COMPUTING SUBJECT: Restful ASP.Net Core-services
TYPE: Assignment
IDENTIFICATION: RestCalculatorService
COPYRIGHT: Michael Claudius & Peter Levinsky
LEVEL: Medium
TIME CONSUMPTION: 2-5 hours
EXTENT: 60 lines
OBJECTIVE: Restful services based on ASP.Net
Core
PRECONDITIONS: Rest service theory. Http-concepts
Computer
Networks Ch. 2.2
Telerik
Fiddler installed
COMMANDS:
IDENTIFICATION: RestCalculator /MICL&PELE
Purpose
The purpose of this
assignment is to be able to provide and consume restful ASP.Net Core web
services.
Secondary purpose is to utilize the web debugging tool Fiddler. Before start
reading more you mus watch the video and install Fiddler:
Video: https://www.telerik.com/videos/fiddler
Download: https://www.telerik.com/fiddler
Mission
You are to make and use restful web services
based on the ASP.Net Core services by setting up a server (provider), test the
services by use of Fiddler/Postman and create a client (consumer) using the services
provided. On the way you will publish the service to the cloud (Azure). The
service supports the classic GET, POST, PUT and DELETE requests. This we shall
do in 12 steps:
1.
Create
a project with auto generated service: api/values
2.
Test
the services using Browser
3.
Test
the services using Fiddler/Postman
4.
Investigate
various possibilities in the Solution Explorer and Execution mode.
5.
Create
a model class Data for holding numbers
6.
Create
a controller CalculatorController to provide a REST services
7.
Create
and provide a controller oriented service in CalculatorController
8.
Test
the service using Fiddler/Postman
9.
More
services and testing by Fiddler/Postman
10.
Create
a client/consumer utilizing the services
11.
Publish
the service to Azure
12.
Refactoring
the consumer code
This assignment holds all 12 steps,
where the first 4 is more like a tutorial done and guided by your teacher and
the last ones you are doing more independently.
Later in another assignment, RestCustomerService, you will create a Rest
service for management and administration of customer-objects, and in last
assignment, RestCustomerService No. 2, learn elementary unit testing and how to
support Cross Origin Resource Sharing (CORS).
Domain description
First (1-4), we shall just utilize the simple
auto generated web service defined by ValuesContolller.
Second (5-12), we shall program web services
for the four the basic arithmetic calculation of two integers (a,b):
Addition(a+b), Subtraction(a-b), Multiplication(a*b)
and division(a/b).
When
surfing on the net it is easy to find many descriptions more or less useful,
and in more or less updated versions. Here are some:
Useful links for C#:
Serializable Class
https://msdn.microsoft.com/en-us/library/4abbf6k0(v=vs.110).aspx
CRUD-Operations
and routing
https://docs.microsoft.com/en-us/aspnet/web-api/overview/web-api-routing-and-actions/attribute-routing-in-web-api-2
Useful links for Fiddler:
Video
https://www.telerik.com/videos/fiddler
Download
https://www.telerik.com/fiddler
Assignment
1: Restful ASP.Net Framework-service provider
You are to make a Rest
Service provider RestCalculatorService.
Start Visual
Studio:File -> New -> Project.
Choose: Web -> ASP.NET Core Web Application (not .Net
Framework).
Browse to a convenient
location and give the name RestCalculatorService.
Click OK.
Now a project template
with options is given.
Choose the API.
DON’T tick Docker support.
Tick HTTPS if you intend to use GoogleChrome or MicrosoftEdge as browser. And
Fiddler as a tester-client. This has been tested by me (Michael Claudius) and
it all works fine.
Don’t tick HTTPS, if you intend to use Firefox as browser. And
maybe, maybe not Postman, as it can have problems using https. But then of
course https will NOT be supported
later on.
Now you have to wait a
while…
Then we are ready to
investigate the created project.
Assignment 2: Execute
the web application
Execute the
web application (click the green arrow as usually) and it will open a local
Browser.
As you can
see the application is running on port 44343 on my computer (it will be
different on yours).
Try to give
the url:
http://localhost:44343/api/values/5
and
http://localhost:44343/api/values/17
Note probably
another port number and note also what you indicate as route is part of your
URL to the Rest Service.
What do you
get ?
Assignment 3:
Fiddler/Postman
Now we will
try to invoke the methods from Fiddler/Postman using the same url’s as before.
Start
Fiddler
Be aware
that you must:
a.
Click
on Composer
b.
Choose
GET
c.
Copy
and paste the url from Browser (http://localhost:44343/api/values) into the text field
It will
look something like this:
Then
a.
Click on
Execute
b.
Double
Click the “200 HTTPS” response line in the left column
And hopefully you will
see something like this:
Finally click on Headers
and Raw you can see the HTTP response.
Notice the
“Content-Type: application/json; charset=utf-8”
Notice the JSON body ["value1","value2"]
What does the [] stand for ?
