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WebResourceProvider VB.NET style

, 30 Aug 2002
Ravi Bhavnani's WebResourceProvider ported to the .NET Framework
Imports System.Net
Imports System.Net.Sockets
Imports System.IO
Imports System.Text

Public MustInherit Class WebResourceProvider

    ' WebResourceProvider.vb
    '
    ' Written by Marcel Spring, ADVIS AG, Switzerland <marcel.spring@advis.ch>
    ' Copyright (c) 2002.  All Rights Reserved.
    '
    ' code adapted from original c++ library from
    ' Ravi Bhavnani <ravib@ravib.com>
    ' http:'www.codeproject.com/internet/WebResourceProvider.asp.
    ' Copyright (c) 2002.  All Rights Reserved.
    '
    ' This code may be used in compiled form in any way you desire. This
    ' file may be redistributed unmodified by any means PROVIDING it is 
    ' not sold for profit without the author's written consent, and 
    ' providing that this notice and the author's name and all copyright 
    ' notices remains intact. 
    '
    ' An email letting us know how you are using it would be nice as well. 
    '
    ' This code is provided "as is" with no expressed or implied warranty.
    ' The author accepts no liability for any damage/loss of business that
    ' this product may cause.
    '
    '
    ' Revision history:
    '
    ' 06 Jun 2002 - Initial release
    ' 22 Aug 2002 - Version 1.1
    '               - RemoveHTML is now treating special characters like Umlaut etc. well
    '               - ReplaceSpecialChars function added
    '               - StoreIndex function added, to store the current pointer while parsing
    '               - RestoreIndex function added, to retrieve the previously stored pointer
    '               - SkipBackTo and SkipBackToExact function added to parse backward 

    '------------------------------------------------------------------------------------------

#Region "----  Private class members"
    '==========================================================================================
    'Private class members
    '==========================================================================================
    Private myIndex As Integer
    Private myStoredIndex As Integer
    Private myAgent As String
    Private myContent As String
    Private myURL As String
    Private myFetchTime As System.DateTime

#End Region

#Region "----  Protected class properties"
    '==========================================================================================
    'Protected class properties
    '==========================================================================================

    '------------------------------------------------------------------------------------------
    Protected ReadOnly Property FetchTime() As System.DateTime
        Get
            Return myFetchTime
        End Get
    End Property

    '------------------------------------------------------------------------------------------
    Protected Property URL() As String
        'URL will be set trough overridden method constructURL
        Get
            Return URL
        End Get
        Set(ByVal Value As String)
            myURL = Value
        End Set
    End Property

    '------------------------------------------------------------------------------------------
    Protected Property Agent() As String
        Get
            Return myAgent
        End Get
        Set(ByVal Value As String)
            myAgent = Value
        End Set
    End Property


#End Region

#Region "----  Overridable class properties"
    '==========================================================================================
    'Overridable class properties
    '==========================================================================================

    '------------------------------------------------------------------------------------------
    Overridable ReadOnly Property Name() As String
        Get
            Return ""
        End Get
    End Property

    '------------------------------------------------------------------------------------------
    Overridable ReadOnly Property Version() As String
        Get
            Return ""
        End Get
    End Property

    '------------------------------------------------------------------------------------------
    Overridable ReadOnly Property Copyright() As String
        Get
            Return ""
        End Get
    End Property

    '------------------------------------------------------------------------------------------
    Overridable ReadOnly Property OtherInformation() As String
        Get
            Return ""
        End Get
    End Property

#End Region

#Region "----  Class methods"
    '==========================================================================================
    'Class methods
    '==========================================================================================

    Public Sub New()
        myIndex = 0
    End Sub

#End Region

#Region "----  Public methods"

    '==========================================================================================
    'Public methods
    '==========================================================================================

    '------------------------------------------------------------------------------------------
    Public Sub FetchResource()
        'reset fetch status
        myContent = ""
        myFetchTime = Now

        Do
            'construct myURL to be fetched
            ConstructURL(myURL)

            'get and parse fetched myContent
            ResetIndex()
            Try
                GetContent(myURL)
            Catch ex As Exception
                Throw New System.Exception("Error fetching myContent", ex)
            End Try

