How to add more parameters to a JSON WebService without breaking call from old clients?

Question

I want to add more parameters to my JSON WebService without breaking call from old clients. Example:

My WebService in Service.asmx

[WebMethod]
public string Ping(string msg, string additionalInfo)
{
    if (string.IsNullOrEmpty(additionalInfo))
    {
        return "Process msg with old version";
    }
    return "Process msg with new version"; ;
}

//My old web service does not have additionalInfo arguments
//public string Ping(string msg) {..}

Web.config tells that my WebService is JSON-based

<system.web.extensions>
  <scripting>
       <webServices>
           <jsonSerialization maxJsonLength="50000000" />
       </webServices>
   </scripting>

if clients call my new Json WebService with all the parameters => everything is fine

CallWs("http://localhost:48918/Service.asmx/Ping", '{"msg":"hello", "additionalInfo":""}')

But all the current clients won't give the additionalInfo:

CallWs("http://localhost:48918/Service.asmx/Ping", '{"msg":"hello"}')

my new WebService will immediately return error:

string(654) "{"Message":"Invalid web service call, missing value for parameter: \u0027additionalInfo\u0027.","StackTrace":"   at System.Web.Script.Services.WebServiceMethodData.CallMethod(Object target, IDictionary`2 parameters)\r\n   at System.Web.Script.Services.WebServiceMethodData.CallMethodFromRawParams(Object target, IDictionary`2 parameters)\r\n   at System.Web.Script.Services.RestHandler.InvokeMethod(HttpContext context, WebServiceMethodData methodData, IDictionary`2 rawParams)\r\n   at System.Web.Script.Services.RestHandler.ExecuteWebServiceCall(HttpContext context, WebServiceMethodData methodData)","ExceptionType":"System.InvalidOperationException"}"

So my customers will have to change theire code in order to use my new WebService, I don't want that. I want to give default values to my new WebService, What is the best way to do?

Possible duplication: Can I have an optional parameter for an ASP.NET SOAP web service But none of the response works for me.

---

FYI my customers often call my JSON WebService via PHP, they simply make a POST request to the service endpoint:

$ch = curl_init("http://localhost:48918/Service.asmx/Ping");
$wsrq = array(
    "msg" => "Hello",
    //"additionalInfo" => "World",
);
curl_setopt_array($ch, array(
    CURLOPT_POST => TRUE,
    CURLOPT_RETURNTRANSFER => TRUE,
    CURLOPT_SSL_VERIFYPEER => FALSE,
    CURLOPT_POSTFIELDS => json_encode($wsrq),
    CURLOPT_HTTPHEADER => array("Content-type: application/json; charset=utf-8"),
));
$response = curl_exec($ch);

Answer 1

It looks like the proper way to achieve that is to use method overloads for your service methods. Also for the future methods I would recommend you using models:

public class MyModel
{
    public string Message { get; set; }
    public string AdditionalInfo { get; set; }
}

and then:

[WebMethod]
public string Ping(MyModel model)
{
    ...
}

This will give you more flexibility because you will be able to add properties easily in the future without breaking.

This being said, there's one approach or a workaround that you might consider: manual deserialization (I totally don't recommend it but worth mentioning).

Make your WebMethod without any parameters:

[WebMethod]
public string Ping()

and then read the request body manually by accessing the input stream:

[WebMethod]
public string Ping()
{
    Context.Request.InputStream.Seek(0, SeekOrigin.Begin);
    using (var inputStream = Context.Request.InputStream)
    using (var reader = new StreamReader(inputStream))
    {
        string body = reader.ReadToEnd();

        // TODO: Worth checking the request headers before attempting JSON deserialization
        // For example the Content-Type header
        var model = JsonConvert.DeserializeObject<MyModel>(body);
        if (string.IsNullOrEmpty(model.AdditionalInfo))
        {
            return "Process msg with old version";
        }
        return "Process msg with new version"; ;
    }
}

To avoid mixing multiple responsibilities in your service method you could move the parsing of the body stream into some separate extension method:

public static class RequestExtensions
{
    public static T ParseRequest<T>(this HttpRequest request)
    {
        request.InputStream.Seek(0, SeekOrigin.Begin);
        using (var inputStream = request.InputStream)
        using (var reader = new StreamReader(inputStream))
        {
            string body = reader.ReadToEnd();
            return JsonConvert.DeserializeObject<T>(body);
        }
    }
}

and then your WebMethod:

[WebMethod]
public string Ping()
{
    var model = Context.Request.ParseRequest<MyModel>();
    if (string.IsNullOrEmpty(model.AdditionalInfo))
    {
        return "Process msg with old version";
    }
    return "Process msg with new version"; ;
}

Now clients can call the Ping method like that:

POST /WebService1.asmx/Ping HTTP/1.1
Content-type: application/json; charset=utf-8
Host: localhost:14529
Content-Length: 61

{
    "msg": "Hello",
    "additionalInfo": "add info"
}

or the old way:

POST /WebService1.asmx/Ping HTTP/1.1
Content-type: application/json; charset=utf-8
Host: localhost:14529
Content-Length: 26

{
    "msg": "Hello"
}