Wire fuzz harness into verify workflow

.gitignore

@@ -1,3 +1,7 @@
 .DS_Store
 Cargo.lock
 target/
+fuzz/artifacts/
+fuzz/corpus/
+fuzz/coverage/
+fuzz/target/

CHANGELOG.md

@@ -1,6 +1,9 @@
 # Changelog
 
 ## Unreleased
+- added proptest coverage for prefix/suffix invariants and introduced a fuzz target for mutating `Bytes` operations
+- extended `verify.sh` to install cargo-fuzz and execute deterministic fuzz runs alongside Kani proofs
+- added Kani proofs ensuring `is_subslice` accepts only slices from the original allocation
 - add Kani proof checking `Bytes::downcast_to_owner` for matching and mismatched owners
 - added Kani verification harnesses for `Bytes::pop_front` and `Bytes::pop_back`
 - avoid flushing empty memory maps in `Section::freeze` to prevent macOS errors

INVENTORY.md

@@ -6,6 +6,7 @@
 ## Desired Functionality
 - Add Kani proofs for winnow view helpers.
 - Add test covering freezing an empty section to guard against flush errors on macOS.
+- Explore how to model `ByteArea` for Kani or fuzzing without depending on OS-backed memory maps.
 
 ## Discovered Issues
 - None at the moment.

README.md

@@ -175,10 +175,17 @@ Run `./scripts/preflight.sh` from the repository root before committing. The
 script formats the code and executes all tests using Python 3.12 for the `pyo3`
 feature.
 
-Kani proofs are executed separately with `./scripts/verify.sh`, which should be
-run on a dedicated system. The script will install the Kani verifier
-automatically. Verification can take a long time and isn't needed for quick
-development iterations.
+Kani proofs and deterministic fuzz smoke tests are executed with
+`./scripts/verify.sh`, which should be run on a dedicated system. The script
+installs the Kani verifier, `cargo-fuzz`, and the nightly toolchain before
+running `cargo kani --workspace --all-features` followed by a bounded
+`cargo +nightly fuzz run`. Override the fuzz target or arguments by setting
+`FUZZ_TARGET` or `FUZZ_ARGS` in the environment. Verification can take a long
+time and isn't needed for quick development iterations.
+
+For exploratory fuzzing use `cargo fuzz run bytes_mut_ops`. The fuzz target
+mirrors a simple vector model to ensure helpers like `take_prefix` and
+`pop_front` remain consistent when exercised by randomized sequences.
 
 ## Glossary
 

fuzz/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "anybytes-fuzz"
+version = "0.0.0"
+edition = "2021"
+publish = false
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+anybytes = { path = ".." }
+
+[dev-dependencies]
+arbitrary = { version = "1", features = ["derive"] }
+
+[[bin]]
+name = "bytes_mut_ops"
+path = "fuzz_targets/bytes_mut_ops.rs"
+test = false
+doc = false

fuzz/fuzz_targets/bytes_mut_ops.rs

@@ -0,0 +1,103 @@
+#![no_main]
+
+use anybytes::Bytes;
+use arbitrary::{Arbitrary, Result as ArbResult, Unstructured};
+use libfuzzer_sys::fuzz_target;
+
+#[derive(Debug)]
+enum Operation {
+    TakePrefix(u16),
+    TakeSuffix(u16),
+    PopFront,
+    PopBack,
+}
+
+impl<'a> Arbitrary<'a> for Operation {
+    fn arbitrary(u: &mut Unstructured<'a>) -> ArbResult<Self> {
+        let tag = u.int_in_range::<u8>(0..=3)?;
+        let op = match tag {
+            0 => Operation::TakePrefix(u.arbitrary()?),
+            1 => Operation::TakeSuffix(u.arbitrary()?),
+            2 => Operation::PopFront,
+            _ => Operation::PopBack,
+        };
+        Ok(op)
+    }
+}
+
+#[derive(Debug)]
+struct FuzzCase {
+    data: Vec<u8>,
+    ops: Vec<Operation>,
+}
+
+impl<'a> Arbitrary<'a> for FuzzCase {
+    fn arbitrary(u: &mut Unstructured<'a>) -> ArbResult<Self> {
+        let len = u.int_in_range::<usize>(0..=64)?;
+        let mut data = Vec::with_capacity(len);
+        for _ in 0..len {
+            data.push(u.arbitrary()?);
+        }
+
+        let ops_len = u.int_in_range::<usize>(0..=64)?;
+        let mut ops = Vec::with_capacity(ops_len);
+        for _ in 0..ops_len {
+            ops.push(u.arbitrary()?);
+        }
+
+        Ok(Self { data, ops })
+    }
+}
+
+fuzz_target!(|case: FuzzCase| {
+    let mut bytes = Bytes::from(case.data.clone());
+    let mut model = case.data;
+
+    for op in case.ops {
+        match op {
+            Operation::TakePrefix(n) => {
+                let len = n as usize;
+                let result = bytes.take_prefix(len);
+                if len <= model.len() {
+                    let expected: Vec<u8> = model.drain(..len).collect();
+                    let prefix = result.expect("prefix should exist");
+                    assert_eq!(prefix.as_ref(), expected.as_slice());
+                    assert_eq!(bytes.as_ref(), model.as_slice());
+                } else {
+                    assert!(result.is_none());
+                    assert_eq!(bytes.as_ref(), model.as_slice());
+                }
+            }
+            Operation::TakeSuffix(n) => {
+                let len = n as usize;
+                let result = bytes.take_suffix(len);
+                if len <= model.len() {
+                    let split = model.len() - len;
+                    let expected = model.split_off(split);
+                    let suffix = result.expect("suffix should exist");
+                    assert_eq!(suffix.as_ref(), expected.as_slice());
+                    assert_eq!(bytes.as_ref(), model.as_slice());
+                } else {
+                    assert!(result.is_none());
+                    assert_eq!(bytes.as_ref(), model.as_slice());
+                }
+            }
+            Operation::PopFront => {
+                let expected = if model.is_empty() {
+                    None
+                } else {
+                    Some(model.remove(0))
+                };
+                let got = bytes.pop_front();
+                assert_eq!(got, expected);
+                assert_eq!(bytes.as_ref(), model.as_slice());
+            }
+            Operation::PopBack => {
+                let expected = model.pop();
+                let got = bytes.pop_back();
+                assert_eq!(got, expected);
+                assert_eq!(bytes.as_ref(), model.as_slice());
+            }
+        }
+    }
+});

