refactor!: extract framework core to cot-core #444

seqre · 2026-01-11T18:49:09Z

This PR attempts to extract the core functionality of the framework to separate crate to speed up compilation among other reasons.

The modules fully/partially moved:

basic Cot types
body
error
headers
html
json
response
request
middleware
handler

I think moving router would be valid move as well, but in the current format it's too intertwined with OpenAPI functionality (that we don't want to pull into core) that it can be done at a later time.

With cot-core being a separate crate, the following items had to become public:

cot_core::error::backtrace - needed for ErrorPage
cot_core::error::error_impl::* - to allow implementing of errors in cot
Error.backtrace() - needed for supplying error backtrace in ErrorPageTemplateBuilder
Backtrace.frames() - needed for the Template derive for ErrorPageTemplate (used in error.html template)
StackFrame.symbol_name() - as above
StackFrame.location() - as above
StackFrame - as above
Body.axum() - needed for request_axum_to_cot in project.rs
InvalidContentType
AppName
RouteName
BoxRequestHandler - used in openapi.rs and router.rs
into_box_request_handler - used in method.rs and router.rs

Stayed private with following gotchas:

NotFound.router() - removed deprecated NotFound constructor methods from Error

seqre · 2026-01-12T18:26:59Z

The nightly error should be fixed by rust-lang/rust#150939

m4tx

Looks nice, and seems like it lays a solid foundation for our eventual extraction of the ORM to a separate crate!

I've tried to generate the docs with just docs and it seems like there's a ton of warnings coming from cot-core (outside of missing examples, which are expected) - please make sure these are fixed before we consider merging this.

cot-core/src/handler.rs

cot-core/src/lib.rs

cot/src/error_page.rs

codecov · 2026-01-16T18:59:30Z

Codecov Report

❌ Patch coverage is 93.63296% with 17 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cot-core/src/request/extractors.rs	94.11%	3 Missing and 4 partials ⚠️
cot-core/src/middleware.rs	85.71%	6 Missing ⚠️
cot/src/request/extractors.rs	86.66%	2 Missing ⚠️
cot-core/src/request.rs	98.21%	0 Missing and 1 partial ⚠️
cot/src/error_page.rs	0.00%	1 Missing ⚠️

Flag	Coverage Δ
rust	`90.37% <93.63%> (-0.01%)`	⬇️

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

Files with missing lines	Coverage Δ
cot-core/src/body.rs	`84.89% <100.00%> (ø)`
cot-core/src/error/backtrace.rs	`96.82% <100.00%> (ø)`
cot-core/src/error/error_impl.rs	`90.13% <100.00%> (ø)`
cot-core/src/error/method_not_allowed.rs	`100.00% <ø> (ø)`
cot-core/src/error/uncaught_panic.rs	`75.00% <ø> (ø)`
cot-core/src/handler.rs	`78.26% <100.00%> (ø)`
cot-core/src/html.rs	`97.44% <ø> (ø)`
cot-core/src/request/path_params_deserializer.rs	`63.49% <ø> (ø)`
cot-core/src/response.rs	`97.50% <ø> (ø)`
cot-core/src/response/into_response.rs	`99.27% <100.00%> (ø)`
... and 26 more

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# Conflicts: # Cargo.toml

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m4tx

Looks amazing - in the thorough review, I found a few documentation issues; when you fix them, please feel free to merge this!

m4tx · 2026-01-25T23:37:35Z

cot-core/src/request/extractors.rs

+/// Extractors implementing this trait are used in route handlers that consume
+/// the request body and therefore can only be used once per request.
+///
+/// See [`crate::request::extractors`] documentation for more information about


This redirects to cot_core docs instead of cot.

m4tx · 2026-01-25T23:39:23Z

cot/src/request/extractors.rs

-impl_into_cot_error!(JsonDeserializeError, BAD_REQUEST);
-
 /// An extractor that gets the request body as form data and deserializes it
 /// into a type `F` implementing `cot::form::Form`.


