I was working on creating a .NET Core-based API and came across a requirement to read a particular request header across the API controllers. To understand it better, let us say there are two API controllers,
- InvoiceController
- ProductController
We need to read the value of a particular Request Header in both controllers.
To do that, add a middleware class; I am naming it RequestCodeMiddleware, as we will read a request header named- “Request-Code.”
public class RequestCodeMiddleware
{
private readonly RequestDelegate _next;
public RequestCodeMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task Invoke(HttpContext context)
{
// Read the request code here. This is just an example, replace it with your actual logic.
var requestCode = context.Request.Headers["Request-Code"].FirstOrDefault();
// Add the request code to the HttpContext
context.Items["RequestCode"] = requestCode+"middle ware";
// what is stopping us to read client id
// will that be a good practice ?
// Call the next middleware in the pipeline
await _next(context);
}
}
After creating the middleware class, register it to the API handling pipeline by adding the below code,
if (app.Environment.IsDevelopment())
{
app.UseSwagger();
app.UseSwaggerUI();
}
app.UseMiddleware<RequestCodeMiddleware>();
app.UseHttpsRedirection();
app.MapControllers();
app.Run();
Now, you can read the request header in a ProductController’s GET Action, as shown below.
public class product : ControllerBase
{
[HttpGet]
public string Get()
{
var requestCode = HttpContext.Items["RequestCode"] as string;
return requestCode;
}
}
So far, so good; however, there is still a challenge: the above code must be duplicated to read the request header in the multiple Actions. To avoid that, we can read it inside the controller’s constructor; however, HttpContext is unavailable inside a controller’s constructor.
Another approach is to use IHttpContextAccesor.
To use IHttpContextAccesor, register it in the API startup pipeline as shown below,
builder.Services.AddHttpContextAccessor();
Now in the constructor of the InvoiceController, you can inject IHttpContextAccesor to read the request header as shown in the below code listing.
public class invoice : ControllerBase
{
private readonly IHttpContextAccessor _httpContextAccessor;
private string _requestCode;
public invoice(IHttpContextAccessor httpContextAccessor)
{
_httpContextAccessor = httpContextAccessor;
_requestCode = _httpContextAccessor.HttpContext.Items["RequestCode"] as string;
}
// Your action methods..
// GET: api/<invoice>
[HttpGet]
public string Get()
{
return _requestCode;
}
}
In this way, we can read a request header in multiple controllers. I hope you find this post helpful. Thanks for reading.
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Dhananjay Kumar 