build: remove axum dependency and use hyper directly by m4tx · Pull Request #711 · cot-rs/cot

m4tx · 2026-10-18T15:47:11Z

Related issue or discussion

Fixes #182.

Description

Cot only used axum for axum::serve and its body type, so this replaces it with a small accept loop built on hyper and hyper-util.

cot_core no longer depends on axum (nor hyper) at all; incoming request bodies are stored as a type-erased http_body::Body. This removes axum from the critical path of a cold build, as cot_core doesn't need to wait for axum/hyper to be compiled anymore.

Note that axum-core is still pulled in by tower-session. This is blocked on a tower-sessions change: maxcountryman/tower-sessions#270.

On my machine (16-thread AMD Ryzen 7 PRO 7840U, 64GB of RAM, power saving mode) and --no-default-features, the build goes from 25.4sec to 22.1sec (so around 13% saving). The saving should be pretty consistent even with a lot of CPU cores, because axum was on the critical build path.

Type of change

Checklist

I've read the contributing guide
Tests pass locally (just test-all)
Code passes clippy (just clippy)
Code is properly formatted (cargo fmt)
New tests added (regression test for bugs, coverage for new features)
Documentation (both code and site) updated (if applicable)

github-actions · 2026-10-18T15:51:43Z

Bencher Report

Project	cot
Branch	build/remove-axum
Testbed	github-ubuntu-latest

Click to view all benchmark results

Benchmark	Latency	Benchmark Result microseconds (µs) (Result Δ%)	Upper Boundary microseconds (µs) (Limit %)
empty_router/empty_router	📈 view plot 🚷 view threshold	7,267.80 µs (-40.89%) Baseline: 12,296.05 µs	18,508.91 µs (39.27%)
json_api/json_api	📈 view plot 🚷 view threshold	730.37 µs (-27.45%) Baseline: 1,006.77 µs	1,345.38 µs (54.29%)
nested_routers/nested_routers	📈 view plot 🚷 view threshold	715.76 µs (-24.74%) Baseline: 951.05 µs	1,254.98 µs (57.03%)
single_root_route/single_root_route	📈 view plot 🚷 view threshold	672.27 µs (-26.14%) Baseline: 910.18 µs	1,209.60 µs (55.58%)
single_root_route_burst/single_root_route_burst	📈 view plot 🚷 view threshold	13,238.00 µs (-21.26%) Baseline: 16,811.28 µs	22,263.31 µs (59.46%)

🐰 View full continuous benchmarking report in Bencher

codecov · 2026-10-18T16:02:27Z

Codecov Report

❌ Patch coverage is 90.45455% with 21 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cot/src/project.rs	88.74%	14 Missing and 3 partials ⚠️
cot-core/src/body.rs	92.98%	4 Missing ⚠️

Flag	Coverage Δ
rust	`90.98% <90.45%> (+<0.01%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
cot/src/error_page.rs	`91.31% <100.00%> (-0.64%)`	⬇️
cot-core/src/body.rs	`89.00% <92.98%> (+3.79%)`	⬆️
cot/src/project.rs	`87.29% <88.74%> (+0.42%)`	⬆️

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m4tx · 2026-10-18T16:03:38Z

As a test to ensure that the change works correctly, I'm now running https://mackow.ski with this patch (m4tx/m4txblog#70).

Copilot

🟡 Changes recommended

The new server loop leaves the listener open during shutdown and does not preserve HTTP upgrade support.

2 open issues

What changed in this PR

Replaces Axum with Hyper for HTTP serving and decouples cot-core request bodies from either server library, addressing #182 and reducing build dependencies.

Changes:

Adds a Hyper accept loop with graceful shutdown.
Uses type-erased incoming bodies and native Cot responses.
Updates dependencies and framework documentation.

File	Description
docs/framework-comparison.md	Describes Hyper/Tokio foundations.
cot/src/project.rs	Replaces Axum serving and response adapters.
cot/src/lib.rs	Updates framework foundation documentation.
cot/src/error_page.rs	Returns native Cot responses.
cot/Cargo.toml	Replaces Axum with Hyper dependencies.
cot-core/src/body.rs	Type-erases incoming request bodies.
cot-core/Cargo.toml	Removes Axum and enables Tower utilities.
Cargo.toml	Updates shared server dependencies.
Cargo.lock	Removes unused dependency entries.

_{Review effort: Balanced}

Copilot

🟡 Changes recommended

Graceful shutdown and incoming-body adaptation lack focused regression coverage.

2 open issues

2 resolved since last review

_{Review effort: Balanced}

Copilot

🔵 Needs a closer look

The replacement connection driver does not preserve HTTP upgrade support.

