Jan 16 2024

2023 in review

A year of change, and of stability. Let me briefly reminisce and highlight what happened in 2023.


I became an independent maintainer in June 2023. This was a somewhat scary decision, but it did exactly what I hoped it would: my work-life balance feels fantastic. I’m also glad to be able to do similar to what I did at AWS—meeting with and advising teams with serious deployments—but with a wider variety of use cases. (Send me an email if that interests you.)


First, some stats about hyper over the past year. There were 90 unique authors this year, which is 40% growth from 2022! We had two more people sign up to be triagers.

v1 🚀

We released hyper v1 in November. What a ride. It brought changes, moving the less stable side out into hyper-util. But it also signaled a core that won’t be changing any time soon. Stability.

The ecosystem caught up quickly. There were releases for tower-http, headers, and Axum ready to go just a couple weeks after. It enabled some other cool things, like the general availability of the AWS SDK for Rust.

We closed out the year with v1.1, bringing back core pieces needed to make graceful shutdown in servers easier again.


I reviewed at least 10 security reports, perhaps a couple more I didn’t keep track of. This includes the wider HTTP/2 rapid reset attack that hyper wasn’t affected by. The amount of time I spend on security reports keeps on increasing. That makes sense, we announced stability of v1, which surely made more people take a look. It also is a sign of more production deployments, with companies wanting to audit their dependencies.


Another priority this year was to make progress on hyper’s HTTP/3 support, currently under development in the h3 crate. We released some initial 0.0.1 releases (and a few more subsequent ones), specifically to make it easier for people to use. reqwest gained unstable HTTP/3 support, using h3, and some brave users have enabled it, found it working well, and are now asking if we can make it stable. A couple of other fine folks worked to make the h3-webtransport crate, building on top of h3.

Future Focus

Doing a bit forward looking, what’s the plan for 2024? Well, of course it could change at any moment, but these seem to be the things people most ask me for, and most need.

HTTP/3 in hyper

I hope to make significant progress towards getting HTTP/3 support directly in hyper. I’ll work on a proper proposal, but here’s some unordered steps in that direction. Stabilizing the feature in reqwest. Set up an auto-updating h3 server for interop testing. Dig away at the compliance report, both by labeling more of the parts already working, and adding any missing parts. Propose how to expose it in hyper, which will be tricky so as to not tie hyper to any specific TLS library. And then get it actually added, likely as a hyper_unstable_h3 feature to start.

Level up Client middleware

There’s a lot of great middleware now. But it can still feel like it requires an expert to use it properly. I’ve been hinting at for a while that I’d like to do for clients what Axum has done for servers. I hope to do that with reqwest.

reqwest does a lot of useful things, but if someone wants to customizing it beyond the options that reqwest exposes, they have to reimplement a lot (or live with a fork). I want to make most of reqwest’s features tower middleware. reqwest will still have a standard “recommended” client. But it should be easier to build up your own custom stack.

And while we’re at it, I hope to make some of the most important and yet most difficult middleware much easier to sprinkle in: retries, limits, and load balancing.

On-going maintenance

I also must carve out explicit time for maintenance work. There’s bugs that need fixing. Reviewing and triage takes a lot of my energy. I want to improve the docs and guides. The amount of security reports received is growing, and those take time to investigate and respond or patch and disclose, depending on their validity and severity. This also includes time with my sponsors, which helps identify maintenance work priorities.

Want to join us?

Nov 15 2023

hyper v1

I’m excited to announce v1.0 of hyper, a protective and efficient HTTP library written in the Rust programming language. hyper provides asynchronous HTTP/1 and HTTP/2 server and client APIs, allowing you to bring your own IO and runtime.

It’s been exciting and humbling to watch users build awesome things. Cloudflare uses hyper within Oxy, its next generation proxy framework to handle traffic at considerable scale. After Discord’s 5x improvement to @mention response times a few years ago, they have moved most of their critical systems to depend on Rust and hyper. curl has a currently experimental HTTP backend built on hyper with the goal of making the Internet safer.

Marc Brooker, a Distinguished Engineer at AWS, commented:

When building our new container-loading data plane for AWS Lambda, we expected to need a custom binary protocol. In production, we’ve found the overhead of hyper to be SO low that we are excited for it to continue powering our services.

Johan Andersson, CTO at Embark, said:

We have been using and relying on hyper for the last 5 years for our gRPC and REST services, tools, libraries, and embedded in our next game built in Rust. It has been rock solid across all of our usages, and it really is a foundational library for the Rust ecosystem. Congrats on 1.0!

