Throttling actions in .Net Core 2.1 using AttributeFilter

I have previously written about Throttling in the pre-core times, and this is sort of the update to that post – with a bit of fixes and tweaks.

Lets get to it;

A few changes:

In my last post I did things a bit differently, for instance; I used to throw a custom exception type and handle that as a response, I have learned that this is an anti-pattern and is strongly discouraged (at least by David Fowler).
Anyway now we return a class, which is basically just my old ApiException type, just without the inherited bits of Exception. – this is both cheaper and cleaner.
Also since we are using .NET Core, we are using IMemoryCache instead of HttpRuntime.Cache – which is also nice.

services.AddMemoryCache();

On to the attribute:

There isn’t a lot to it to be honest.

  1. Check for existence of cache entry
  2. If none, create one and set allowExecute = true
  3. If allowExecute != true, return throttle response and short-circuit the pipeline.

Do note that this throttle uses IP as it’s target, but could easily be username or similar.

Usage:

[IPThrottling("GetItems", 300)]
[HttpGet]
public ActionResult<IEnumerable<string>> Get()
{
    return new string[] { "value1", "value2" };
}

The above throttles for 300 seconds for the GetItems key, so you can group together functionality as well, if you really need to.

Ill talk about the custom response in a different blogpost

Versioning WebApi and documenting version with Swagger

Versioning in WebApi

Note: This post draws alot of points from https://www.troyhunt.com/your-api-versioning-is-wrong-which-is/ – but is more about implementation and documentation through swagger.
So please go read Troy’s post and then come back :).
There are a couple of ways of versioning a restful api
among them are:
1. Url versioning e.g. GET http://example.com/api/v1/cars
2. Request-Header e.g. GET http://example.com/api/cars — Header: api-version: 1
There are pros and cons in both regards, Troy gets around them quite nicely.
Time to code!

Url Versioning

Easy – simply use either the RoutePrefix- or RouteAttribute

Read more about the Routing-Attribute here

Request-Header

Drawing from Troy’s post
We create a new attribute which uses a custom routing constraint

** Usage **

Effectively matching routes based on the “api-version” header.

Swagger

When using swashbuckle (swagger implementation for .Net).
It knows about the default Route- and RoutePrefixAttribute, so Url Versioning is taken care of, out of the box.
But Header versioning is not.
Fortunately, it’s quite easy to implement an OperationFilter that adds the header as a parameter to the endpoints in question.
This implementation uses a list of versions and the endpoints relativepaths to know when to add the parameter and when not to.


How would you implement the OperationFilter?

How to use the autogenerated swagger client

A detailed post on how to use an autogenerated swagger client

This blogpost will focus on the generated C# client.
To get started you basically just need 1 thing.

  1. A Swagger.Json file

Creating the client

If you already have the client you can skip this part
So you have created an API and added Swagger to it or you have been given a swagger.json file or someone else has created a swagger enable API or any combination of the above.
Now you want to create a client for, thankfully http://editor.swagger.io

Can generate a client for you.
Get your swagger.json file (if using swashbuckle the default url for the file is {your api domain}/swagger/docs/v1)
Go the http://editor.swagger.io

swaggerpaste
and paste the swagger.json file into the modal that pops up.
Note:
The editor should notify you of any errors in the schema
For this article I have used the swagger.json from the petstore example (any valid swagger will do).
If no errors arise, you are ready to generate the client.
swaggergenerateclient
Once the zip file is done downloading you should unzip and compile it using the Compile.bat file, located inside the folder.
Once compiled you can find the client and it’s dependencies inside the /bin folder.
Then just add the reference to a new project.
I will be using a basic Console Application.


Using the client

Note: The generated client has 2 dependencies namely; Newtonsoft.Json and RestSharp, these should be referenced through Nuget instead of using the ones that come with the client.
I will provide a basic run-through of how to use the client with different types of authentication, and how to use the generated client.
2 things to note about the client.

  1. All endpoints for the are located in the IO.Swagger.Api namespace
  2. All configuration options for the httpclient is located in the IO.Swagger.Client namespace
    This is where we will provide:

* Authentication
* Default Headers
* UserAgent
* etc.
3. All response models are location in the IO.Swagger.Model namespace
I will start with the configuration as this needs to be out of the way to call the API.

Client Configuration

Authentication:
The examples given are general examples and are not related to the petstore client (apart from the api naming).
I will go through 2 types of Authentication

  1. Basic Authentication
  2. APIKey authentication

Basic Authentication in the generated client is very straightforward

The above example will use the Authorization Header as transport with whatever scheme is defined in the swagger.json file.
Using an APIKey is almost as easy as Basic Authentication:
There are 2 configuration options for apiKey ApiKeyPrefix and ApiKey.
They are both directly related to the header that will be used as transport for the token.

In the above example we are using the Authorization Header as transport and we are using the Bearer Scheme (ApiKeyPrefix)
The sent header will look like the following: Authorization: Bearer {Some token value}

Endpoints

Using the endpoints is almost insanely easy. Every API endpoint is wrapped in a nice easy to use method, with input and output models.
The petstore API uses an api_key header with the value of “special-key” for authentication.
apikeyauth
The code for accessing the store inventory looks as the following

which generates the following output
clientoutput
The code for getting all pets with a particular status (to show the use of output models)

which generates the following output (as of this writing)
Petnames

End

This concludes the post, you should find that using the generated API is pretty straightforward and easy.

Handling Exceptions in WebApi globally

Handling exceptions can be such a hassle. Thankfully the WebAPI pipeline can help alot.
Utilizing the ExceptionFilterAttribute class can create
a consistent and simple way of returning great error responses for your API – like this

Lets get started.

First of all we need:

The Error Model:

The error interface:

We have 4 things here
1. ExceptionType – The type of error
2. A HttpStatusCode – Because returning the statuscode can prove useful to consumers
3. A Code – I use this for the httpstatuscode message
4. A List of Errors
1. Exception Type

Just an enum. I tend to use only Error, but it allows for a more gradient approach if needed.
2. HttpStatusCode
Thankfully the System.Net namespace provides most HttpStatusCodes as enum, so I just utilize this.
3. Code
I use this for the string interpretation of the httpStatusCode, but could be an internal code as well.
4. List of Errors

The above class consists of a Reason phrase and a message to go with this phrase
The “reasons” is also encapsulated as enums, but will be converted into their string representations in the inherited ApiException Class

The derived ApiException Class

Not alot to it. A few constructors, but it should explain itself pretty well.
“All of this is all good and fine, but how do we handle exceptions globally?” you ask.

The GlobalExceptionAttribute


it basically just checks which type of exception was thrown, and acts accordingly, notably typeof(ApiException). Any “unhandled” errors is thrown as “internal server error”. This is also where you would put any logging, as all exceptions will go through this filter. (I have left this out).
The above attribute should be applied in the WebApiConfig.cs file.

As you can see from the following part of the attribute

We check for any errors with typeof(ApiException), but we haven’t implemented the error type yet.
So in any Actions where you would normally return errors, you throw a new ApiException instead.

The above would cause our API to return a response, with a responsecode of 404 and the following body

Throttling actions in WebApi using AttributeFilter

I recently had to come up with a solution to throttle an action in an API i’ve written.
First thing I did was to see what others had used (No reason to invent the wheel right?).
I came across this stackoverflow answer – which is basically what I will use in this blog post (mostly for a reminder to myself I guess).
Full credits go to Jarrod Dixon

The Attribute

The Annotation

Since it’s an attribute, we just annote it to an action
The attribute takes a unique name, amount of seconds and the message to return.
If the action is run more often than allowed, the action will return 409 - conflict