HTTTP/Middleware/MVC

Question 1

Kestrel

Answer 1

Kestrel is a cross-platform web server for ASP.NET Core, a web framework for building modern, cloud-based, and internet-connected applications. It is the default web server included with ASP.NET Core projects and is designed to be lightweight, high-performance, and scalable.

Question 2

Reverse proxy servers- examples

Answer 2

IIS
Nginx
Apache

Reverse proxy to serwer, który przyjmuje żądania HTTP od klientów (np. przeglądarek) i przekazuje je do jednego lub więcej serwerów aplikacji w celu przetworzenia. Odpowiedzi z serwera aplikacji są następnie wysyłane z powrotem do klienta przez serwer proxy. W przeciwieństwie do forward proxy, który działa w imieniu klienta, reverse proxy działa w imieniu serwera.

Question 3

Benefits of Reverse Proxy Servers

Answer 3

Load Balancing
Caching
URL Rewriting
Decompressing the requests
Authentication
Decryption of SSL Certificates

Question 4

IIS express benefits

Answer 4

HTTP access logs
Port sharing
Windows authentication
Management console
Process activation
Configuration API
Request filters
HTTP redirect rules

Question 5

HTTP

Answer 5

is an application-protocol that defines set of rules to send request from browser to server and send response from server to browser.

Question 6

HTTP Response Status Codes

Answer 6

1xx | Informational
101 Switching Protocols

2xx | Success
200 OK

3xx | Redirection
302 Found
304 Not Modified

4xx | Client error
400 Bad Request
401 Unauthorized
404 Not Found

5xx | Server error
500 Internal Server Error

Question 7

Response Start Line

Answer 7

Includes HTTP version, status code and status description.

HTTP Version: 1/1 | 2 | 3

Status Code: 101 | 200 | 302 | 400 | 401 | 404 | 500

Status Description: Switching Protocols | OK | Found | Bad Request | Unauthorized | Not Found | Internal Server Error

Question 8

HTTP Response Headers

Answer 8

Date
Date and time of the response. Ex: Tue, 15 Nov 1994 08:12:31 GMT

Server
Name of the server.
Ex: Server=Kestrel

Content-Type
MIME type of response body.
Ex: text/plain, text/html, application/json, application/xml etc.

Content-Length
Length (bytes) of response body.
Ex: 100

Cache-Control
Indicates number of seconds that the response can be cached at the browser.
Ex: max-age=60

Set-Cookie
Contains cookies to send to browser.
Ex: x=10

Question 9

HTTP Request Methods

Answer 9

GET
Requests to retrieve information (page, entity object or a static file).

Post
Sends an entity object to server; generally, it will be inserted into the database.

Put
Sends an entity object to server; generally updates all properties (full-update) it in the database.

Patch
Sends an entity object to server; generally updates few properties (partial-update) it in the database.

Delete
Requests to delete an entity in the database.

Question 10

GET request

Answer 10

Used to retrieve data from server.

Parameters will be in the request url (as query string only).

Can send limited number of characters only to server. Max: 2048 characters

Used mostly as a default method of request for retrieving page, static files etc.

Can be cached by browsers / search engines.

Question 11

POST request

Answer 11

Used to insert data into server

Parameters will be in the request body (as query string, json, xml or form-data).

Can send unlimited data to server.

Mostly used for form submission / XHR calls

Can’t be cached by browsers / search engines.

Question 12

Middleware

Answer 12

Middleware is a component that is assembled into the application pipeline to handle requests and responses.

Middlewares are chained one-after-other and execute in the same sequence how they’re added.

Middleware can be a request delegate (anonymous method or lambda expression) [or] a class.

Http Context + Next

Question 13

Middleware - Run
app.Run( )

Answer 13

The extension method called “Run” is used to execute a terminating / short-circuiting middleware that doesn’t forward the request to the next middleware.

Question 14

app.Use( )

Answer 14

The extension method called “Use” is used to execute a non-terminating / short-circuiting middleware that may / may not forward the request to the next middleware.

Question 15

Middleware Class

Answer 15

class MiddlewareClassName : IMiddleware
{
public async Task InvokeAsync(HttpContext context, RequestDelegate next)
{
//before logic
await next(context);
//after logic
}
}
app.UseMiddleware<MiddlewareClassName>();</MiddlewareClassName>

Middleware extension method is used to invoke the middleware with a single method call.

Question 16

Middleware chain

Answer 16

app.UseExceptionHandler(“/Error”);
app.UseHsts();
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseCors();
app.UseAuthentication();
app.UseAuthorization();
app.UseSession();
app.MapControllers();
//add your custom middlewares
app.Run();

Question 17

Middleware - UseWhen

Answer 17

app.UseWhen(
context => { return boolean; },
app =>
{
//add your middlewares
}
);

The extension method called “UseWhen” is used to execute a branch of middleware only when the specified condition is true.