The best way to get started is to check out the guide.

Stability here we come

Over the past 9 years, hyper has grown from a web developer’s side project into a solid library powering huge network applications. It’s time to grow up. After bringing async/await support in v0.14, we focused on providing a set of basic APIs that would keep hyper safe, fast, and flexible. This meant removing some of the more opinionated “higher level” pieces. Those belong elsewhere, like hyper-util, reqwest, Axum.

This release signals some stability. Major versions, like 1.0, are stable for at least 3 years.1 We also keep a MSRV that is at least 6 months old.2 We’ll add new features, and we still have a couple places to experiment: in the hyper-util crate, and hyper_unstable compiler flags.

Starting in v0.14.25, we added a backports feature which brings the new core APIs to you immediately. Combine that with the deprecated feature, and you’ll be guided to making your existing code ready for the upgrade to 1.0. Be sure to check out the upgrade guide!


The most immediate next steps are to update the other core parts of the ecosystem that depend on hyper: reqwest, Axum, Tonic. But after that, there’s plenty more to do. You’re welcome to come join us!


I would like this to be my next focus. We’ve been building up the h3 crate, and reqwest has unstable support now. I’d like to stabilize the feature in reqwest, and explore how we can make it available in hyper directly. Then we can have easy HTTP/3 servers, too!

The trickiest question is making it available without being tied to a TLS/QUIC library. Then, users could choose to use quinn, or s2n-quic, or msquic, or any other.

Stabilize in curl

The biggest parts of making hyper work in curl are done. Someone with experience in Rust and C could make a huge dent in Internet safety helping to get it over the finish line.


There’s some excellent middleware available already in tower and tower-http. But several of the important ones are just a little (or a lottle) too difficult to add to a stack. I’d also love for there to be some recommended stacks for servers and clients, that bundle together the right middleware that most people would need. To that end, I’ve mentioned before breaking open reqwest such that all of its features are middleware you can customize.

Tracing and Metrics

It’s possible to currently get a decent set of logs using tower_http::trace. It’d be better if you could get more fine-grained traces and metrics. Probably with some stabilized integration with tracing directly in hyper. Maybe some sort of hyper-metrics, similar to tokio-metrics.


Part of the reason we made hyper have its own IO traits was to be able to adapt them for completion-based IO. I believe having decent support and benchmarks could be had pretty soon, by a motivated individual.


A huge thank you to all our amazing contributors. You’ve made this project the success it is, and helped move hyper along the journey to 1.0. I’d like to follow up with a separate post specifically thanking you all.

Thanks to the companies who have sponsored the creation of hyper: AWS, Buoyant, Mozilla, Rust Foundation, Fly.io, Embark and others.

Your company could also become a sponsor or get support!

  1. Besides some correctness mistake that must be fixed ASAP. 

  2. We realize that some users just cannot upgrade that fast, and we care about them. 

Oct 10 2023

hyper HTTP/2 Rapid Reset Attack: Unaffected

Today, the world has been made aware of a potential vulnerability affecting most HTTP/2 implementations, sending a rapid amount of streams and resets.

If you use hyper, even just it’s h2 dependency, you are safe. hyper is not affected. Especially if you have h2 v0.3.18 or newer. We manually verified that an example hyper server responds correctly. Big thanks to @Noah-Kennedy for all the help.

If you want to read more, checkout CVE-2023-44487, or these other breakdowns.

That’s it!

You’re still here. You want to know the “why”?

Well, for two main reasons.

We added in specific detection of this problem back in April. A related flaw was reported against hyper, with the added requirement of a consistently flooded network. We fixed that. It had a CVE and RUSTSEC advisory for it, so you should have upgraded, right?

But even without that fix, the damage that could be done was local. The bigger concern of this newly announced vulnerability seems to be when the receipt of the HEADERS frame triggers more work in the handlers that needs to then be canceled. The way hyper handles frames, it will cancel out the stream before ever making it available for handlers, so the cost is local. Without the fix, and only if the user can flood the network, then hyper could consume a lot of memory keeping track of all the suddenly reset streams. If they can’t flood the network, then no problem at all.

So if you’ve upgraded since April, you’re safe. By the way…

Handling security by dealing with reports, and working with coordinated disclosures like today are a significant part of maintaining hyper. If you appreciate that hyper is kept secure, consider sponsoring. Being able to have more support during security disclosures is something that you can setup with me privately.

Sep 28 2023

Was async fn a mistake?

This stabilization PR for async fn in traits made me think: was async fn in Rust a mistake?

I mean, I dunno. Maybe it wasn’t. But play along for a moment.

