Upgrading from 3.x

This section highlights the most significant breaking changes in Flurl.Http 4.0 and how to adapt your existing code when upgrading.

New Default JSON Serializer

Prior to 4.0, JSON serialization was backed by Newtonsoft.Json. In 4.0, Newtonsoft was dropped in favor of System.Text.Json for the default implementation. There are a few things to look out for when you upgrade:

  • Any serialization attributes defined in Newtonsoft will no longer have any effect, and need be replaced by their STJ equivalents.
  • Any of Newtonsoft's configuration settings you may be using also no longer have any effect in Flurl.
  • There are subtle differences in the default behaviors of the 2 libraries.

Microsoft provides a migration guide that should help you navigate through all of these potential issues. Just be aware that the compiler won't likely catch the sorts of bugs you may encounter, so testing is critical.

"This all sounds painful, I just want to keep using Newtonsoft!"

You're in luck, because there's an alternative: install Flurl.Http.Newtonsoft, a companion package that brings back the 3.x serializer in 4.0 and beyond. Refer to the package readme for details of its usage.

No More Dynamics

dynamic types have somewhat fallen out of favor in the .NET world and are not supported by System.Text.Json. Therefore, all non-generic, dynamic-returning methods like GetJsonAsync() were dropped in 4.0. If you use these methods today, one way forward is to create full-blown classes to replace your dynamics and use generic methods like GetJsonAsync<T>() instead.

But once again, the alternative is installing Flurl.Http.Newtonsoft. Since direct dynamic support still exists in Newtonsoft, those dynamic-returning Flurl methods were ported over to that library.

No More Factories

In Flurl 3.x, you were able to fine-tune behavior by creating and registering custom implementations of IFlurlClientFactory and IHttpClientFactory. Both have been removed in favor of simpler, more fluent ways to achieve the same results, such as configuring the inner HttpMessageHandler and changing the client caching strategy when the clientless pattern is used. Refer to the matrix below for details.

Configuration Changes

Flurl's configuration system got a major overhaul in 4.0, with the goals of making it more fluent, more DI-friendly, and a bit more familiar to those accustomed to using .NET's IHttpClientFactory. This matrix should help you adapt your existing code:

How do I... 3.x 4.0
Configure client or request settings cliOrRequest.Configure cliOrRequest.WithSettings more info
Configure client used to call a specific URL FlurlHttp.ConfigureClient FlurlHttp.ConfigureClientForUrl more info
Configure "global" defaults FlurlHttp.Configure FlurlHttp.Clients.WithDefaults more info
Handle an event cliOrRequest.Settings .BeforeCall[Async] = call => ... cliOrRequest.BeforeCall(call => ...) more info
Configure inner-most HttpMessageHandler Inherit from DefaultHttpClientFactory, override CreateMessageHandler, register factory IFlurlClientBuilder.ConfigureInnerHandler more info
Add a DelegatingHandler Inherit from DefaultHttpClientFactory, override CreateMessageHandler, register factory IFlurlClientBuilder.AddMiddleware more info
Change the client caching strategy Inherit from DefaultFlurlClientFactory, override GetCacheKey, register factory FlurlHttp.UseClientCachingStrategy more info

More Changes

Although this page is not meant to be an exhaustive list of changes in 4.0, the release notes provide such a list. If you encounter a pain point while upgrading that you feel should be better covered here, you're encouraged to edit this page directly using the link below, or open an issue in the docs repo to make a more general suggestion.

Spot an error or omission? Edit this page.