(VB.NET) REST Follow Redirects

Demonstrates how to follow a 302/303 redirect response.

Chilkat .NET Downloads Chilkat .NET Framework Chilkat for .NET Core

' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim rest As New Chilkat.Rest

Dim bTls As Boolean = True
Dim port As Integer = 443
Dim bAutoReconnect As Boolean = True
Dim success As Boolean = rest.Connect("chilkatsoft.com",port,bTls,bAutoReconnect)
If (success <> True) Then
    Debug.WriteLine(rest.LastErrorText)
    Exit Sub
End If


' Send a POST to a URL that will respond with a 302 redirect..
rest.AddQueryParam("firstName","John")
rest.AddQueryParam("lastName","Doe")
Dim responseText As String = rest.FullRequestFormUrlEncoded("POST","/echoPost302.asp")
If (rest.LastMethodSuccess <> True) Then
    Debug.WriteLine(rest.LastErrorText)
    Exit Sub
End If


Dim statusCode As Integer = rest.ResponseStatusCode

' Examine the response status code
If (statusCode < 300) Then
    Debug.WriteLine("Not a redirect.")
    Debug.WriteLine(responseText)
    Exit Sub
End If


If (statusCode > 399) Then
    Debug.WriteLine("Error response: Status code = " & statusCode)
    Debug.WriteLine(responseText)
    Exit Sub
End If


Debug.WriteLine("Redirect status code = " & statusCode)

' The response header will contain a Location field with the redirect URL, such as this:
' Location: http://www.chilkatsoft.com/echoPostFinal.asp


' The response status code determines how the client should behave.
' Here are some common possibilities:

' 301: Moved Permanently
' This and all future requests should be directed to the given URI.  (Keep the original HTTP method for the redirect.  In this case, the 
' original request was a POST, so we POST to the redirect URL.)

' 302: Found (aka Object Moved aka Moved Temporarily)
' This is the most popular redirect code, but also an example of industrial practice contradicting the standard. HTTP/1.0 specification (RFC 1945 ) required the client
' to perform a temporary redirect (the original describing phrase was Moved Temporarily), but popular browsers implemented it as a 303 See Other. Therefore, HTTP/1.1
' added status codes 303 and 307 to disambiguate between the two behaviors. However, the majority of Web applications and frameworks still use the 302 status code
' as if it were the 303.

' 303: See Other
' The response to the request can be found under another URI using a GET method. When received in response to a PUT, it should be assumed that the server has
' received the data and the redirect should be issued with a separate GET message.

' 307: Temporary Redirect
' In this occasion, the request should be repeated with another URI, but future requests can still use the original URI. In contrast to 303, the request method
' should not be changed when reissuing the original request. For instance, a POST request must be repeated using another POST request.

Debug.WriteLine(rest.ResponseHeader)

Dim redirectUrl As Chilkat.Url = rest.RedirectUrl()
If (rest.LastMethodSuccess = False) Then
    Debug.WriteLine("No Location header found for redirect.")
    Exit Sub
End If


' Prep for the redirect..
rest.ClearAllParts()

' Disconnect and re-connect.  
' (This can be skipped if both the host and SSL/TLS conditions are the same.)
rest.Disconnect(100)
success = rest.Connect(redirectUrl.Host,redirectUrl.Port,redirectUrl.Ssl,bAutoReconnect)
If (success <> True) Then
    Debug.WriteLine(rest.LastErrorText)
    Exit Sub
End If


If ((statusCode = 301) Or (statusCode = 307)) Then
    ' Redirect using a POST, sending the same params to the new destination
    rest.AddQueryParam("firstName","John")
    rest.AddQueryParam("lastName","Doe")
    responseText = rest.FullRequestFormUrlEncoded("POST",redirectUrl.Path)
    If (rest.LastMethodSuccess <> True) Then
        Debug.WriteLine(rest.LastErrorText)
        Exit Sub
    End If

End If


If ((statusCode = 302) Or (statusCode = 303)) Then
    ' Redirect using a GET, sending the query params found in the redirect URL.
    responseText = rest.FullRequestFormUrlEncoded("GET",redirectUrl.PathWithQueryParams)
    If (rest.LastMethodSuccess <> True) Then
        Debug.WriteLine(rest.LastErrorText)
        Exit Sub
    End If

End If


' Show the final status code and the response text.
Debug.WriteLine("Final status code = " & rest.ResponseStatusCode)

Debug.WriteLine("Final response text (HTML, XML, JSON, or whatever..)")
Debug.WriteLine(responseText)