name)

            Console.WriteLine("Receiving response...")

            ' Receive the response stream until the end

            Console.WriteLine("Receiving the response stream until the end...")

            Dim count As Integer = 0

            Dim percent As Long

            While (True)

                readData = httpResponseStream.ReadBytes(4096)

                If (readData.Length = 0) Then

                    Exit While

                End If

                localFile.Write(readData, 0, readData.Length)

                ' Calculate the progress and display to the console

                count += readData.Length

                percent = (count * 100) / httpResponse.ContentLength

                ' Console.WriteLine(" ")

                Console.WriteLine("{0}% progress...", percent.ToString().PadLeft(2))

            End While

            Console.WriteLine()

        Catch wex As WebException

            Console.WriteLine("Exception occurred: {0}", wex.ToString())

            httpResponse = CType(wex.Response, HttpWebResponse)

        Finally

            ' Close any remaining resources

            Console.WriteLine("Closing any remaining resources...")

            If (Not IsNothing(httpResponse)) Then

                httpResponse.Close()

            End If

            If (Not IsNothing(localFile)) Then

                localFile.Close()

            End If

        End Try

    End Sub

    ' This is the main routine that parses the command line and calls routines to

    ' issue the POST request and receive the response.

    ' <param name="args">Command line arguments</param>

    Shared Sub Main()

        Dim proxyServer As IWebProxy

        Dim uriToPost As String = "http://search.msdn.microsoft.com/"

        Dim proxyName As String = Nothing

        Dim postData As String = "Default.aspx?Query=web.dll"

        Dim fileName As String = Nothing

        ' Parse the command line

        Dim args As String() = Environment.GetCommandLineArgs()

        Dim i As Integer

        usage()

        For i = 1 To args.GetUpperBound(0)

            Try

                Dim CurArg() As Char = args(i).ToCharArray(0, args(i).Length)

                If (CurArg(0) = "-") Or (CurArg(0) = "/") Then

                    Select Case Char.ToLower(CurArg(1), System.Globalization.CultureInfo.CurrentCulture)

                        Case "u"

                            ' URI to post to

                            i = i + 1

                            uriToPost = args(i)

                        Case "p"

                            ' Name of proxy server to use

                            i = i + 1

                            proxyName = args(i)

                        Case "d"

                            ' Retrieve all referenced images and text on the same host

                            i = i + 1

                            postData = args(i)

                        Case "s"

                            ' Local save path to append to retrieved resources

                            i = i + 1

                            fileName = args(i)

                        Case Else

                            usage()

                            Exit Sub

                    End Select

                End If

            Catch e As Exception

                usage()

                Exit Sub

            End Try

        Next

        Try

            Dim httpPost As HttpPostRequest = New HttpPostRequest()

            ' Set the proxy if supplied or use the default IE static proxy

            Console.WriteLine("Setting the proxy if supplied or use the default IE static proxy...")

            If (IsNothing(proxyName)) Then

                proxyServer = WebRequest.DefaultWebProxy

            Else

                ' Must cast it to IWebProxy if needed, not done here

                proxyServer = New WebProxy(proxyName)

            End If

            ' Post the request and write the response to the file

            Console.WriteLine("Posting the request and write the response to the file...")

            httpPost.HttpMethodPost(uriToPost, postData, proxyServer, fileName)

        Catch ex As Exception

            Console.WriteLine("Exception occurred: {0}", ex.Message)

        End Try

    End Sub

End Class