build.rs

// Build script for ACBU Smart Contracts
// Verifies WASM artifact integrity before compilation.
// Fails fast if hash mismatches to prevent supply chain attacks.
//
// The WASM file is NOT stored in git — only its SHA-256 hash is pinned
// in source (inside each contractimport! macro and in this script).
// Run  ./scripts/fetch_token_wasm.sh  to download the artifact before
// your first build.

use std::fs;
use std::path::Path;
use std::process;

/// Expected SHA-256 of soroban_token_contract.wasm.
/// Must match the sha256 field in every contractimport! that references
/// this artifact (acbu_minting, acbu_burning, acbu_reserve_tracker).
const EXPECTED_HASH: &str =
    "6b14997b915dee21082884cd5a2f1f2f0aef0073d1dcb9c5b3c674cf487fb41d";

const WASM_PATH: &str = "soroban_token_contract.wasm";

fn main() {
    // Re-run this script only when the WASM file itself changes.
    println!("cargo:rerun-if-changed={}", WASM_PATH);

    if !Path::new(WASM_PATH).exists() {
        eprintln!("error[build]: {} not found.", WASM_PATH);
        eprintln!();
        eprintln!("  The WASM artifact is not stored in the repository.");
        eprintln!("  Run the fetch script to download it before building:");
        eprintln!();
        eprintln!("      ./scripts/fetch_token_wasm.sh");
        eprintln!();
        eprintln!("  Expected SHA-256: {}", EXPECTED_HASH);
        process::exit(1);
    }

    let data = fs::read(WASM_PATH).unwrap_or_else(|e| {
        eprintln!("error[build]: Cannot read {}: {}", WASM_PATH, e);
        process::exit(1);
    });

    let actual_hash = sha256_hex(&data);
    if actual_hash != EXPECTED_HASH {
        eprintln!("error[build]: WASM hash mismatch — possible supply-chain tampering.");
        eprintln!("  expected: {}", EXPECTED_HASH);
        eprintln!("  actual:   {}", actual_hash);
        eprintln!();
        eprintln!("  Re-run ./scripts/fetch_token_wasm.sh to restore the verified artifact.");
        process::exit(1);
    }

    println!(
        "cargo:warning=soroban_token_contract.wasm verified ({} bytes, sha256 OK)",
        data.len()
    );

    verify_source_hashes();
}

/// Verify that every contractimport! in source still references the expected hash.
fn verify_source_hashes() {
    let tagged_files = [
        "acbu_minting/src/lib.rs",
        "acbu_burning/src/lib.rs",
        "acbu_reserve_tracker/src/lib.rs",
    ];

    for path in &tagged_files {
        println!("cargo:rerun-if-changed={}", path);
        match fs::read_to_string(path) {
            Ok(content) => {
                if content.contains("contractimport!")
                    && !content.contains(&format!("sha256 = \"{}\"", EXPECTED_HASH))
                {
                    eprintln!(
                        "error[build]: {} contains a contractimport! \
                         with a hash that does not match EXPECTED_HASH.",
                        path
                    );
                    eprintln!("  expected: {}", EXPECTED_HASH);
                    eprintln!("  Update the sha256 field in that file to match.");
                    process::exit(1);
                }
            }
            Err(e) => {
                eprintln!("cargo:warning=Could not read {} for hash check: {}", path, e);
            }
        }
    }
}

/// Compute a lowercase hex SHA-256 digest without any external crate.
fn sha256_hex(data: &[u8]) -> String {
    // Initial hash values (first 32 bits of fractional parts of square roots
    // of the first 8 primes).
    let mut h: [u32; 8] = [
        0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
        0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
    ];

    // Round constants (first 32 bits of the fractional parts of the cube
    // roots of the first 64 primes).
    #[rustfmt::skip]
    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,
    ];

    // Pre-processing: pad message to 512-bit blocks.
    let bit_len = (data.len() as u64).wrapping_mul(8);
    let mut msg = data.to_vec();
    msg.push(0x80);
    while (msg.len() % 64) != 56 {
        msg.push(0x00);
    }
    msg.extend_from_slice(&bit_len.to_be_bytes());

    for block in msg.chunks(64) {
        let mut w = [0u32; 64];
        for (i, chunk) in block.chunks(4).enumerate().take(16) {
            w[i] = u32::from_be_bytes([chunk[0], chunk[1], chunk[2], chunk[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(|v| format!("{:08x}", v))
        .collect::<String>()
}