How to extract custom header value in Web API mess

Question

I currently have a message handler in my Web API service that overrides 'SendAsync' as follows:

protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
  //implementation
}

Within this code I need to inspect a custom added request header value named MyCustomID. The problem is when I do the following:

if (request.Headers.Contains("MyCustomID"))  //OK
    var id = request.Headers["MyCustomID"];  //build error - not OK

...I get the following error message:

Cannot apply indexing with [] to an expression of type 'System.Net.Http.Headers.HttpRequestHeaders'

How can I access a single custom request header via the HttpRequestMessage (MSDN Documentation) instance passed into this overridden method?

Answer 1

Create a new method - 'Returns an individual HTTP Header value' and call this method with key value everytime when you need to access multiple key Values from HttpRequestMessage.

public static string GetHeader(this HttpRequestMessage request, string key)
        {
            IEnumerable<string> keys = null;
            if (!request.Headers.TryGetValues(key, out keys))
                return null;

            return keys.First();
        }

Answer 2

For ASP.NET you can get the header directly from parameter in controller method using this simple library/package. It provides a [FromHeader] attribute just like you have in ASP.NET Core :). For example:

    ...
    using RazHeaderAttribute.Attributes;

    [Route("api/{controller}")]
    public class RandomController : ApiController 
    {
        ...
        // GET api/random
        [HttpGet]
        public IEnumerable<string> Get([FromHeader("pages")] int page, [FromHeader] string rows)
        {
            // Print in the debug window to be sure our bound stuff are passed :)
            Debug.WriteLine($"Rows {rows}, Page {page}");
            ...
        }
    }

Answer 3

Try something like this:

IEnumerable<string> headerValues = request.Headers.GetValues("MyCustomID");
var id = headerValues.FirstOrDefault();

There's also a TryGetValues method on Headers you can use if you're not always guaranteed to have access to the header.

Answer 4

One line solution

var id = request.Headers.GetValues("MyCustomID").FirstOrDefault();

Answer 5

For ASP.Net Core there is an easy solution if want to use the param directly in the controller method: Use the [FromHeader] annotation.

        public JsonResult SendAsync([FromHeader] string myParam)
        {
        if(myParam == null)  //Param not set in request header
        {
           return null;
        }
        return doSomething();
    }   

Additional Info: In my case the "myParam" had to be a string, int was always 0.

Answer 6

request.Headers.FirstOrDefault( x => x.Key == "MyCustomID" ).Value?.FirstOrDefault()

modern variant :)