            Try
                ParseContent()
            Catch ex As Exception
                Throw New System.Exception("Error parsing myContent", ex)
            End Try
        Loop Until Not MoreAvailable()
    End Sub

    '------------------------------------------------------------------------------------------
    Public Function URLExists() As Boolean
        'is a bit slow, cause it has to get the whole page from the specified myURL
        'but some webservers respond with a error page if we use a GETHEADER call
        Dim myResponse As WebResponse
        Dim myRequest As WebRequest = HttpWebRequest.Create(myURL)
        Try
            myResponse = myRequest.GetResponse()
        Catch
            Dim ex As Exception
            Return False
        Finally
            myResponse.Close()
        End Try

        Return True
    End Function

#End Region

#Region "----  Overridable methods for derived classes"

    '==========================================================================================
    'Overridable methods for derived classes
    '==========================================================================================

    '------------------------------------------------------------------------------------------
    MustOverride Sub ConstructURL(ByRef myURL As String)

    '------------------------------------------------------------------------------------------
    Overridable Function IsPost() As Boolean
        Return False
    End Function

    '------------------------------------------------------------------------------------------
    Overridable Sub GetPostData(ByRef myPostData As Collections.Specialized.NameValueCollection)
    End Sub

    '------------------------------------------------------------------------------------------
    Overridable Function Init() As Boolean
        Return True
    End Function

    '------------------------------------------------------------------------------------------
    Overridable Function MoreAvailable() As Boolean
        Return False
    End Function

    '------------------------------------------------------------------------------------------
    MustOverride Sub ParseContent()

#End Region

#Region "----  Protected helper methods used by derived class"
    '==========================================================================================
    'Protected helper methods used by derived class
    '==========================================================================================

    '------------------------------------------------------------------------------------------
    Protected Function At(ByVal text As String) As Boolean
        Return FindNoCase(myContent, text, myIndex) = myIndex
    End Function

    '------------------------------------------------------------------------------------------
    Protected Function AtExact(ByVal text As String) As Boolean
        Return myContent.IndexOf(text, myIndex) = myIndex
    End Function

    '------------------------------------------------------------------------------------------
    Protected Function SkipTo(ByVal text As String) As Boolean
        Dim newIndex As Integer = FindNoCase(myContent, text, myIndex)
        If newIndex = -1 Then
            Return False
        End If
        myIndex = newIndex + text.Length
        Return True
    End Function

    '------------------------------------------------------------------------------------------
    Protected Function SkipToExact(ByVal text As String) As Boolean
        Dim newIndex As Integer = myContent.IndexOf(text, myIndex)
        If newIndex = -1 Then
            Return False
        End If
        myIndex = newIndex + text.Length
        Return True
    End Function

    '------------------------------------------------------------------------------------------
    Protected Function SkipBackTo(ByVal text As String) As Boolean
        Dim newIndex As Integer = FindRevNoCase(myContent, text, myIndex)
        If newIndex = -1 Then
            Return False
        End If
        myIndex = newIndex + text.Length
        Return True
    End Function

    '------------------------------------------------------------------------------------------
    Protected Function SkipBackToExact(ByVal text As String) As Boolean
        Dim newIndex As Integer = InStrRev(myContent, text, myIndex, CompareMethod.Text)
        If newIndex = -1 Then
            Return False
        End If
        myIndex = newIndex + text.Length
        Return True
    End Function

    '------------------------------------------------------------------------------------------
    Protected Function ExtractTo(ByVal terminator As String, ByRef result As String) As Boolean
        Dim Length As Integer = myContent.Length
        If myIndex < (Length - 1) Then
            Dim endSegment As Integer = FindNoCase(myContent, terminator, myIndex)
            If endSegment <> -1 Then
                result = Mid(myContent, myIndex + 1, endSegment - myIndex)
                myIndex = endSegment + terminator.Length
                Return True
            End If
        End If
        Return False
    End Function

