headers3.cs

// the attribute itself - to put against our action parameters.
// combines the model binding engine with our value provider factory.
public class FromHeaderAttribute : ParameterBindingAttribute
{
    public override HttpParameterBinding GetBinding(HttpParameterDescriptor parameter)
    {
        var httpConfig = parameter.Configuration;
        var binder = new ModelBinderAttribute()
            .GetModelBinder(httpConfig, parameter.ParameterType);
        return new ModelBinderParameterBinding(
            parameter, binder,
            new ValueProviderFactory[] { new HeaderValueProviderFactory() });
    }
}

// factory for creating our custom value provider class given a specific action
// context. this is where we capture and keep reference to the HTTP headers
// for the request .
public class HeaderValueProviderFactory : ValueProviderFactory
{
    public override IValueProvider GetValueProvider(HttpActionContext actionContext)
    {
        return new HeaderValueProvider(actionContext.Request.Headers);
    }
}

// Our value provider, which handles the bulk of the work
public class HeaderValueProvider : IValueProvider
{
    private readonly HttpRequestHeaders _headers;

    public HeaderValueProvider(HttpRequestHeaders headers)
    {
        _headers = headers;
    }

    public bool ContainsPrefix(string prefix)
    {
        // all prefixes are flattened - all members and sub-members
        // considered equally
        return true;
    }

    // the heart of the approach. this will be called for each property of the
    // model we’re binding to – we need only find and return the appropriate
    // values
    public ValueProviderResult GetValue(string key)
    {
        IEnumerable values;

        var propName = RemovePrefixes(key);
        var headerName = MakeHeaderName(propName);

        if (!_headers.TryGetValues(headerName, out values))
        {
            return null;
        }

        var data = string.Join(",", values.ToArray());
        return new ValueProviderResult(values, data, CultureInfo.InvariantCulture);
    }

    private static string RemovePrefixes(string key)
    {
        var lastDot = key.LastIndexOf('.');
        if (lastDot == -1) return key;

        return key.Substring(lastDot + 1);
    }

    // here’s the simple algorithm for making a HTTP header name out of our members:
    // iterate through the characters, inserting a dash before uppercase letters,
    // with the exception of the first character
    private static string MakeHeaderName(string key)
    {
        var headerBuilder = new StringBuilder();

        for (int i = 0; i < key.Length; i++)
        {
            if (char.IsUpper(key[i]) && i > 0)
            {
                headerBuilder.Append('-');
            }
            headerBuilder.Append(key[i]);
        }

        return headerBuilder.ToString();
    }
}