VB.NET

HTTP GET -- Read Response from Stream

Demonstrates how to send an HTTP GET for a web page, and then read the response from a Stream. The purpose is to fulfill a situation such as the following: "I have a URL and just want the <head> </head> portion of the HTML. This would avoid having to download a potentially enormous web page just to get at header information, such as the <styles>."

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Dim success As Boolean = False

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

Dim rest As New Chilkat.Rest

' In this example, we'll get the web page at http://www.nytimes.com/pages/business/index.html
' The domain is "www.nytimes.com", and the path is "/pages/business/index.html"

' If we have only the full URL to begin with, it can be loaded into the Chilkat URL object to
' access the parts:
Dim url As New Chilkat.Url
url.ParseUrl("http://www.nytimes.com/pages/business/index.html")

Dim bAutoReconnect As Boolean = True
success = rest.Connect(url.Host,url.Port,url.Ssl,bAutoReconnect)

' Send the GET request (This sends the GET request, but does not read the response.)
success = rest.SendReqNoBody("GET",url.Path)
If (success <> True) Then
    Debug.WriteLine(rest.LastErrorText)
    Exit Sub
End If


' Read the response header.
Dim responseStatusCode As Integer = rest.ReadResponseHeader()
If (responseStatusCode < 0) Then
    Debug.WriteLine(rest.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Response status code = " & responseStatusCode)

' We expect a 200 response status.
If (responseStatusCode <> 200) Then

    ' If the response status code is not 200, we could check for a redirect status code and 
    ' then follow it, read the entire response (as shown here), or just call rest.Disconnect
    Dim errResponse As String = rest.ReadRespBodyString()
    If (rest.LastMethodSuccess <> True) Then
        Debug.WriteLine(rest.LastErrorText)
    Else
        Debug.WriteLine(errResponse)
    End If


    Exit Sub
End If


Dim bodyStream As New Chilkat.Stream
' Set a 10 second read timeout for the stream. 
' (Give up if no data arrives within 10 seconds after calling a read method.)
bodyStream.ReadTimeoutMs = 10000

' Create a background thread task to read the response body (which feeds
' it to the bodyStream object.)
Dim readResponseBodyTask As Chilkat.Task = rest.ReadRespBodyStreamAsync(bodyStream,True)

' Start the task. 
success = readResponseBodyTask.Run()

' Read the HTTP response body until the "</head>" is seen, or until
' the end-of-stream is reached.

Dim sbBody As New Chilkat.StringBuilder
Dim exitLoop As Boolean = False
While Not exitLoop And (bodyStream.EndOfStream <> True)

    Dim bodyText As String = bodyStream.ReadString()
    If (bodyStream.LastMethodSuccess = True) Then
        sbBody.Append(bodyText)
        If (sbBody.Contains("</head>",False)) Then
            exitLoop = True
        End If

    Else
        exitLoop = True
    End If


End While

' Cancel the remainder of the task...
readResponseBodyTask.Cancel()



' Ensure we're disconnected from the server.
Dim maxWaitMs As Integer = 50
rest.Disconnect(maxWaitMs)

Debug.WriteLine("----")
Debug.WriteLine(sbBody.GetAsString())
Debug.WriteLine("----")
Debug.WriteLine("Successfully received the body up to the desired point.")