Emboss

Macros to embed metadata as an ELF/Mach-O section in your final binary.

Pairs quite nicely with vergen.

Quickstart

Include emboss in your Cargo.toml:

[package]
# <snip>

[dependencies]
emboss = "0.5.1"

Import the emboss macro and call it with the key and value you want to embed:

use emboss::emboss;

emboss!(key = "my-custom-value", value = "1");

Run a quick cargo build and then examine the resulting binary:

$ strings target/debug/kana | grep my-custom-value
my-custom-value=1

You can also parse this yourself from the binary or use rsps to fetch it from a running process.

Detailed Usage

Emboss Many

You can emboss multiple key value pairs at once using emboss_many:

use emboss::emboss_many;

// The `items` property takes an array of key-value structs
emboss_many!(items = [
    { key = "foo", value = "1" },
    { key = "bar", value = "2" }
]);

Emboss From Environment Variables

If you need to pull the value of a environment variable for the embossing, there is emboss_env:

use emboss::emboss_env;

// `env_var` will be the environment variable to evaluate at compile time
// `key` will be the key in the embossing, same as it is in the normal emboss macro
// If you omit `key`, it'll reuse the env var as the `key`
emboss_env!(env_var = "FOO_VAR", key = "foo");

If the environment variable is not present at compile time, the macro will fail. You can change this behavior with the fallback property:

use emboss::emboss_env;

// The `Fail` variant is the default behavior, blowing up when the `env_var` is missing  
emboss_env!(env_var = "DOES_NOT_EXIST", fallback = Fail);

// The `Empty` variant will use an empty value when the `env_var` is missing  
emboss_env!(env_var = "DOES_NOT_EXIST", fallback = Empty);

// The `Value` variant will use a specific, user-specified value when the `env_var` is missing
emboss_env!(env_var = "DOES_NOT_EXIST", fallback = Value("1"));

Emboss Many From Environment Variables

Similar to emboss_many, but for values pulled from environment variables. You can use all the same properties present in emboss_env:

use emboss::emboss_envs;

// The `env_vars` property takes an array of environment variable spec structs
emboss_envs!(env_vars = [
    { env_var = "FOO_VAR" },
    { env_var = "BAR_VAR", key = "bar", fallback = Empty },
    { env_var = "BAZ_VAR", key = "baz", fallback = Value("3") },
]);

Exports and Enum Variants

All emboss macros support the export_name parameter, which creates a module with a public API for accessing embossed data:

use emboss::emboss;

emboss!(
    key = "app-version", 
    value = "1.0.0", 
    export_name = "version_info"
);

// Later in your code:
let (_, version) = version_info::EMBOSSED.get_by_key("app-version").unwrap();
println!("App version: {}", version);

You can also customize enum variant names for better ergonomics:

use emboss::emboss_many;

emboss_many!(
    items = [
        { key = "version", value = "1.0.0", variant_name = "Version" },
        { key = "build-id", value = "abc123", variant_name = "BuildId" }
    ],
    export_name = "app_info"
);

// Access via enum variants
let (_, version) = app_info::EMBOSSED.get_by_kind(app_info::EmbossedKeyKind::Version);
let (_, build_id) = app_info::EMBOSSED.get_by_kind(app_info::EmbossedKeyKind::BuildId);

Extended Arguments

All emboss macros support the following properties:

• stored_in: The name of the section to store embossed data. Defaults to .emboss.meta.

On macOS, an additional segment parameter allows you to customize the segment that the section is placed in:

emboss!(
    key = "macos-version", 
    value = "14.0", 
    segment = "__DATA", 
    stored_in = "__custom_section"
);

By default, the segment will be __DATA.

Reading Embossed Data

We provide helper functions to retrieve embossed data from a given sequence of bytes.

Here is an example using the object crate:

use emboss::extract;

fn read_binary_metadata(file: &object::File) {
  // Pull the raw data from the metadata section of the binary
  let section = file.section_by_name(emboss_common::DEFAULT_SECTION_NAME)
      .expect("metadata should exist");
  let data = section.data().expect("data should be available");
  
  // Parse the embossed data
  let metadata = extract::extract_metadata_into_hashmap(data)
      .expect("should be able to parse metadata");

  // Access values by key
  let version = metadata.get("version").expect("version should be present");
  println!("Version: {}", version);
  
  // Alternatively, get as a vector of pairs
  let pairs = extract::extract_metadata_into_vec(data)
      .expect("should be able to parse metadata");
  
  for (key, value) in pairs {
      println!("{}: {}", key, value);
  }
}

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.