How do I form complete URLs from incomplete URLs found in a web page?

Question

I can retrieve the text of a web page, let's say https://stackoverflow.com/questions with some real and made up links:

    /questions
    /tags
    /questions?sort=votes
    /questions?sort=active
    randompage.aspx
    ../coolhomepage.aspx

Knowing my originating page was https://stackoverflow.com/questions is there a way in .Net to resolve the links to this?

    https://stackoverflow.com/questions
    https://stackoverflow.com/tags
    https://stackoverflow.com/questions?sort=votes
    https://stackoverflow.com/questions?sort=active
    https://stackoverflow.com/questions/randompage.aspx
    https://stackoverflow.com/coolhomepage.aspx

Kind of like the way a Browser is smart enough to resolve the links.

=========================== Update - Using David's solution:

    'Regex to match all <a ... /a> links
    Dim myRegEx As New Regex("\<\s*a                   (?# Find opening <a tag)           " & _
                             ".+?href\s*=\s*['""]      (?# Then all to href=' or "" )     " & _
                             "(?<href>.*?)['""]        (?# Then all to the next ' or "" ) " & _
                             ".*?\>                    (?# Then all to > )                " & _
                             "(?<name>.*?)\<\s*/a\s*\> (?# Then all to </a> )             ", _
                             RegexOptions.IgnoreCase Or _
                             RegexOptions.IgnorePatternWhitespace Or _
                             RegexOptions.Multiline)

    'MatchCollection to hold all the links that are matched
    Dim myMatchCollection As MatchCollection
    myMatchCollection = myRegEx.Matches(Me._RawPageText)

    'Loop through all matches and evaluate the value of the href attribute.
    For i As Integer = 0 To myMatchCollection.Count - 1
        Dim thisLink As String = ""
        thisLink = myMatchCollection(i).Groups("href").Value()
        'This checks for Javascript and Mailto links.
        'This is not complete. There are others to check I just haven't encountered them yet.
        If thisLink.ToLower.StartsWith("javascript") Then
            thisLink = "JAVASCRIPT: " & thisLink
        ElseIf thisLink.ToLower.StartsWith("mailto") Then
            thisLink = "MAILTO: " & thisLink
        Else
            Dim baseUri As New Uri(Me.URL)

            If Not thisLink.ToLower.StartsWith("http") Then
                'This is a partial URL so we will assume that it's relative to our originating URL
                Dim myUri As New Uri(baseUri, thisLink)
                thisLink = "RELATIVE LOCAL LINK: RESOLVED: " & myUri.ToString() & " ORIGINAL: " & thisLink
            Else
                'The link starts with HTTP, determine if part of base host or is outside host.
                Dim ThisUri As New Uri(thisLink)
                If ThisUri.Host.ToLower = baseUri.Host.ToLower Then
                    thisLink = "INSIDE COMPLETE LINK: " & thisLink
                Else
                    thisLink = "OUTSIDE LINK: " & thisLink
                End If
            End If

        End If

        'I'm storing the found links into a Generic.List(Of String)
        'This link has descriptive text added to it.
        'TODO: Make collection to hold only unique internal links.
        Me._Links.Add(thisLink)
    Next

Answer 1

You mean like this?

Uri baseUri = new Uri("http://www.contoso.com");
Uri myUri = new Uri(baseUri, "catalog/shownew.htm");

Console.WriteLine(myUri.ToString());

Sample comes from http://msdn.microsoft.com/en-us/library/9hst1w91.aspx

Answer 2

If you mean server-side, you can use ResolveUrl():

string url = ResolveUrl("~/questions");

Answer 3

I dont understand what you mean by "resolve" in this context, but you can try inserting a base html element. Since you asked how the browser would handle it.

"The <base> tag specifies a default address or a default target for all links on a page."

http://www.w3schools.com/TAGS/tag_base.asp