    '------------------------------------------------------------------------------------------
    Protected Function ExtractToExact(ByVal terminator As String, ByRef result As String) As Boolean
        Dim Length As Integer = myContent.Length
        If myIndex < (Length - 1) Then
            Dim endSegment As Integer = myContent.IndexOf(terminator, myIndex)
            If endSegment <> -1 Then
                result = Mid(myContent, myIndex + 1, endSegment - myIndex)
                myIndex = endSegment + terminator.Length
                Return True
            End If
        End If
        Return False
    End Function

    '------------------------------------------------------------------------------------------
    Protected Sub ExtractToEnd(ByRef result As String)
        Dim Length As Integer = myContent.Length
        If myIndex < (Length - 1) Then
            result = Mid(myContent, myIndex + 1, Length - myIndex)
        End If
    End Sub

    '------------------------------------------------------------------------------------------
    Protected Sub GetLinks(ByRef documents As String(), ByRef images As String())
        'remove comments and script and fix links
        Dim OriginalmyContent As String = myContent
        RemoveComments()
        RemoveScripts()
        myContent = ReplaceEvery(myContent, "'", """")

        'create URL prefix - this will be used to create fully qualified URLs
        Dim myURLPrefix As String = myURL
        Dim Slash As Integer = myURLPrefix.LastIndexOf("/")
        If Slash > 7 Then
            myURLPrefix = Left(myURLPrefix, Slash)
        End If

        'extract HREF targets - prepend base URL if extracted myURL is relative
        Dim baseURL As String
        While SkipTo("href=""")
            If ExtractTo("""", baseURL) Then
                Trim(baseURL)
                If baseURL.IndexOf("mailto:") = -1 Then
                    If baseURL.IndexOf("http://") <> 0 Then
                        If baseURL.Chars(0) = "/" Then
                            baseURL = [String].Format("{0}{1}", myURLPrefix, baseURL)
                        Else
                            baseURL = [String].Format("{0}/{1}", myURLPrefix, baseURL)
                        End If
                    End If
                    If documents Is Nothing Then
                        ReDim Preserve documents(0)
                        documents(0) = baseURL
                    Else
                        If FindStringInArray(documents, baseURL) = -1 Then
                            Dim i As Integer = documents.Length
                            ReDim Preserve documents(i)
                            documents(i) = baseURL
                        End If
                    End If
                End If
            End If
        End While

        'extract SRC targets - prepend base myURL if extracted myURL is relative
        ResetIndex()
        While SkipTo("src=""")
            If ExtractTo("""", baseURL) Then
                Trim(baseURL)
                If baseURL.IndexOf("http://") <> 0 Then
                    If baseURL.Chars(0) = "/" Then
                        baseURL = [String].Format("{0}{1}", myURLPrefix, baseURL)
                    Else
                        baseURL = [String].Format("{0}/{1}", myURLPrefix, baseURL)
                    End If
                End If
                If images Is Nothing Then
                    ReDim Preserve images(0)
                    images(0) = baseURL
                Else
                    If FindStringInArray(images, baseURL) = -1 Then
                        Dim i As Integer = images.Length
                        ReDim Preserve images(i)
                        images(i) = baseURL
                    End If
                End If
            End If
        End While

        'restore original myContent
        myContent = OriginalmyContent
        ResetIndex()
    End Sub

    '------------------------------------------------------------------------------------------
    Protected Sub ResetIndex()
        myIndex = 0
    End Sub

    '------------------------------------------------------------------------------------------
    Protected Sub StoreIndex()
        myStoredIndex = myIndex
    End Sub

    '------------------------------------------------------------------------------------------
    Protected Sub RestoreIndex()
        myIndex = myStoredIndex
    End Sub

    '------------------------------------------------------------------------------------------
    Protected Function OffsetIndex() As Integer
        Return myIndex - myStoredIndex
    End Function

    '------------------------------------------------------------------------------------------
    Protected Function ReplaceEvery(ByVal target As String, ByVal occurence As String, ByVal replacement As String) As String
        Dim lowerTarget As String = target.ToLower
        Dim lowerOccurence As String = occurence.ToLower