Assignment 4:
Exploring the set up
Some questions arise:
Why does the project start with api/values?
Where are the
methods defined?
Why is it port 44343?
How can it be executed in console mode on a different port?
To find the answers
take a look in Solution Explorer:
Controller ->
ValuesController
Propeties ->
LaunchSettings.json
Try to change the Get
method to
[HttpGet("{id}")]
public ActionResult<int> Get(int id)
{return id;}
Execute again. Any
difference? What happens?
Finally, change
IISExpress to RestCalculatorService and run the application again.
What could be the
purpose of doing this?
This ends the investigation of the auto generated
service.
In the next assignments you shall create your
own service.
Assignment 5: Model
class Data
We need a class with
two integers so arithmetic operations can be performed on objects of this
class. Therefore to the project add (right click project, choose Add ->
Folder) a folder named “Model” and in this folder add a public class, “Data”,
with the data fields:
int A; int B
with get/set method
for all the fields; i.e. they are properties.
Create the
constructors:
Data(int a, int
b)
Intializing all the data fields
Data() {}
//empty constructor needed for JSON transfer. Serializable objects.
Assignment 6: REST API operation by creating a controller
You are to create a controller where the operation
contracts must be defined as REST API routes and methods similar to
ValuesController
In the solution in the
controller folder, add (i.e. Right click) a new controller named “CalculatorController”.
Choose ‘Web API Controller with
read/write actions’.
Click Add
and you can see the new controller.
Assignment
7: Defining Service Add
In CalculatorController define a new
operation contract to support a Rest API POST request:
// POST: api/Calculator
[HttpPost("Add", Name = "Add")]
public int Post([FromBody] Data data)
{
return data.A + data.B;
}
And
implement the method to return the sum of the integers in the data object.
What is the
full route to the Add operation?
Why did we
choose to change HttpPost?
Execute the
Application by viewing it in a local Browser. This will start the Azure
emulator.
From the
browser call the calculator:
http://localhost:44343/api/calculator
http://localhost:44343/api/calculator/add
Note probably another port number and note also what you indicate as
route is part of your URL to the Rest Service.
All fine?!.
Nope…Really
boring right!!?
Assignment
8: Running from Fiddler/Postman
Try to
invoke the method from Fiddler/Postman
Be aware
that you must:
d.
Click
on Composer
e.
Choose
POST
f.
Define
the Content-Type: application/json
g.
Request
body must hold the data as a json-string like: {“A”:27,”B”:4}
h.
Click
on Execute
It will
look something like this:
Click on Execute and hopefully you get the sum.
Note: Fiddler might be limited to only use the
IISExpress version (one student out of 50 will encounter this problem L)
Assignment
9: More services
You must
now extend the service (i.e. your controller) with more methods.
In
CalculatorController define more operations handling
a. Subtraction
a-b
b. Multiplication
a*b
c. Division a/b
Remember for each method you must
carefully think about
- Which HTTP method/verb to use?
- What should the URI (Route)
look like? Any parameters to the URI, like {id}?
- Return type: true/false, customer
object, id etc..
And write down your arguments.
For each method, show how to use it
from Fiddler/Postman.
Assignment
10: Program for consuming services: RestCalculatorConsumer
Create a
simple Console Application project. Add Data class to the project, similar to
the one you used in the provider.
In order to
serialize/deserialize objects, you must
from NuGet install the package Newtonsoft.json.
Now to
consume the “Add” service, you in Program class (i.e. Not inside main) make a very special method:
public static async Task<string> AsyncAdd(Data
data)
{
using (HttpClient client = new HttpClient())
{
Console.WriteLine("Data
" + data);
var jsonString = JsonConvert.SerializeObject(data);
Console.WriteLine("json
string: " + jsonString);
StringContent content = new
StringContent(jsonString, Encoding.UTF8, "application/json");
Console.WriteLine("content: :
" +
content.ToString());
Console.WriteLine("CalculatorUri:
" + CalculatorUri);
HttpResponseMessage response = await
client.PostAsync(CalculatorUri + "Add", content);
string str = await response.Content.ReadAsStringAsync();
//Int32 sumStr =
JsonConvert.DeserializeObject<Int32>(str);
return str;
}
}
Where the
CalculatorUri is the URI pointing to your service and method (api/calculator).
a. In main show how to use the method and
print out the sum of two integers.
Execute the program.
Tip: You need to get
the Result value of the asynchronous Task and then change the type from string
to integer.
b. Carefully
explain the code line-by-line what goes on.
c. More calculations
Extend the program with similar methods handle the other arithmetic
calculations.
Show also how to use these methods in main.
Assignment 11: Publish
in Azure
a.
Publish your service in Microsoft Azure.
b.
Use a browser to show the API and the methods.
Assignment 12:
Refactor the consumer code
Refactoring
is about making the code either smarter or downsizing the number of code lines!
Take a look at your consumer code.
There is a
lot of redundant code.
Can you do
something about it?!