By the way, I don’t mean that async/await in Rust itself is a mistake. That’s a Big Deal. It allows companies to deploy some serious stuff to production. And async and await syntax is a huge save. I don’t want to lose that. Writing manual futures and poll functions is megasad.

I’m specifically talking about the async fn sugar. What if we didn’t have it, and instead just returned impl Futures, and used async blocks inside the functions?1

The current async fn is really nice, if you fit the expected usage. If none of the differences with impl Future ever cause you problems, then great! But I do run into them. Other people seem to also.

What’s so bad?

Some of these differences cause problems that don’t have decent solutions. (Do you know the differences?)2 If you have to deal with one of them, suddenly you need to use different syntax.

And now, people need to understand both. And keep the subtle differences in their head when they read. Does that make things better? Or worse?

It’s the only place that has a magic return type. It makes lifetimes weird. With suggestions to reign them in. It leads to all sort of proposals about how to customize the return type. #[require_send], async(Send), Service::call(): Send, and I’m sure there’s others.3 I also am thinking about generators and streams, since they could also end up with magic return values.

So was it mistake? I think it may have been. Don’t worry, I don’t want to take it away from you, if you disagree!4

What if the alternative was nicer?

But I did wonder about this. What if we had the following features ready:

  • Repurpose bare trait syntax to mean impl Trait. It’s been enough editions, right?
  • Ability to forgo naming an associated type name.
  • Stealing the feature from Scala where functions can equal a single expression.

Then asynchronous functions could look like this:

fn call(&self, req: Request) -> Future<Response> = async {
    // ...

That’d be a nice improvement.

  1. Yea, I know, it’s a little more writing. But I am in the optimize-for-reading camp. We read much more than we write. So if I have to write a few more characters at a function definition, but it makes the reading experience more understandable, that’s a massive win. 

  2. I’ve been involved in async Rust since the beginning. I know how it used to be, I was part of the group making it better, and I pay close attention to all the new proposals. I still mean what I said: none of the solutions look nice. 

  3. Return Type Notation (RTN) syntax is probably the least gross. But it raises a bunch of questions. Does it work for all functions? If not, why not? If so, do I check I::Iter or I::into_iter(). And also to consider: Rust’s strangeness budget

  4. I could see an argument that it’s sort of like for, while, and loop. A more convenient syntax when it works, and you can use the others when you need more control. That argument breaks down when async fn is part of a trait definition. But anyways, I really just want the less-sugared way to be little nicer. 

Jul 27 2023

I'm an independent open source maintainer

tl;dr - I’m independent, sponsor me!

I’m doing something new. I’m an independent open source maintainer! In the beginning of June, I left my position at AWS.1

I’m still focused on Rust, async, and HTTP stuff. Projects like hyper, reqwest, h3, tower, and any other new ideas that come along. I just won’t be doing so as an employee.

So, then how do I get paid? Let me just clear up a couple ways I’m not. I’m not making separate licenses. I’m not charging for features.2 I’m not selling prioritization on roadmaps. Rather, I plan to make maintenance work my primary focus.

Maintenance can feel like riding a squared unicycle while juggling water balloons. Some of those balloons are:3

  • Designing proposals, interviewing users, re-writing those proposals.
  • Coding, coding, coding.
  • Triaging a never-ending supply of issues.
  • Spelunking in ancient code paths to understand and fix weird bugs.
  • Following a proper security policy with responsible disclosure, collaborating privately, and preparing detailed reports.
  • Reviewing pull requests for quality and sticking to the vision, and hopefully teaching potential collaborators.
  • Writing articles and giving talks, as a form of marketing and teaching.
  • Pretending to be a project manager.

It’s a lot of work, so who would pay for all that?

Does your company depend on my work? Become a sponsor! Consider it a form of business risk mitigation. You can use GitHub Sponsors or Patreon. I can also work with an invoice system, for any requiring that.

I am also interested in some deeper relationships with companies that want more. What exactly those relationships will look like will evolve. It would likely be things that look like office hours, support or private advice. If you want to explore that with me, reach out at sean@seanmonstar.com.

  1. I learned a lot from my 3 years at AWS. Many lessons, some anti-lessons. Overall, I’m very grateful for my time there. But I had been planning this change for a while. And it was quite refreshing taking off a few weeks before jumping back into it all. 

  2. A win about being independent is that no single company is deciding what features should be added. 

  3. This would be a good subject for another article. There’s a lot more to it, and it’d probably be surprising to people how many hats are needed to maintain popular open source libraries, besides “just being a programmer”. At least, if you want to do it well.