cdm-host

A native Rust host for the system Widevine CDM (libwidevinecdm.so). It loads the CDM that ships with Chrome/Brave (or any Chromium-family app) and drives it through its official cdm::ContentDecryptionModule interface to:

• generate a license challenge,
• accept a license response (loading the content keys), and
• decrypt CENC buffers.

No keys are extracted — the CDM keeps its device key sealed and does the work internally, exactly as a browser does. This is service-agnostic: any Widevine service (Spotify web, Apple Music web, …) is just a thin auth + manifest layer on top.

Usage

use cdm_host::CdmHost;

// Either point at a CDM yourself…
let cdm = CdmHost::open("/path/to/libwidevinecdm.so")?;

// …or have one ensured under a directory you choose (copied from an installed
// browser, or — with the `download` feature — fetched from Google):
let cdm = CdmHost::install_or_open("~/.cache/myapp/widevine")?;

let challenge = cdm.challenge(&pssh_box)?;   // → send to the license server
cdm.update(&license_response)?;              // ← keys loaded
let clear = cdm.decrypt(&sample, &kid, &iv, &subsamples)?;

The CDM binary is never shipped

libwidevinecdm.so is Google's proprietary, non-redistributable binary, so this crate doesn't bundle it. [vendor] sources it at runtime the same way Chrome/Brave/Spotify do — by locating an existing copy, or downloading one:

• [CdmHost::open] — you supply the path.
• [CdmHost::install_or_open] — ensure it under your dir: existing copy → copy from a detected local CDM (Brave/Chrome/Chromium/Spotify/Discord) → (feature download) extract it from the official Google Chrome package.

Build — no C++ compiler needed on supported targets

shim.cc implements cdm::Host_11 (compiled against the vendored Chromium content_decryption_module.h, so the vtable is correct-by-construction). build.rs links a prebuilt static shim (prebuilt/<target>/libcdmshim.a) when one is shipped for the target — no compiler required (only the ubiquitous libstdc++ runtime). Targets without a prebuilt fall back to compiling shim.cc via cc, which needs g++/clang++.

• prebuilt target → no compiler, .h/.cc unused.
• other target → needs a C++ compiler + the vendored header (BSD, from chromium.googlesource.com/chromium/cdm).

Regenerate a prebuilt:

g++ -std=c++14 -fPIC -Ivendor -c shim.cc -o shim.o
ar rcs prebuilt/<target-triple>/libcdmshim.a shim.o

Cargo features

• download — enable the Google-Chrome-package fallback in install_or_open (pulls ureq + pure-Rust lzma-rs/ruzstd/tar for extraction). Off by default to keep the base crate light.

Standalone

This crate has no Spotify (or any service) code; it's consumed as a git/crates.io dependency.