Crate relay_cabi

source ·
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This package contains the C-ABI of Relay. It builds a C header file and associated library that can be linked to any C or C++ program. Note that the header is C only. Primarily, this package is meant to be consumed by higher-level wrappers in other languages, such as the sentry-relay Python package.


Building the dynamic library has the same requirements as building the relay crate:

  • Latest stable Rust and Cargo
  • A checkout of this repository and all its GIT submodules

To build, run make release in this directory. This creates a release build of the dynamic library in target/release/librelay_cabi.*.


The header comes packaged in the include/ directory. It does not have any dependencies other than standard C headers. Then, include it in sources and use like this:

#include "relay.h"

int main() {
    RelayUuid uuid = relay_generate_relay_id();
    // use uuid

    return 0;

In your application, point to the Relay include directory and specify the relay library:

$(CC) -Irelay-cabi/include -Ltarget/release -lrelay -o myprogram main.c



In addition to the build requirements, development requires a recent version of the the cbindgen tool. To set this up, run:

cargo install cbindgen

If your machine already has cbindgen installed, check the header of [include/relay.h] for the minimum version required. This can be verified by running cbindgen --version. It is generally advisable to keep cbindgen updated to its latest version, and always check in cbindgen updates separate from changes to the public interface.


This package contains the Rust crate relay-cabi that exposes a public FFI interface. There are additional build steps involved in generating the header file located at include/relay.h. To aid development, there is a Makefile that exposes all relevant commands for building:

  • make build: Builds the library using cargo.
  • make header: Updates the header file based on the public interface.
  • make clean: Removes all build artifacts but leaves the header.
  • make: Builds the library and the header.

For ease of development, the header is always checked into the repository. After making changes, do not forget to run at least make header to ensure the header is in sync with the library.

Development Flow

  1. Make changes to the relay crates and add tests.
  2. Update relay-cabi and add, remove or update functions as needed.
  3. Regenerate the header by running make header in the relay-cabi/ directory.
  4. Go to the Python package in the py/ folder and update the high-level wrappers.
  5. Consider whether this changeset requires a major version bump.

The general rule for major versions is:

  • If everything is backward compatible, do not major bump.
  • If the C interface breaks compatibility but high-level wrappers are still backwards compatible, do not major bump. The C interface is currently viewed as an implementation detail.
  • If high-level wrappers are no longer backwards compatible or there are breaking changes in the relay crate itself, do major bump.