subc-daemon 0.22.1

use std::path::{Path, PathBuf};
use std::process::Command;

fn main() {
    println!("cargo:rustc-check-cfg=cfg(loom)");
    if std::env::var_os("CARGO_FEATURE_LOOM").is_some() {
        // Scope loom instrumentation to subc-daemon. A workspace-wide `RUSTFLAGS=--cfg loom`
        // also disables Tokio's net/process modules, so it cannot compile this daemon crate.
        println!("cargo:rustc-cfg=loom");
    }

    // Build provenance, embedded so a deployed daemon and a CLI can DISAGREE.
    //
    // The crate version cannot discriminate a skewed pair: it moves on release,
    // not on commit, so a daemon and a `ck` separated by nine wire-touching
    // commits both report the same version and the comparison agrees exactly
    // when it matters. The git commit moves per change and the Cargo.lock
    // digest moves per dependency change; together they answer "which source"
    // and "which dependency set". Neither alone suffices: a lock digest misses
    // source-only wire changes, a commit SHA misses a rebuild against edited
    // dependencies.
    //
    // Failure reports "unavailable", never a placeholder value: a placeholder
    // would compare EQUAL between two broken builds, which reads as a verified
    // match precisely when nothing was verified.
    println!(
        "cargo:rustc-env=SUBC_BUILD_GIT_SHA={}",
        git_head_sha().unwrap_or_else(|| "unavailable".to_string())
    );
    println!(
        "cargo:rustc-env=SUBC_BUILD_LOCK_DIGEST={}",
        lock_digest().unwrap_or_else(|| "unavailable".to_string())
    );
}

fn git_head_sha() -> Option<String> {
    let manifest_dir = std::env::var("CARGO_MANIFEST_DIR").ok()?;
    // Rebuild when HEAD moves. Best-effort: if the paths are missing (a source
    // tarball), the SHA reports unavailable and there is nothing to track.
    let git_dir = Path::new(&manifest_dir).join("../../.git");
    if git_dir.exists() {
        println!("cargo:rerun-if-changed={}", git_dir.join("HEAD").display());
        // Branch tips move under refs/heads without HEAD itself changing.
        println!("cargo:rerun-if-changed={}", git_dir.join("refs").display());
    }
    let output = Command::new("git")
        .args(["rev-parse", "HEAD"])
        .current_dir(&manifest_dir)
        .output()
        .ok()?;
    if !output.status.success() {
        return None;
    }
    let sha = String::from_utf8(output.stdout).ok()?.trim().to_string();
    // Reject output that is not a 40-character hexadecimal commit SHA.
    if sha.len() != 40 || !sha.bytes().all(|b| b.is_ascii_hexdigit()) {
        return None;
    }
    // A build from a dirty tree embeds HEAD while running different code --
    // the repository-vs-process lie this field exists to catch, one level
    // down. Mark it so two dirty builds never read as a verified match. If
    // the dirtiness probe itself fails, the whole identity reports
    // unavailable rather than an unmarked SHA that may be lying.
    let status = Command::new("git")
        .args(["status", "--porcelain"])
        .current_dir(&manifest_dir)
        .output()
        .ok()?;
    if !status.status.success() {
        return None;
    }
    if status.stdout.is_empty() {
        Some(sha)
    } else {
        Some(format!("{sha}-dirty"))
    }
}

fn lock_digest() -> Option<String> {
    let manifest_dir = std::env::var("CARGO_MANIFEST_DIR").ok()?;
    let lock_path = PathBuf::from(&manifest_dir).join("../../Cargo.lock");
    println!("cargo:rerun-if-changed={}", lock_path.display());
    let bytes = std::fs::read(&lock_path).ok()?;
    Some(sha256_hex(&bytes))
}

/// SHA-256, hand-rolled (FIPS 180-4).
///
/// Deliberately not a crate dependency: this digest EXISTS to describe
/// Cargo.lock, and pulling a hashing crate through that same lock would make
/// the instrument a function of the thing it measures. ~40 lines buys
/// independence from its own subject.
fn sha256_hex(data: &[u8]) -> String {
    const K: [u32; 64] = [
        0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4,
        0xab1c5ed5, 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe,
        0x9bdc06a7, 0xc19bf174, 0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f,
        0x4a7484aa, 0x5cb0a9dc, 0x76f988da, 0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
        0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc,
        0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85, 0xa2bfe8a1, 0xa81a664b,
        0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070, 0x19a4c116,
        0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
        0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7,
        0xc67178f2,
    ];
    let mut h: [u32; 8] = [
        0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab,
        0x5be0cd19,
    ];
    let mut message = data.to_vec();
    let bit_len = (data.len() as u64) * 8;
    message.push(0x80);
    while message.len() % 64 != 56 {
        message.push(0);
    }
    message.extend_from_slice(&bit_len.to_be_bytes());

    // `chunks_exact` over `as_chunks`: this build script must compile on the
    // oldest toolchain the workspace supports, and `[T]::as_chunks` is newer
    // than that floor. The lint arrived with a toolchain update; the code is
    // correct either way.
    #[allow(unknown_lints, clippy::chunks_exact_to_as_chunks)]
    for chunk in message.chunks_exact(64) {
        let mut w = [0u32; 64];
        #[allow(unknown_lints, clippy::chunks_exact_to_as_chunks)]
        for (i, word) in chunk.chunks_exact(4).enumerate() {
            w[i] = u32::from_be_bytes([word[0], word[1], word[2], word[3]]);
        }
        for i in 16..64 {
            let s0 = w[i - 15].rotate_right(7) ^ w[i - 15].rotate_right(18) ^ (w[i - 15] >> 3);
            let s1 = w[i - 2].rotate_right(17) ^ w[i - 2].rotate_right(19) ^ (w[i - 2] >> 10);
            w[i] = w[i - 16]
                .wrapping_add(s0)
                .wrapping_add(w[i - 7])
                .wrapping_add(s1);
        }
        let (mut a, mut b, mut c, mut d, mut e, mut f, mut g, mut hh) =
            (h[0], h[1], h[2], h[3], h[4], h[5], h[6], h[7]);
        for i in 0..64 {
            let s1 = e.rotate_right(6) ^ e.rotate_right(11) ^ e.rotate_right(25);
            let ch = (e & f) ^ (!e & g);
            let temp1 = hh
                .wrapping_add(s1)
                .wrapping_add(ch)
                .wrapping_add(K[i])
                .wrapping_add(w[i]);
            let s0 = a.rotate_right(2) ^ a.rotate_right(13) ^ a.rotate_right(22);
            let maj = (a & b) ^ (a & c) ^ (b & c);
            let temp2 = s0.wrapping_add(maj);
            hh = g;
            g = f;
            f = e;
            e = d.wrapping_add(temp1);
            d = c;
            c = b;
            b = a;
            a = temp1.wrapping_add(temp2);
        }
        h[0] = h[0].wrapping_add(a);
        h[1] = h[1].wrapping_add(b);
        h[2] = h[2].wrapping_add(c);
        h[3] = h[3].wrapping_add(d);
        h[4] = h[4].wrapping_add(e);
        h[5] = h[5].wrapping_add(f);
        h[6] = h[6].wrapping_add(g);
        h[7] = h[7].wrapping_add(hh);
    }
    h.iter().map(|word| format!("{word:08x}")).collect()
}