Making raw web service calls with the HttpWebRequest class

Sometimes it's really nice to be able to make a raw call to a web service by manaully putting together your own SOAP envelope. The System.Net.HttpWebRequest class makes it really easy. There are a number of good reasons to do this. Maybe you want to call a web service without having to create a proxy class with wsdl.exe, or maybe you want to have more control over the creation of the SOAP envelope or you don't want to have to rely on the XmlSerializer. Maybe you want to create the xml by doing xslt transforms rather than serializing a .net type. First you need to create the envelope xml, this function takes a string of xml data as the content and inserts it into a soap envelope. Just open your web service in IE by typing the url into the Address bar to see what the structure of the soap:Body should be.

    static string _soapEnvelope =
@"    xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
    xmlns:xsd='http://www.w3.org/2001/XMLSchema'
    xmlns:soap='http://schemas.xmlsoap.org/soap/envelope/'>
";

    private static XmlDocument CreateSoapEnvelope(string content)
    {
        StringBuilder sb = new StringBuilder(_soapEnvelope);
        sb.Insert(sb.ToString().IndexOf(""), content);

        // create an empty soap envelope
        XmlDocument soapEnvelopeXml = new XmlDocument();
        soapEnvelopeXml.LoadXml(sb.ToString());

        return soapEnvelopeXml;
    }

Next you create the HttpWebRequest object. The url is the url of the .aspx file and the action is your namespace plus the web method, e.g: 'mikehadlow.com/adder'.

    private static HttpWebRequest CreateWebRequest(string url, string action)
    {
        HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);
        webRequest.Headers.Add("SOAPAction", action);
        webRequest.ContentType = "text/xml;charset=/"utf-8/"";
        webRequest.Accept = "text/xml";
        webRequest.Method = "POST";
        return webRequest;
    }

Insert the envelope into the web request.

    private static void InsertSoapEnvelopeIntoWebRequest(XmlDocument soapEnvelopeXml, HttpWebRequest webRequest)
    {
        using (Stream stream = webRequest.GetRequestStream())
        {
            soapEnvelopeXml.Save(stream);
        }
    }

Then you can call .GetResponse on the HttpWebRequest object to call the web service. You get the response back by getting the response stream with the GetResponseStream method of the webResponse object. Here's it all put together:

    static string _url = "http://mikehadlow.com/myService.asmx";
    static string _action = "http://mikehadlow.com/myWebMethod";
    static string _inputPath = @"C:/mike/Play/input.xml";
    static string _outputPath = @"C:/mike/Play/output.xml";

    static void Main(string[] args)
    {
        string content = File.ReadAllText(_inputPath);
        XmlDocument soapEnvelopeXml = CreateSoapEnvelope(content);
        HttpWebRequest webRequest = CreateWebRequest(_url, _action);
        InsertSoapEnvelopeIntoWebRequest(soapEnvelopeXml, webRequest);

        // begin async call to web request.
        IAsyncResult asyncResult = webRequest.BeginGetResponse(null, null);

        // suspend this thread until call is complete. You might want to
        // do something usefull here like update your UI.
        asyncResult.AsyncWaitHandle.WaitOne();

        // get the response from the completed web request.
        string soapResult;
        using (WebResponse webResponse = webRequest.EndGetResponse(asyncResult))
        using (StreamReader rd = new StreamReader(webResponse.GetResponseStream()))
        {
            soapResult = rd.ReadToEnd();
        }
        File.WriteAllText(_outputPath, FormatDocument(soapResult));
    }

Posted by Mike Hadlow at 8:21 PM