        'search the lowercase version, replace in the original version
        Dim pos As Integer = 0
        pos = lowerTarget.IndexOf(lowerOccurence, pos)
        While pos <> -1
            'need for empty "newstr" cases
            lowerTarget.Remove(pos, occurence.Length)
            lowerTarget.Insert(pos, replacement)
            'actually replace
            target.Remove(pos, occurence.Length)
            target.Insert(pos, replacement)
            'ckeck next occurence
            pos += replacement.Length
            pos = lowerTarget.IndexOf(lowerOccurence, pos)
        End While
        Return target
    End Function

    '------------------------------------------------------------------------------------------
    Protected Sub RemoveComments()
        ResetIndex()
        Dim myContentBody As String
        Dim myContentSegment As String
        While ExtractTo("<!--", myContentSegment)
            myContentBody += myContentSegment
            If Not SkipTo("-->") Then
                myContent = myContentBody
                ResetIndex()
                Return
            End If
        End While
        ExtractToEnd(myContentSegment)
        myContentBody += myContentSegment
        'replace existing myContent
        myContent = myContentBody
        ResetIndex()
    End Sub

    '------------------------------------------------------------------------------------------
    Protected Sub RemoveScripts()
        ResetIndex()
        Dim myContentBody As String
        Dim myContentSegment As String
        While ExtractTo("<script", myContentSegment)
            myContentBody += myContentSegment
            If Not SkipTo("/script>") Then
                myContent = myContentBody
                ResetIndex()
                Return
            End If
        End While
        ExtractToEnd(myContentSegment)
        myContentBody += myContentSegment
        'replace existing myContent
        myContent = myContentBody
        ResetIndex()
    End Sub

    '------------------------------------------------------------------------------------------
    Protected Sub RemoveEnclosingAnchorTag(ByRef text As String)
        If text.IndexOf("<a") = 0 Or text.IndexOf("<A") = 0 Then
            Dim newIndex As Integer = text.IndexOf(">")
            If newIndex <> -1 Then
                text = Right(text, text.Length - newIndex - 1)
                newIndex = text.IndexOf("<")
                If newIndex <> -1 Then
                    text = Left(text, newIndex)
                End If
            End If
        End If
    End Sub

    '------------------------------------------------------------------------------------------
    Protected Sub RemoveEnclosingQuotes(ByRef text As String)
        Dim myLength As Integer = text.Length
        If text.Chars(0) = """" And text.Chars(myLength - 1) = """" Then
            text = Mid(text, 2, myLength - 2)
        End If
    End Sub

    '------------------------------------------------------------------------------------------
    Protected Sub RemoveHTML(ByRef text As String)

        'do some common replacements
        ReplaceSpecialChars(text)

        'remove all tags
        Dim cleanText As String = ""
        Dim myIndex As Integer = 0
        Dim startTag As Integer = text.IndexOf("<", myIndex)
        While startTag <> -1
            'extract the start of tag
            Dim subText As String = Mid(text, myIndex + 1, startTag - myIndex)
            cleanText += subText
            myIndex = startTag + 1

            'skip over tag
            Dim endTag As Integer = text.IndexOf(">", myIndex)
            If endTag = -1 Then
                Exit Sub
            End If
            myIndex = endTag + 1
            startTag = text.IndexOf("<", myIndex)
        End While

        'gather remaining text
        If myIndex < text.Length Then
            cleanText += Right(text, text.Length - myIndex)
        End If
        text = cleanText
        cleanText = ""

