# HTTP Responses & Status Codes

# HTTP Responses

* HTTP responses have the following format:
  * Status line: HTTP version, status code, reason phrase
    * HTTP/1.1 200 OK
  * Headers (optional)
    * Date: Mon, 07 Sep 2020 08:39:33 GMT
    * Content-Type: application/json
  * Body (optional)
* {
* "date": "2020-09-08T11:39:34.2837813+03:00",
* "temperatureC": 11,
* "temperatureF": 51,
* "summary": "Cool"
* }

# Status Codes

* The status line of HTTP a response sent by an API should accurately describe the status of what has happened on the server after each request:
  * Did the operation succeed? (2xx status codes)
  * Was there an error with the request, i.e. the request line was malformed, or the server doesn't support it (4xx status codes)
  * Did a server side exception occur? (5xx status codes)
    * This is never the client's fault

# Status Codes (continued)

Your APIs should use the following status codes for responses to CRUD operations:

| __2xx  SUCCESS__ | __4xx CLIENT ERROR__ | __5xx SERVER ERROR__ |
| :-: | :-: | :-: |
| 200 - OK | 400 - Bad Request | 500 - Internal Server Error |
| 201 - Created | 401 - Unauthorized |  |
| 204 - No Content | 403 - Forbidden |  |
|  | 404 - Not Found |  |
|  | 409 - Conflict |  |

[https://restfulapi.net/http-status-codes/](https://restfulapi.net/http-status-codes/)

# 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.