Introduction

Invoking a Web Service dynamically is not a new topic. I have been using the following method to invoke a web service without a proxy till recently. Later below, you can see a better way of doing this.

Create your SOAP envelope and contents. You will be playing with some strings for a while.

The Conventional Method

// Create and furnish the basic requestor
HttpWebRequest oHttpWebRequest = (HttpWebRequest) WebRequest.Create(URL);
oHttpWebRequest.UseDefaultCredentials = true;
oHttpWebRequest.ContentType = "text/xml";
oHttpWebRequest.Method = "POST";
oHttpWebRequest.Accept = "text/xml";
oHttpWebRequest.Headers.Add("SOAPAction:" + SoapAction);
oHttpWebRequest.UserAgent = "Mozilla/4.0+";
// Encode and post the request
byte[] bytes = System.Text.Encoding.UTF8.GetBytes(sSoapMessage);
Stream oSendStream = oHttpWebRequest.GetRequestStream();
oSendStream.Write(bytes, 0, bytes.Length);
oSendStream.Close();
// Get the response
oHttpResponse = (HttpWebResponse) oHttpWebRequest.GetResponse();
Stream oReceiveStream = oHttpResponse.GetResponseStream();
// Manipulate the stream and extract data here
oHttpResponse.Close();
oReadStream.Close();

I have omitted many plumbing statements here as this is intended only to give a basic idea about how difficult this is.

A Different Approach

The next method also technically works the same way, because there is only one way a SOAP request can be made. The only difference is that the new approach wraps the whole string manipulation inside itself and does all the plumbing work for us. The basic idea is to generate a proxy assembly when you need it as a one time activity.

Uri uri = new Uri(_mUrl); // Create the uri object
WebRequest webRequest = WebRequest.Create(uri);

// Supply credentials, if required
Authenticate(webRequest);

WebResponse webResponse = webRequest.GetResponse();
Stream requestStream = webResponse.GetResponseStream();
// Get a WSDL file describing a service
ServiceDescription serviceDescription = ServiceDescription.Read(requestStream);
// Initialize a service description importer
ServiceDescriptionImporter descriptionImporter = new ServiceDescriptionImporter();
descriptionImporter.AddServiceDescription(serviceDescription, String.Empty, String.Empty);

//The allowed values of this property are:  "Soap", 
//"Soap12", "HttpPost" ,"HttpGet" and "HttpSoap".
//The default value is "Soap", 
//which indicates the SOAP 1.1 standard. This is case sensitive.
descriptionImporter.ProtocolName = "Soap";
descriptionImporter.CodeGenerationOptions = CodeGenerationOptions.GenerateProperties;
CodeNamespace codeNamespace = new CodeNamespace();

// Compile to assembly
compilerResults = codeProvider.CompileAssemblyFromDom(compilerParameters, codeCompileUnit);
Assembly assembly = compilerResults.CompiledAssembly;

// We have a valid assembly now. Try to get the Type from it.
Type type = assembly.GetType(_mTypeName) ?? FindTypeByName(assembly);

// Create the object instance
_mTargetInstance = assembly.CreateInstance(_mTypeName);
// Get the method info object
_mMethodInfo = type.GetMethod(
_mMethodName,
BindingFlags.Public | BindingFlags.IgnoreCase | BindingFlags.IgnoreReturn);

// Invoke the method with necessary arguments
object result = _mMethodInfo.Invoke(_mTargetInstance, parameters);

The advantage in this approach is that you need to execute this whole thing only once when you find the MethodInfo object as null (for the first time). The rest of the time, this will behave just like a normal web service invoke using the conventional method.

I know you might be thinking why should you do like this? Why can’t I invoke like the old way? Well, the answer is ‘it depends’. There are some situations where you decide to post a piece of data to a web service whose URL, method and parameters are known only at run-time, probably from a database configuration or a config file. I found this very useful for my application integration project.

Enjoy coding and let me know if you need help with this.

[C#] Dynamic Web Service Invoker