This hasn't changed in your change, but while we're at it, please make cot::form::Form an actual link.

m4tx · 2026-01-25T23:39:55Z

cot-core/src/request/extractors.rs

+///
+/// If you need to consume the body of the request, use [`FromRequest`] instead.
+///
+/// See [`crate::request::extractors`] documentation for more information about


This redirects to cot_core docs instead of cot.

m4tx · 2026-01-25T23:47:43Z

cot/src/error_page.rs

        if let Some(not_found) = error.inner().downcast_ref::<NotFound>() {
            use crate::error::NotFoundKind as Kind;
            match &not_found.kind {
-                Kind::FromRouter => {}


Please add this match variant back for clarity, or at least explicitly document that we don't do anything in case we get FromRouter here.

m4tx · 2026-01-25T23:48:49Z

cot/src/error.rs

+#[doc(inline)]
+pub use cot_core::error::{MethodNotAllowed, UncaughtPanic};
+#[doc(inline)]
+pub(crate) use cot_core::error::{backtrace, impl_into_cot_error};


If it's pub(crate) anyway, what's the point in re-exporting this? Can't we use cot_core directly instead?

m4tx · 2026-01-26T00:00:07Z

cot-core/src/request.rs

+//!
+//! Cot uses the [`Request`](http::Request) type from the [`http`] crate
+//! to represent incoming HTTP requests. However, it also provides a
+//! [`RequestExt`](../../cot/request/trait.RequestExt.html) trait that contain
+//! various helper methods for working with HTTP requests. These methods are
+//! used to access the application context, project configuration, path
+//! parameters, and more. You probably want to have a `use` statement for
+//! [`RequestExt`](../../cot/request/trait.RequestExt.html) in your code most of
+//! the time to be able to use these functions:
+//!
+//! ```
+//! use cot::request::RequestExt;
+//! ```


I think we can now remove this, as there's a copy of this in the main crate (and if we don't remove it here, it will inevitably go out of sync eventually).

m4tx · 2026-01-26T00:00:38Z

cot-core/src/response.rs

 //!
 //! Cot uses the [`Response`](http::Response) type from the [`http`] crate
 //! to represent outgoing HTTP responses. However, it also provides a
 //! [`ResponseExt`] trait that contain various helper methods for working with
 //! HTTP responses. These methods are used to create new responses with HTML
 //! content types, redirects, and more. You probably want to have a `use`
 //! statement for [`ResponseExt`] in your code most of the time to be able to
 //! use these functions:
 //!
 //! ```
 //! use cot::response::ResponseExt;
 //! ```


Same here - we can remove this.

m4tx · 2026-01-26T00:03:45Z

cot-core/src/request/extractors.rs

+/// An extractor that extracts data from the URL params.
+///
+/// The extractor is generic over a type that implements
+/// `serde::de::DeserializeOwned`.


Suggested change

/// `serde::de::DeserializeOwned`.

/// [`serde::de::DeserializeOwned`].

I know you didn't change this, but it's a good opportunity to make this better.

m4tx · 2026-01-26T00:03:56Z

cot-core/src/request/extractors.rs

+/// An extractor that extracts data from the URL query parameters.
+///
+/// The extractor is generic over a type that implements
+/// `serde::de::DeserializeOwned`.


Suggested change

/// `serde::de::DeserializeOwned`.

/// [`serde::de::DeserializeOwned`].

m4tx · 2026-01-26T00:04:04Z

cot-core/src/request/extractors.rs

+impl_into_cot_error!(QueryParametersParseError, BAD_REQUEST);
+
+/// Extractor that gets the request body as JSON and deserializes it into a type
+/// `T` implementing `serde::de::DeserializeOwned`.


Suggested change

/// `T` implementing `serde::de::DeserializeOwned`.

/// `T` implementing [`serde::de::DeserializeOwned`].

m4tx · 2026-01-26T00:14:25Z

By the way, asking out of curiosity - did you try to find out why the semver-checks is complaining? Seems like it produces a lot of false positives about modules/structures not accessible using old paths, which isn't true. I'm wondering if anyone has reported that yet (and if not, it's definitely worth reporting!)

EDIT: ah, I guess this is obi1kenobi/cargo-semver-checks#638

github-actions bot added the C-lib Crate: cot (main library crate) label Jan 11, 2026

seqre mentioned this pull request Jan 11, 2026

refactor!: extract framework core to cot-core #403

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seqre and others added 18 commits January 22, 2026 23:39

create new crate

3c67ad5

# Conflicts: # Cargo.toml

add basic types

ede952b

move error

dc9a3c9

move body

7dd95c4

move headers

d9c96db

move html

f7b1f27

move json

b4069e8

move response

d5b74a2

move request

afd5ceb

move middleware

d84948d

move handler

0c87698

fixes

0c36ac4

add body docs

818e881

remove no longer needed marker

dd3c37a

fix the build

b1f9dc7

hide private items

03595ce

upstream docs

f0bb420

rebase fixes

cb940a3

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	/// `serde::de::DeserializeOwned`.
	/// [`serde::de::DeserializeOwned`].

	/// `T` implementing `serde::de::DeserializeOwned`.
	/// `T` implementing [`serde::de::DeserializeOwned`].

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