# HTTP Responses & Status Codes

## Check http request format from frontend-basics

# ASP.NET Status Codes

* There are multiple possible status codes for each action
* The ControllerBase which the controllers should inherit from includes  __result methods__  for creating ActionResult objects
  * All ActionResult objects implement IActionResult
  * Includes at least a status code, and can contain data such as view items or an error message
  * This result is processed into a response to then send to client

# ASP.NET Result Methods

| __Status Code__ | __Result Method__ | __Use__ |
| :-: | :-: | :-: |
| __200 - OK__ | __Ok()_ | __GET, DELETE__ |
| __201 - Created__ | __Created()_ | __POST__ |
| __204 - No content__ | __NoContent()_ | __PUT, PATCH__ |
| __400 - Bad request__ | __BadRequest()_ | __POST, PUT, PATCH__ |
| __404 - Not found__ | __NotFound()_ | __All actions__ |
| __Custom__ | __StatusCode()_ | __All actions__ |

# ASP.NET Status Codes (continued)

[HttpGet("{id}")]

public IActionResult GetContactById(int id)

{

// Contacts = list of contact objects, fetched from some repository

var contact = Contacts.FirstOrDefault(c => c.Id == id);

if (contact == null)

{

return NotFound();

}

return Ok(contact);

}

The previous code first attempts to find a Contacts object using the ID provided in the URI parameter

If an item is not found, a 404 response is returned using NotFound()

Otherwise, the object is sent as a payload with a 200 OK code response using Ok(contact)

![](imgs/3-http-responses-and-status-codes_0.png)

![](imgs/3-http-responses-and-status-codes_1.png)

![](imgs/3-http-responses-and-status-codes_2.png)

![](imgs/3-http-responses-and-status-codes_3.png)

# Exercise 1: Returning Status Codes

Without using parameter constraints, modify your number list method from Lecture 2, Exercise 2 to return a status code 400 (Bad Request) if  _k_  is smaller than one or larger than 100.

Add a helpful error message to the result for both cases. The message should be seen as a message body in the response.

Test with Swagger/Postman.