dxcontainer

Reads the part directory of a DXBC container, the file format Direct3D shader programs are stored in (Shader Model 4 to 6), and computes its digest.

let bytes = std::fs::read("shader.dxbc")?;
for part in dxcontainer::chunks(&bytes)? {
    println!("{}: {} bytes", String::from_utf8_lossy(&part.kind), part.data.len());
}
println!("digest: {:02x?}", dxcontainer::checksum(&bytes));

Run it with cargo run -p dxcontainer --example parts -- shader.dxbc; the source is examples/parts.rs. The crate documentation has a self-contained example with a hand-built container.

What it reads

A header (DXBC, a 16-byte digest, version 1, the container's size, the number of parts), the directory of the parts' offsets, then the parts one after another in the directory's order (each its four-character kind, its length and its bytes), the last ending where the container does. Shader Model 6 parts are not padded, so an offset need not be a multiple of 4. This layout holds for the 137 containers committed under dxbc-reader/tests/fixtures and dxil-reader/tests/fixtures: the tests read each to its exact end and check that checksum equals the digest it stores.

feature_flags reads the SFI0 part, the features the shader requires, as a u64 with the bytecode (SHDR/SHEX or DXIL) that says what its bits mean; feature_name names a bit the way the compiler lists it. The names were read off fxc and dxc output for programs that need one feature each (tests/fixtures/features, with the sources).

What it guarantees

The reader reads to the exact end and refuses, with an Error that names the byte, a part anywhere else (overlapping, or after a gap), a byte after the last part, a part kind twice, a size other than the container's and a version other than 1. The crate denies indexing and unchecked arithmetic at compile time, so untrusted bytes produce an Error, not a panic.

What it does not do

It does not verify the digest: the digest is not an authenticity check. checksum(bytes) computes it (MD5's block function over the bytes from 20 on, padded as the compiler pads it), for a caller that wants to compare; on all 137 committed fixtures it equals the stored digest, as it does on the 77,457 containers of five games' shipped shaders (none stores a zero digest). It interprets no part but SFI0; dxbc-reader (Shader Model 4 and 5) and dxil-reader (Shader Model 6) do.

Tests

cargo test -p dxcontainer: containers built by hand for each refusal, every truncation of one, and the committed fixtures of dxbc-reader and dxil-reader read to their end. No game files are needed.

License: GPL-3.0-or-later.