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