Question 18

Routing

Answer 18

Routing is a process of matching incoming HTTP requests by checking the HTTP method and url; and then invoking corresponding endpoints.

Question 19

Default Route Parameters

Answer 19

“{parameter=default_value}”

A route parameter with default value matches with any value.

It also matches with empty value. In this case, the default value will be considered into the parameter.

Question 20

Optional Route Parameters

Answer 20

“{parameter?}”

”?” indicates an optional parameter.

That means, it matches with a value or empty value also.

Question 21

Custom Route Constraint Classes

Answer 21

public class ClassName : IRouteConstraint
{
public bool Match(HttpContext? HttpContext, IRouter? route, string routeKey, RouteValueDictionary values, RouteDirection routeDirection)
{
//return true or false
}
}

Question 22

Endpoint Selection Order

Answer 22

1: URL template with more segments.

Eg: “a/b/c/d” is higher than “a/b/c”.

2: URL template with literal text has more precedence than a parameter segment.
Eg: “a/b” is higher than “a/{parameter}”.

3: URL template that has a parameter segment with constraints has more precedence than a parameter segment without constraints.
Eg: “a/b:int” is higher than “a/b”.

4: Catch-all parameters ().
Eg: “a/{b}” is higher than “a/”.

Question 23

Controller

Answer 23

Controller is a class that is used to group-up a set of actions (or action methods ).

Action methods do perform certain operation when a request is received & returns the result (response).

Controllers should be either or both:

The class name should be suffixed with “Controller”. Eg: HomeController

The [Controller] attribute is applied to the same class or to its base class.

Controller

[Controller]
class ClassNameController
{
//action methods here
}

Optional:
Is a public class.
Inherited from Microsoft.AspNetCore.Mvc.Controller.

Question 24

Responsibilities of Controllers

Answer 24

Reading requests

Extracting data values from request such as query string parameters, request body, request cookies, request headers etc.

Invoking models
Calling business logic methods.
Generally business operations are available as ‘services’.

Validation
Validate incoming request details (query string parameters, request body, request cookies, request headers etc.)

Preparing Response
Choosing what kind of response has to be sent to the client & also preparing the response (action result ).

Question 25

IActionResult

Answer 25

It is the parent interface for all action result classes such as ContentResult, JsonResult, RedirectResult, StatusCodeResult, ViewResult etc.

By mentioning the return type as IActionResult, you can return either of the subtypes of IActionResult

Question 26

Model Binding

Answer 26

Model Binding is a feature of asp.net core that reads values from http requests and pass them as arguments to the action method.

Question 27

Models

Answer 27

Model is a class that represents structure of data (as properties) that you would like to receive from the request and/or send to the response.

Also known as POCO (Plain Old CLR Objects).

Question 28

Model Validation

Answer 28

class ClassName
{
[Attribute] //applies validation rule on this property
public type PropertyName { get; set; }
}

IsValid
Specifies whether there is at least one validation error or not (true or false).

Values
Contains each model property value with corresponding “Errors” property that contains list of validation errors of that model property.

ErrorCount
Returns number of errors.

Question 29

Model Validation examples

Answer 29

[Required(ErrorMessage = “value”)]
Specifies that the property value is required (can’t be blank or empty).

[StringLength(int maximumLength, MinimumLength = value, ErrorMessage = “value”)]
Specifies minimum and maximum length (number of characters) allowed in the string.

[Range(int minimum, int maximum, ErrorMessage = “value”)]
Specifies minimum and maximum numerical value allowed.

[RegularExpression(string pattern, ErrorMessage = “value”)]
Specifies the valid pattern (regular expression).

[EmailAddress(ErrorMessage = “value”)]
Specifies that the value should be a valid email address.

[Phone(ErrorMessage = “value”)]
Specifies that the value should be a valid phone number).
Eg: (999)-999-9999 or 9876543210

[Compare(string otherProperty, ErrorMessage = “value”)]
Specifies that the values of current property and other property should be same.

[Url(ErrorMessage = “value”)]
Specifies that the value should be a valid url (website address).
Eg: http://www.example.com

[ValidateNever]
Specifies that the property should not be validated (excludes the property from model validation).

Question 30

Custom Validations

Answer 30

class ClassName : ValidationAttribute
{
public override ValidationResult? IsValid(object? value, ValidationContext validationContext)
{
//return ValidationResult.Success;
//[or] return new ValidationResult(“error message”);
}
}

Question 31

IValidatableObject

Answer 31

Base class for model classes with validation.

Provides a method called Validate() to define class level validation logic.

The Validate() method executes after validating all property-level validations are executed; but doesn’t execute if at least one property-level validations result error.