Examples Using HttpClient in F#
I like F#! It’s got a lot of useful features that helps me write better software.
At times I have a harder time finding documentation and examples. There’s just not as many people using and blogging about it as C#.
This week I was using some F# and had trouble finding examples of using HttpClient in F#. So I decided to fix that problem and blog about it.
Correct HttpClient Usage is Not Simple
Before talking about HttpClient and F#, it’s important to call out that using HttpClient correctly is not simple.
Here are two articles that I’ve read multiple times and still don’t understand all the details.
- You’re using HttpClient Wrong and It Is Destabilizing Your Software
- You’re (probably still) using HttpClient Wrong and It Is Destabilizing Your Software
The underlying problem is that even though HttpClient implements IDisposable it doesn’t get disposed. So creating a new HttpClient for every request can quickly lead to resource starvation if you have high load.
I haven’t used HttpClient enough in F# to recommend best practices, but avoid creating a new HttpClient for every request.
That being said, lets dive into some examples.
I first created a Test API using Giraffe to respond to a GET and POST request.
It fakes the creation of a User, then fakes the retrieving of a User.
Fairly simple stuff.
Then in my F# Console app, I create a User to match what the Test API will return.
The following performs a Get request:
While the following performs a Post request:
Then wire that all up to run each function.
(Check the git repo for a full example)
A couple things to mention:
Async.AwaitTasktransforms the task into F# async type. If you’re using a library like Giraffe to build a web app, using tasks all the way would be a better option.
- I’m creating the HttpClient one time and reusing across both methods. Aim for reusing HttpClients.
- In PostAsync, I’m returning a Result type. Which is a functional way to deal with the ambiguity on whether the http request completed successfully or not.
I hope anyone who uses the HttpClient in F# finds this article a good starting point. As I continue learning F# I’ll continue blogging about the things that I’m learning.