how to post a form use HTTP librarys

Discussion in 'Questions (Windows Mobile)' started by nsc, Jun 9, 2009.

  1. nsc

    nsc New Member

    this form use Image Verification
    need some code samples.
    * bin is Binary file library , bit is Bitwise , obj is Object

    Sub Globals
    'Declare the global variables here.
       Dim buffer(0As Byte
    End Sub

    Sub App_Start
    End Sub

    Sub Button1_Click
    "Post gogogo"
       Request.Method = 
       Request.ContentType = 
       Request.Timeout = 
    "username=nsc&password=XXX&useCookie=1&signonForwardAction=&validcode=" & textbox2.Text
       buffer() = 
       Response.Value = Request.GetResponse
       textbox1.Text = Response.GetString
    End Sub

    Sub Button2_Click
        Response.Value = Request.GetResponse
    0,Response.GetStream) '
        obj.CreateNew2("System.Drawing.Bitmap" & obj.System_Drawing,args.Value)
        image1.Image = obj.Value
    End Sub
    run it , button2 click , it's works , I got a validcode image
    but button1 click , I got error , The remote server returned an error (417) Expectation Failed
    Last edited: Jun 9, 2009
  2. nsc

    nsc New Member

    lighttpd, .NET, HttpWebRequest

    Yesterday, when I deployed the server for my PocketPC-Application to an environment running lighttpd and PHP with FastCGI SAPI, I found out that the communication between the device and the server didn’t work.

    All I got on the client was an Exception because the server sent back error 417: Precondition failed.

    Of course there was nothing in lighttpd’s error log, which made this a job for EtherealWireshark.

    The response from the server had no body explaining what was going on, but in the request-header, something interesting was going on:

    Expect: 100-continue

    Additionally, the request body was empty.

    It looks like HttpWebRequest, with the help of the compact framework’s ServicePointManager is doing something really intelligent which lighttpd doesn’t support:

    By first sending the POST request with an empty body and that Expect: 100-continue-header, HttpWebRequest basically gives the server the chance to do some checks based on the request header (like: Is the client authorized to access the URL? Is there a resource available at that URL?) without the client having to transmit the whole request body first (which can be quite big).

    The idea is that the server does the checks based on the header and then either sends a error response (like 401, 403 or 404) or it advises the client to go ahead and send the request body (code 100).

    Lighttpd doesn’t support this, so it sends that 417 error back.

    The fix is to set Expect100Continue of System.Net.ServicePointManager to false before getting a HttpWebRequest instance.

    That way, the .NET Framework goes back to plain old POST and sends the complete request body.

    In my case that’s no big disadvantage because if the server is actually reachable, the requested URL is guaranteed to be there and ready to accept the data on HTTP-level (of course there may be some errors on the application level, but there has to be a request body for them to be detected).

    This entry was posted on Wednesday, September 13th, 2006 at 10:43 and is filed under Programming, Solutions. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
    3 Responses to “lighttpd, .NET, HttpWebRequest”

    1. Steve Greenland Says:
    October 21st, 2006 at 19:11

    Thanks for this post — I’d figured out the 100-Continue problem with lighttpd (it is a documented bug, but hard to fix with the current code. I’d guess that the 1.5 re-do might fix this, or at least make it possible.) What I’d not been able to find was the magic knob in .NET (or rather, Mono) to bypass the Expect: header. So, again, thanks.

    It’s worth noting that not using the request header should *never* break anything - the server is still allowed to reject the POST for any reason. All the request header does is allow the optimization of not sending the POST body until the basic request has been checked.

    HttpWebRequest request = (HttpWebRequest) WebRequest.Create(uri);
    request.ServicePoint.Expect100Continue = 
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