如何接受ISO格式的WebAPI TimeSpan参数

Question

I recently built a service with Web API and there's an API which needs to accept a TimeSpan parameter in ISO 8601 format (eg PT5M ).

Here's my api controller:

[RoutePrefix("api")]
public class StatisticsController : ApiController
{
    [Route("statistics")]
    public async Task<IEnumerable<StatPoint>> GetStatistics([FromUri] TimeSpan duration)
    {
        // ...
    }
}

And I need to access this API with url like /api/statistics?duration=PT5M .

I tried to add a JsonConverter as some people said online:

public class IsoTimeSpanConverter : JsonConverter
{
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var ts = (TimeSpan) value;
        var tsString = XmlConvert.ToString(ts);
        serializer.Serialize(writer, tsString);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue,
        JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
        {
            return null;
        }

        var value = serializer.Deserialize<String>(reader);
        return XmlConvert.ToTimeSpan(value);
    }

    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof (TimeSpan) || objectType == typeof (TimeSpan?);
    }
}

And in GlobalConfiguration.Configure (called in Application_start() ):

config.Formatters.JsonFormatter.SerializerSettings.Converters.Add(new IsoTimeSpanConverter());

However it did not work, I always get this error message:

{
    message: "The request is invalid.",
    messageDetail: "The parameters dictionary contains a null entry for parameter 'duration' of non-nullable type 'System.TimeSpan' for method 'System.Threading.Tasks.Task`1[System.Collections.Generic.IEnumerable`1[WebRole.Api.Models.StatPoint]] GetStatistics(System.TimeSpan)' in 'WebRole.Api.StatisticsController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter."
}

Any help is appreciated.

Answer 1

I guess I found the solution. I was on the wrong way since JsonConverter handles the body serialization, while the parsing of URL parameter is handled by ModelBinder . These are two different mechanisms.

I read this article and created the following ModelBinder:

public class IsoTimeSpanModelBinder: IModelBinder
{
    public bool BindModel(HttpActionContext actionContext, ModelBindingContext bindingContext)
    {
        if(bindingContext.ModelType != typeof(TimeSpan))
        {
            return false;
        }

        var val = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
        if(val == null)
        {
            return false;
        }

        var key = val.RawValue as string;
        if(key == null)
        {
            bindingContext.ModelState.AddModelError(bindingContext.ModelName, "Wrong value type for TimeSpan");
            return false;
        }

        try
        {
            bindingContext.Model = XmlConvert.ToTimeSpan(key);
            return true;
        }
        catch (Exception e)
        {
            bindingContext.ModelState.AddModelError(
                bindingContext.ModelName, "Cannot convert value to TimeSpan: " + e.Message);
            return false;
        }
    }
}

Then config to use it to parse all TimeSpan :

public class Global : System.Web.HttpApplication
{
    protected void Application_Start(object sender, EventArgs e)
    {
        GlobalConfiguration.Configure(Register);
    }

    public static void Register(HttpConfiguration config)
    {
        // Parse TimeSpan in ISO format (e.g. PT5M)
        config.Services.Insert(
            typeof(ModelBinderProvider), 0,
            new SimpleModelBinderProvider(typeof(TimeSpan), new IsoTimeSpanModelBinder()));
    }
}

It is also possible to parse any user-defined type in custom formats. Very flexible!

Answer 2

Give a try to this in Application_start()

var formatters = GlobalConfiguration.Configuration.Formatters;
var jsonFormatter = formatters.JsonFormatter;
jsonFormatter.SerializerSettings.Converters.Add(new IsoTimeSpanConverter());

Update:

Is there any reason you are taking parameter as TimeSpan in function?

You can take string duration and then start your function with

        try
        {
            TimeSpan tt = XmlConvert.ToTimeSpan(duration);
        }
        catch(Exception ex)
        {

        }

as your custom code is doing the same converting a string (ISO Time) to timespan.