conduit/docs/development.md

Development

Information about developing the project. If you are only interested in using it, you can safely ignore this page. If you plan on contributing, see the contributor's guide.

conduwuit project layout

conduwuit uses a collection of sub-crates, packages, or workspace members that indicate what each general area of code is for. All of the workspace members are under src/. The workspace definition is at the top level / root Cargo.toml.

The crate names are generally self-explanatory:

• admin is the admin room
• api is the HTTP API, Matrix C-S and S-S endpoints, etc
• core is core conduwuit functionality like config loading, error definitions, global utilities, logging infrastructure, etc
• database is RocksDB methods, helpers, RocksDB config, and general database definitions, utilities, or functions
• macros are conduwuit Rust macros like general helper macros, logging and error handling macros, and syn and procedural macros used for admin room commands and others
• main is the "primary" sub-crate. This is where the main() function lives, tokio worker and async initialisation, Sentry initialisation, clap init, and signal handling. If you are adding new Rust features, they must go here.
• router is the webserver and request handling bits, using axum, tower, tower-http, hyper, etc, and the global server state to access services.
• service is the high-level database definitions and functions for data, outbound/sending code, and other business logic such as media fetching.

It is highly unlikely you will ever need to add a new workspace member, but if you truly find yourself needing to, we recommend reaching out to us in the Matrix room for discussions about it beforehand.

The primary inspiration for this design was apart of hot reloadable development, to support "conduwuit as a library" where specific parts can simply be swapped out. There is evidence Conduit wanted to go this route too as axum is technically an optional feature in Conduit, and can be compiled without the binary or axum library for handling inbound web requests; but it was never completed or worked.

See the Rust documentation on Workspaces for general questions and information on Cargo workspaces.

Adding compile-time features

If you'd like to add a compile-time feature, you must first define it in the main workspace crate located in src/main/Cargo.toml. The feature must enable a feature in the other workspace crate(s) you intend to use it in. Then the said workspace crate(s) must define the feature there in its Cargo.toml.

So, if this is adding a feature to the API such as woof, you define the feature in the api crate's Cargo.toml as woof = []. The feature definition in main's Cargo.toml will be woof = ["conduit-api/woof"].

The rationale for this is due to Rust / Cargo not supporting "workspace level features", we must make a choice of; either scattering features all over the workspace crates, making it difficult for anyone to add or remove default features; or define all the features in one central workspace crate that propagate down/up to the other workspace crates. It is a Cargo pitfall, and we'd like to see better developer UX in Rust's Workspaces.

Additionally, the definition of one single place makes "feature collection" in our Nix flake a million times easier instead of collecting and deduping them all from searching in all the workspace crates' Cargo.tomls. Though we wouldn't need to do this if Rust supported workspace-level features to begin with.

List of forked dependencies

During conduwuit development, we have had to fork some dependencies to support our use-cases in some areas. This ranges from things said upstream project won't accept for any reason, faster-paced development (unresponsive or slow upstream), conduwuit-specific usecases, or lack of time to upstream some things.

• ruma/ruma: https://github.com/girlbossceo/ruwuma - various performance improvements, more features, faster-paced development, client/server interop hacks upstream won't accept, etc
• facebook/rocksdb: https://github.com/girlbossceo/rocksdb - liburing build fixes, GCC build fix, and logging callback C API for Rust tracing integration
• tikv/jemallocator: https://github.com/girlbossceo/jemallocator - musl builds seem to be broken on upstream
• zyansheep/rustyline-async: https://github.com/girlbossceo/rustyline-async - tab completion callback and CTRL+\ signal quit event for CLI
• rust-rocksdb/rust-rocksdb: https://github.com/girlbossceo/rust-rocksdb-zaidoon1 - @zaidoon1's fork has quicker updates, more up to date dependencies. Our changes fix musl build issues, Rust part of the logging callback C API, removes unnecessary gtest include, and uses our RocksDB and jemallocator
• tokio-rs/tracing: https://github.com/girlbossceo/tracing - Implements Clone for EnvFilter to support dynamically changing tracing envfilter's alongside other logging/metrics things

Debugging with tokio-console

tokio-console can be a useful tool for debugging and profiling. To make a tokio-console-enabled build of conduwuit, enable the tokio_console feature, disable the default release_max_log_level feature, and set the --cfg tokio_unstable flag to enable experimental tokio APIs. A build might look like this:

RUSTFLAGS="--cfg tokio_unstable" cargo build \
    --release \
    --no-default-features \
    --features=systemd,element_hacks,gzip_compression,brotli_compression,zstd_compression,tokio_console