Dependency Hijacking Library

Currently, Cargo only ships with support for dependencies that have source code available. DHL makes use of build scripts to allows linking against any dependencies, even closed source ones!

DHL works by using a local dummy crate, and then hijacking it with an arbitrary binary.

Usage

Let's use DHL to link against the private library priv:1.0.0.

Binary Setup

We start by placing the private previously compiled library. In the root of our project, we'll create a directory called libs. In that directory we'll create directories named after the triples of the targets we care about (e.g. x86_64-pc-windows-msvc). In each of those directories we'll create a directory for our rustc compiler version (e.g. rustc-1.21.0-13d94d5fa). In this directory we will place our libpriv.rlib.

Dummy Setup

Now let's create the dummy. We create a folder called priv with a Cargo.toml as follows:

[package]
name = "priv"
version = "1.0.0"
authors = [""]

Within priv, we create a src folder with an empty lib.rs file.

Injection

To setup our project Cargo.toml we need to do a few things:

Add priv as both a dependency and a build-dependency
Add dhl as a build-dependency
Configure dhl metadata to find our previously compiled
Add a build script to run dhl.

[package]
...
build = "build.rs"

[dependencies]
priv = { path = "priv" }

[build-dependencies]
priv = { path = "priv" }
dhl = "0.1.0"

[package.metadata.dhl.packages]
priv = "./libs/{{target}}/{{rustc_short_version}}/libpriv.lib"

{{target}} and {{rustc_short_version}} are by replaced during the build process via the handlebars templating engine.

As for our build script, it's pretty short:

extern crate dhl;

fn main() {
    dhl::simply_deliver();
}

And that's it. cargo build and we should be good.

Options

Package options can be configured via [package.metadata.dhl.packages]. Each package can be assigned a source directly:

priv = "./libs/{{target}}/{{rustc_short_version}}/libpriv.lib"

or with additional options:

priv = { source = "./libs/{{target}}/{{rustc_short_version}}/libpriv.lib", link = "soft" }

Sources can either be a path to a file (relative paths are based on CARGO_MANIFEST_DIR), or a url. Currently the only supported schemes are:

file
http
https