    End Sub

    '------------------------------------------------------------------------------------------
    Protected Sub ReplaceSpecialChars(ByRef text As String)
        Static Dim myHash As Hashtable
        If myHash Is Nothing Then
            myHash = New Hashtable(100)
            'the first time we have to build the hash table
            With myHash
                .Add("<p>", vbCrLf)
                .Add("&Aacute;", "�")
                .Add("&aacute;", "�")
                .Add("&Acirc;", "�")
                .Add("&acirc;", "�")
                .Add("&acute;", "�")
                .Add("&AElig;", "�")
                .Add("&aelig;", "�")
                .Add("&Agrave;", "�")
                .Add("&agrave;", "�")
                .Add("&amp;", "&")
                .Add("&Aring;", "�")
                .Add("&aring;", "�")
                .Add("&Atilde;", "�")
                .Add("&atilde;", "�")
                .Add("&Auml;", "�")
                .Add("&auml;", "�")
                .Add("&brvbar;", "�")
                .Add("&brkbar;", "�")
                .Add("&Ccedil;", "�")
                .Add("&ccedil;", "�")
                .Add("&cedil;", "�")
                .Add("&cent;", "�")
                .Add("&copy;", "�")
                .Add("&curren;", "�")
                .Add("&deg;", "�")
                .Add("&divide;", "�")
                .Add("&Eacute;", "�")
                .Add("&eacute;", "�")
                .Add("&Ecirc;", "�")
                .Add("&ecirc;", "�")
                .Add("&Egrave;", "�")
                .Add("&egrave;", "�")
                .Add("&ETH;", "�")
                .Add("&eth;", "�")
                .Add("&Euml;", "�")
                .Add("&euml;", "�")
                .Add("&frac12;", "�")
                .Add("&frac14;", "�")
                .Add("&frac34;", "�")
                .Add("&gt;", ">")
                .Add("&Iacute;", "�")
                .Add("&iacute;", "�")
                .Add("&Icirc;", "�")
                .Add("&icirc;", "�")
                .Add("&iexcl;", "�")
                .Add("&Igrave;", "�")
                .Add("&igrave;", "�")
                .Add("&iquest;", "�")
                .Add("&Iuml;", "�")
                .Add("&iuml;", "�")
                .Add("&laquo;", "�")
                .Add("&lt;", "<")
                .Add("&macr;", "�")
                .Add("&hibar;", "�")
                .Add("&micro;", "�")
                .Add("&middot;", "�")
                .Add("&nbsp;", " ")
                .Add("&not", "�")
                .Add("&Ntilde;", "�")
                .Add("&ntilde;", "�")
                .Add("&Oacute;", "�")
                .Add("&oacute;", "�")
                .Add("&Ocirc;", "�")
                .Add("&ocirc;", "�")
                .Add("&Ograve;", "�")
                .Add("&ograve;", "�")
                .Add("&ordf;", "�")
                .Add("&ordm;", "�")
                .Add("&Oslash;", "�")
                .Add("&oslash;", "�")
                .Add("&Otilde;", "�")
                .Add("&otilde;", "�")
                .Add("&Ouml;", "�")
                .Add("&ouml;", "�")
                .Add("&para;", "�")
                .Add("&plusmn;", "�")
                .Add("&pound;", "�")
                .Add("&quot;", """")
                .Add("&raquo;", "�")
                .Add("&reg;", "�")
                .Add("&sect;", "�")
                .Add("&shy;", "�")
                .Add("&sup1;", "�")
                .Add("&sup2;", "�")
                .Add("&sup3;", "�")
                .Add("&szlig;", "�")
                .Add("&THORN;", "�")
                .Add("&thorn;", "�")
                .Add("&times;", "�")
                .Add("&Uacute;", "�")
                .Add("&uacute;", "�")
                .Add("&Ucirc;", "�")
                .Add("&ucirc;", "�")
                .Add("&Ugrave;", "�")
                .Add("&ugrave;", "�")
                .Add("&uml;", "�")
                .Add("&die;", "�")
                .Add("&Uuml;", "�")
                .Add("&uuml;", "�")
                .Add("&Yacute;", "�")
                .Add("&yacute;", "�")
                .Add("&yen;", "�")
                .Add("&yuml;", "�")
            End With
        End If
        Dim myDE As DictionaryEntry
        For Each myDE In myHash
            If text.IndexOf(CStr(myDE.Key)) <> -1 Then
                text = text.Replace(CStr(myDE.Key), CStr(myDE.Value))
            End If
        Next
    End Sub

    '------------------------------------------------------------------------------------------
    Protected Sub Trim(ByRef text As String)
        text = text.Trim()
        text = text.Replace(vbCrLf, " ")
        text = text.Replace(vbCr, " ")
        text = text.Replace(vbLf, " ")
    End Sub

