Explore a Rust interface for CCF applications

[Amaury Chamayou (achamayou)]

Summary

This draft explores what it would take to support native CCF applications written in Rust while keeping the integration boundary small and explicit.

It introduces:

• a C ABI bridge between the CCF host and Rust application code;
• an initial ccf-app Rust crate for endpoint registration, request and response handling, authentication selection, and raw-byte KV access;
• CMake support for building and packaging Rust applications alongside native CCF applications;
• a basic Rust records application, end-to-end test coverage, and user documentation.

Goal

The goal is to evaluate the viability and ergonomics of Rust as another native CCF application language without exposing C++ implementation details across the boundary. The proposed API deliberately starts small so that ownership, lifetime, panic containment, transaction, concurrency, and packaging concerns can be reviewed before expanding the surface area.

Exploration status

This is exploratory work, not a commitment to a stable or production-supported Rust SDK. The current interface intentionally omits advanced endpoint configuration, custom authentication policies, historical queries, indexing, and commit callbacks. Feedback is especially welcome on the ABI design, safety guarantees, SDK ergonomics, and long-term maintenance implications.

This replays the work from achamayou/CCF#107 onto the current microsoft/CCF main branch so it can be discussed and evaluated in the upstream repository.

[Copilot]

Pull request overview

Introduces exploratory Rust support for native CCF applications through a C ABI bridge and Rust SDK.

Changes:

• Adds endpoint, authentication, response, and raw KV APIs.
• Adds Cargo/CMake integration and packaging.
• Adds a sample application, E2E coverage, documentation, and changelog entry.

Custom instructions used

• .github/copilot-instructions.md
• .github/instructions/changelog.instructions.md
• .github/instructions/reviewing.instructions.md

Reviewed changes

Copilot reviewed 17 out of 19 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
CHANGELOG.md	Announces Rust application support.
CMakeLists.txt	Installs Rust sources and registers the E2E test.
cmake/ccf_app.cmake	Adds the Rust application build helper.
cmake/gersemi_definitions.cmake	Registers the helper for CMake formatting.
include/ccf/rust_ffi.h	Defines the public C ABI.
src/rust/app_bridge.cpp	Implements the C++ bridge and endpoint registry.
src/rust/ccf-app/Cargo.toml	Defines the Rust SDK crate.
src/rust/ccf-app/Cargo.lock	Locks the SDK crate.
src/rust/ccf-app/src/lib.rs	Implements the Rust-facing API and handlers.
samples/CMakeLists.txt	Includes the Rust sample.
samples/apps/basic_rust/CMakeLists.txt	Builds the sample application.
samples/apps/basic_rust/Cargo.toml	Defines the sample crate.
samples/apps/basic_rust/Cargo.lock	Locks sample dependencies.
samples/apps/basic_rust/rust-toolchain.toml	Pins Rust 1.90.
samples/apps/basic_rust/src/lib.rs	Implements records and health endpoints.
tests/basic_rust.py	Exercises authentication and KV behavior.
doc/build_apps/index.rst	Adds Rust to the application overview.
doc/build_apps/get_started.rst	Links Rust build guidance.
doc/build_apps/example_rust.rst	Documents the initial Rust interface.

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[Copilot]

Pull request overview

Copilot reviewed 20 out of 22 changed files in this pull request and generated 5 comments.

[Amaury Chamayou (achamayou)]

Copilot resolve the merge conflicts in this pull request

[Copilot]

Copilot resolve the merge conflicts in this pull request

Resolved: merged the branch with origin/main and fixed the CHANGELOG.md conflict by keeping both the Rust-app addition and the C++23 requirement note under the 7.0.14 section.