zerocopy 0.8.56: zerocopy::FromBytes

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Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify zerocopy::FromBytes in pkg:cargo/zerocopy@0.8.56
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:cargo/zerocopy@0.8.56
Demonstrate these symbols/APIs:
  - zerocopy::FromBytes

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:70232df14e3e07ac4f6776436c71760601778605718fc92e0005abfac176ef3a","contract":["FromBytes reads scalar values from a byte slice with read_from_bytes","FromBytes fails with error when byte slice length is insufficient","FromBytes reads prefix from byte slice returning parsed value and remaining suffix","FromBytes reads suffix from byte slice returning remaining prefix and parsed value","FromBytes casts aligned byte buffer into typed scalar reference with ref_from_bytes","FromBytes casts aligned byte buffer into typed slice reference with ref_from_bytes","FromBytes mutates memory in-place through mutable reference with mut_from_bytes"],"goal":"verify zerocopy::FromBytes in pkg:cargo/zerocopy@0.8.56","kind":"HOW","packages":["pkg:cargo/zerocopy@0.8.56"],"schemaVersion":1,"symbols":["zerocopy::FromBytes"]},"contractCommand":["cargo","run","--offline"],"environment":{"arch":"x64","distro":"alpine","ecosystem":"cargo","libc":"musl","os":"linux","packageManager":"cargo","schemaVersion":1},"license":"MIT-0","packages":["pkg:cargo/zerocopy@0.8.56"],"schemaVersion":1,"subject":"pkg:cargo/zerocopy@0.8.56","symbols":["zerocopy::FromBytes"],"verifierAdapter":"cargo@1"}

{
  "schemaVersion": 1,
  "goal": "verify zerocopy::FromBytes in pkg:cargo/zerocopy@0.8.56",
  "kind": "HOW",
  "packages": [
    "pkg:cargo/zerocopy@0.8.56"
  ],
  "symbols": [
    "zerocopy::FromBytes"
  ]
}

//! Clean-room verification sample for zerocopy.

pub use zerocopy::*;

use zerocopy::FromBytes;

#[repr(align(4))]
struct Aligned4<T>(T);

#[repr(align(8))]
struct Aligned8<T>(T);

fn main() {
    // 1. FromBytes reads scalar values from a byte slice with read_from_bytes
    let bytes: [u8; 4] = [0x78, 0x56, 0x34, 0x12];
    let val = u32::read_from_bytes(&bytes).expect("read_from_bytes should succeed");
    assert_eq!(val.to_ne_bytes(), [0x78, 0x56, 0x34, 0x12]);

    // 2. FromBytes fails with error when byte slice length is insufficient
    let short_bytes = [0x12, 0x34];
    assert!(u32::read_from_bytes(&short_bytes).is_err());

    // 3. FromBytes reads prefix from byte slice returning parsed value and remaining suffix
    let stream = [0x01, 0x02, 0x03, 0x04, 0xAA, 0xBB];
    let (prefix, rest) = u32::read_from_prefix(&stream).expect("read_from_prefix should succeed");
    assert_eq!(prefix.to_ne_bytes(), [0x01, 0x02, 0x03, 0x04]);
    assert_eq!(rest, &[0xAA, 0xBB]);

    // 4. FromBytes reads suffix from byte slice returning remaining prefix and parsed value
    let stream2 = [0xAA, 0xBB, 0x01, 0x02, 0x03, 0x04];
    let (rest2, suffix) = u32::read_from_suffix(&stream2).expect("read_from_suffix should succeed");
    assert_eq!(rest2, &[0xAA, 0xBB]);
    assert_eq!(suffix.to_ne_bytes(), [0x01, 0x02, 0x03, 0x04]);

    // 5. FromBytes casts aligned byte buffer into typed scalar reference with ref_from_bytes
    let aligned_scalar = Aligned4([0x10u8, 0x20, 0x30, 0x40]);
    let scalar_ref = u32::ref_from_bytes(&aligned_scalar.0).expect("aligned ref_from_bytes should succeed");
    assert_eq!(scalar_ref.to_ne_bytes(), [0x10, 0x20, 0x30, 0x40]);

    // 6. FromBytes casts aligned byte buffer into typed slice reference with ref_from_bytes
    let aligned_slice = Aligned8([0x01u8, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08]);
    let slice_ref = <[u16]>::ref_from_bytes(&aligned_slice.0).expect("aligned slice ref_from_bytes should succeed");
    assert_eq!(slice_ref.len(), 4);
    assert_eq!(slice_ref[0].to_ne_bytes(), [0x01, 0x02]);
    assert_eq!(slice_ref[3].to_ne_bytes(), [0x07, 0x08]);

    // 7. FromBytes mutates memory in-place through mutable reference with mut_from_bytes
    let mut mut_buf = Aligned4([0x00u8; 4]);
    let mut_ref = u32::mut_from_bytes(&mut mut_buf.0).expect("mut_from_bytes should succeed");
    *mut_ref = u32::from_ne_bytes([0x11, 0x22, 0x33, 0x44]);
    assert_eq!(mut_buf.0, [0x11, 0x22, 0x33, 0x44]);

    println!("All zerocopy::FromBytes contract assertions passed successfully.");
}