    '------------------------------------------------------------------------------------------
    Sub RemoveWhiteSpace(ByRef text As String)
        Dim RegEx As New RegularExpressions.Regex("\s+")
        text = RegEx.Replace(text, " ")
    End Sub



#End Region

#Region "----  Private helper functions"
    '==========================================================================================
    'Private helper functions
    '==========================================================================================

    Private Function FindNoCase(ByVal text As String, ByVal subText As String, ByVal startIndex As Integer) As Integer
        'get lowercase version of substring
        Dim lcSubText As String = subText.ToLower

        'initialize indices
        Dim textstartIndex As Integer = startIndex
        Dim subtextstartIndex As Integer = 0

        'walk trough string
        While textstartIndex < text.Length
            Dim ch As Char
            ch = ch.ToLower(text.Chars(textstartIndex))
            If subtextstartIndex < lcSubText.Length Then
                If ch = lcSubText.Chars(subtextstartIndex) Then
                    'if source and substring characters match, continue seraching for the rest of the substring
                    textstartIndex += 1
                    subtextstartIndex += 1
                Else
                    'otherwise restart search from the next location in source string
                    startIndex += 1
                    textstartIndex = startIndex
                    subtextstartIndex = 0
                End If
            Else
                'if the entire substring has been found, return its location in the source string
                Return startIndex
            End If
        End While
        'if the search ended because the entire source string segment matched, return the location where the match began
        If subtextstartIndex = lcSubText.Length Then
            Return startIndex
        End If
        'otherwise indicate that the substring wasnt found
        Return -1
    End Function

    '------------------------------------------------------------------------------------------
    Private Function FindRevNoCase(ByVal text As String, ByVal subText As String, ByVal startIndex As Integer) As Integer
        'get lowercase version of substring
        Dim lcSubText As String = subText.ToLower

        'initialize indices
        Dim textstartIndex As Integer = startIndex
        Dim subtextstartIndex As Integer = 0

        'walk trough string
        While textstartIndex < text.Length
            Dim ch As Char
            ch = ch.ToLower(text.Chars(textstartIndex))
            If subtextstartIndex < lcSubText.Length Then
                If ch = lcSubText.Chars(subtextstartIndex) Then
                    'if source and substring characters match, continue seraching for the rest of the substring
                    textstartIndex += 1
                    subtextstartIndex += 1
                Else
                    'otherwise restart search from the next location in source string
                    startIndex -= 1
                    textstartIndex = startIndex
                    subtextstartIndex = 0
                End If
            Else
                'if the entire substring has been found, return its location in the source string
                Return startIndex
            End If
        End While
        'if the search ended because the entire source string segment matched, return the location where the match began
        If subtextstartIndex = lcSubText.Length Then
            Return startIndex
        End If
        'otherwise indicate that the substring wasnt found
        Return -1
    End Function

    '------------------------------------------------------------------------------------------
    Private Function FindStringInArray(ByVal searchArray As String(), ByVal searchText As String) As Integer
        Dim newIndex As Integer = 0
        While newIndex < searchArray.Length
            If [String].Compare(searchText, searchArray(newIndex)) = 0 Then
                Return newIndex
            End If
            newIndex += 1
        End While
        Return -1
    End Function

    '------------------------------------------------------------------------------------------
    Sub GetContent(ByVal url As String)

        Dim myWebClient As WebClient = New WebClient()
        Dim parameterTable As New Collections.Specialized.NameValueCollection()
        Dim responseArray As Byte()

        If IsPost() Then
            GetPostData(parameterTable)
            Try
                responseArray = myWebClient.UploadValues(url, "POST", parameterTable)
            Catch ex As Exception
                Throw New System.Exception("Error reading from website (POST)", ex)
            End Try
        Else
            Try
                responseArray = myWebClient.DownloadData(url)
            Catch ex As Exception
                Throw New System.Exception("Error reading from website (POST)", ex)
            End Try
        End If
        myContent = Encoding.Default.GetString(responseArray)
        myWebClient.Dispose()
    End Sub
#End Region


End Class

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Cello
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Switzerland Switzerland
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