Announcing axum 0.8.0

Happy new year! 🎉

Today, we're happy to announce axum version 0.8. axum is an ergonomic and modular web framework built with tokio, tower, and hyper.

This also includes new major versions of axum-core, axum-extra, and axum-macros.

Here is a small selection of the most notable changes in this release:

Path parameter syntax changes

The path parameter syntax has changed from /:single and /*many to /{single} and /{*many}.

There are many reasons for this change, but the most important one is that the old syntax was not allowing route definitions with leading : or * characters.

This new syntax was introduced with our upgrade to matchit 0.8. It should feel somewhat familiar from the format!() macro, and it's also the syntax that is being used in OpenAPI descriptions. Escaping is done with double braces, so if you want to match a literal { or } character, you can do so by writing {{ or }}.

We understand that this is a breaking change for basically all axum users, but we believe that it's better to make this change now than to have to do it later when even more users depend on the old syntax. The migration path should also be relatively straightforward, so we hope that this change won't cause too much trouble for you.

You can find more information and migration examples in the corresponding pull request. Thank you to David Mládek for the implementation in axum and to Ibraheem Ahmed for your continued work on matchit.

Option<T> as an extractor

The way Option<T> is used as an extractor has changed. Previously, any rejections from the T extractor were simply ignored and turned into None.

Now, Option<T> as an extractor requires T to implement the new trait OptionalFromRequestParts (or OptionalFromRequest).

This makes it possible to handle rejections from the T extractor and turn them into error responses, while still allowing extractors to be optional.

Imagine you have an AuthenticatedUser extractor that requires a valid token to be present in the request, but in some cases authentication is optional. You can now use Option<AuthenticatedUser> as an extractor without losing the ability to return an error response if the token is invalid or the database connection failed.

Thank you to Jonas Platte for the pull request that introduced this new capability.

#[async_trait] removal

In late 2023, the Rust team made it possible to use impl Future<Output = _> in traits. This feature is called return-position impl Trait in traits. and means that we no longer need the #[async_trait] macro to define async methods in traits.

This change primarily affects our FromRequestParts and FromRequest traits, since they use async methods. If you have custom extractors that implement these traits, you will need to remove the #[async_trait] annotation from them.

This change was implemented by Zheng Li. Thank you for your contribution!

See the changelog for more

There are many more changes in this release, including new features, bug fixes, and less visible breaking changes. We encourage you to read the changelog to see all the changes!

Also, please open a GitHub discussion if you have trouble updating. You're also welcome to ask questions in Discord.

Finally, we want to thank all the contributors who helped make this release possible. Your work is greatly appreciated!