Introduction

At compile time, writes attributes such as the git revision, whether the working directory is clean, git status, build time, etc to a generated file. This is then available to the binary, for example in the version information.

Due to the integration with git itself, albeit in a simple way, it is hard for me to include an example of how to use it in this repository. Instead, I refer to https://github.com/calmofthestorm/eseb as a simple binary which uses this.

The short of it is that you need to add build_stamp to both dependencies and build-dependencies in Cargo.toml as so:

[dependencies]
build_stamp = "1"

[build-dependencies]
build_stamp = "1"

and then add the following include for the generated code to lib.rs, main.rs, or a submodule thereof:

include!(concat!(env!("OUT_DIR"), "/generated_stamp.rs"));

You can then access the BUILD_STAMP constant. The below example is using clap to define a command-line interface that includes build information in the version:

let matches = App::new("eseb")
    .name(env!("CARGO_PKG_NAME"))
    .author(env!("CARGO_PKG_AUTHORS"))
    .version(format!("{} ({})", env!("CARGO_PKG_VERSION"), BUILD_STAMP.git_revision_cleanness()).as_ref())

Limitations

Be aware that Cargo may not always run build.sh when you might like. For example, after you commit, you would expect that if your working directory is clean, a build would be tagged as clean. If you haven't changed any files, however, Cargo will continue to use the previously generated stamp.

You can fix this by touching build.rs manually, or using the (included) post commit hook. There may be other similar edge cases I haven't thought of.

Security

I don't recommend relying on something this basic for any sensitive application, such as anything related to attestation or integrity verification. My purpose in creating this is simply to have a better understanding of my own binaries that are here and there when there is an error or similar. As such, "probably approximately good enough" is good enough for me:-)