No open issues 🎉

2 resolved since last review

_{Review effort: Balanced}

seqre

Overall, great work! I have only few minor questions

seqre · 2026-10-19T17:05:56Z

+        B::Error: Into<Box<dyn StdError + Send + Sync>>,
+    {
+        Self::new(BodyInner::Incoming(SyncWrapper::new(
+            inner.map_err(Into::into).boxed_unsync(),


Why is boxed_unsync() needed here?

This is mostly to avoid having to tie cot_core directly to hyper. It allows for full type erasure, and while it comes with some performance cost, considering the overhead of processing HTTP requests, it's tiny. This is exactly what we used to have, because Axum does the same thing internally: https://docs.rs/axum-core/0.5.6/src/axum_core/body.rs.html#39

But technically we could directly use hyper::Incoming here. There will most likely be a negligible improvement in performance/memory usage at the downside of having to build hyper before cot_core. Considering pure hyper builds much faster than the entire axum, I think it's reasonable to take either approach.

Do you have any preferences?

seqre · 2026-10-19T17:10:18Z

                cot_core::headers::HTML_CONTENT_TYPE,
            )
-            .body(axum::body::Body::new(error_str))
+            .body(Body::fixed(error_str))


Is this unrelated fix? This could have been done earlier

This is not really an unrelated change. Previously, the error handling code used to produce axum responses directly to avoid having to do a fallible conversion between our response type and axum's. Now the body types is unified across the entire project, because hyper itself doesn't enforce any particular body type, unlike Axum. This is just a nice cleanup as a side effect of the change.

seqre · 2026-10-19T17:13:27Z

+        let handler = handler.clone();
+        let service = hyper::service::service_fn(move |request: http::Request<Incoming>| {
+            let handler = handler.clone();


Is double .clone() needed?

One is for each connection, and the other is for each request within that connection. It seems like at least the outer one (per connection) can be replaced with Arc, making this cheaper. Done in the latest commit. The inner one must stay, as the handler is FnOnce, so we need a separate instance for every call.

Double clone is what Axum is doing internally anyway, so this won't be any slower than the old version.

seqre · 2026-10-19T17:15:55Z

+    // other errors (e.g. `EMFILE` when the process has hit the limit of open
+    // files) are likely not going to go away immediately, so we wait a bit
+    // instead of spinning in a loop. This is the same strategy as used by
+    // axum.
+    error!(?error, "failed to accept connection");
+    tokio::time::sleep(Duration::from_secs(1)).await;


It doesn't have to happen now (issue for future would be enough), but this is something I'd like to be configurable

Cot only used axum for `axum::serve` and its body type, so this replaces it with a small accept loop built on hyper and hyper-util. cot_core no longer depends on axum (nor hyper) at all; incoming request bodies are stored as a type-erased `http_body::Body`. This removes axum from the critical path of a cold build, as cot_core doesn't need to wait for axum/hyper to be compiled anymore. Note that axum-core is still pulled in by tower-session. This is blocked on a tower-sessions change: maxcountryman/tower-sessions#270.

Copilot AI balanced review requested due to automatic review settings October 18, 2026 15:47

github-actions Bot added A-docs Area: Documentation A-deps Area: Dependencies C-lib Crate: cot (main library crate) C-core labels Oct 18, 2026

m4tx requested review from ElijahAhianyo and seqre and removed request for Copilot October 18, 2026 15:47

Copilot started reviewing on behalf of m4tx October 18, 2026 15:47

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m4tx added a commit to m4tx/m4txblog that referenced this pull request Oct 18, 2026

chore: test cot-rs/cot#711 (#70)

1f65264

m4tx changed the title ~~build!: remove axum dependency and use hyper directly~~ build: remove axum dependency and use hyper directly Oct 18, 2026

m4tx requested a balanced review from Copilot October 18, 2026 16:34

Copilot started reviewing on behalf of m4tx October 18, 2026 16:34

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Comment thread cot/src/project.rs

Comment thread cot/src/project.rs

m4tx force-pushed the build/remove-axum branch from 81784f3 to f171f06 Compare October 18, 2026 17:14

m4tx requested a balanced review from Copilot October 18, 2026 17:23

Copilot started reviewing on behalf of m4tx October 18, 2026 17:24

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Comment thread cot-core/src/body.rs

Comment thread cot/src/project.rs

m4tx force-pushed the build/remove-axum branch 2 times, most recently from fae8e49 to 391d76c Compare October 18, 2026 18:07

m4tx requested a balanced review from Copilot October 18, 2026 18:07

Copilot started reviewing on behalf of m4tx October 18, 2026 18:08

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seqre reviewed Oct 19, 2026

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m4tx requested a review from seqre October 19, 2026 21:47

m4tx added 2 commits October 19, 2026 23:47

address review comments

72b3c67

address review comments

1896167

m4tx force-pushed the build/remove-axum branch from b982ea9 to 1896167 Compare October 19, 2026 21:47

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m4tx commented Oct 18, 2026

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