scripts/verify.sh

@@ -11,6 +11,26 @@ cargo install rustfmt || true
 # Install the Kani verifier as needed; this is also idempotent.
 cargo install --locked kani-verifier || true
 
+# Install cargo-fuzz to run libFuzzer targets. This subcommand is optional
+# during development so we ignore installation failures here as well.
+cargo install cargo-fuzz || true
+
+# Ensure the nightly toolchain is present for cargo-fuzz and required LLVM tools
+rustup toolchain install nightly || true
+rustup component add llvm-tools-preview --toolchain nightly || true
+
 # Run all Kani proofs in the workspace
 cargo kani --workspace --all-features
 
+# Execute fuzz targets with deterministic settings so verification stays
+# reproducible. The default run count can be overridden by setting FUZZ_ARGS.
+FUZZ_TARGET="${FUZZ_TARGET:-bytes_mut_ops}"
+FUZZ_ARG_STRING="${FUZZ_ARGS:-}"
+if [[ -n "$FUZZ_ARG_STRING" ]]; then
+  IFS=' ' read -r -a FUZZ_ARG_ARRAY <<< "$FUZZ_ARG_STRING"
+else
+  FUZZ_ARG_ARRAY=(-seed=1 -runs=50000)
+fi
+
+cargo +nightly fuzz run "$FUZZ_TARGET" -- "${FUZZ_ARG_ARRAY[@]}"
+

src/bytes.rs

@@ -718,4 +718,43 @@ mod verification {
         };
         assert_eq!(returned.as_ref(), data.as_slice());
     }
+
+    #[kani::proof]
+    #[kani::unwind(16)]
+    pub fn check_is_subslice_accepts_ranges() {
+        let data: Vec<u8> = Vec::bounded_any::<16>();
+        let bytes = Bytes::from_source(data.clone());
+
+        let start: usize = kani::any();
+        let end: usize = kani::any();
+        kani::assume(start <= end);
+        kani::assume(end <= data.len());
+
+        let slice = &bytes.as_ref()[start..end];
+        assert!(is_subslice(bytes.as_ref(), slice));
+    }
+
+    #[kani::proof]
+    #[kani::unwind(16)]
+    pub fn check_is_subslice_rejects_disjoint_ranges() {
+        let data: Vec<u8> = Vec::bounded_any::<16>();
+        let other: Vec<u8> = Vec::bounded_any::<8>();
+
+        let base_len = data.len();
+        kani::assume(base_len > 0);
+        let base_ptr = data.as_ptr();
+
+        let other_len = other.len();
+        kani::assume(other_len > 0);
+        let other_ptr = other.as_ptr();
+
+        let base_start = base_ptr as usize;
+        let base_end = base_start + base_len;
+        let other_start = other_ptr as usize;
+        let other_end = other_start + other_len;
+        kani::assume(other_end <= base_start || other_start >= base_end);
+
+        let bytes = Bytes::from_source(data);
+        assert!(!is_subslice(bytes.as_ref(), other.as_slice()));
+    }
 }

src/tests.rs

@@ -26,6 +26,35 @@ proptest! {
         prop_assert_eq!(&b[..], &a[..b.len()]);
         prop_assert!(b.is_empty() || a.as_ptr() == b.as_ptr());
     }
+
+    #[test]
+    fn test_take_prefix_matches_split(data in proptest::collection::vec(any::<u8>(), 0..64)) {
+        for len in 0..=data.len() {
+            let mut bytes = Bytes::from(data.clone());
+            let prefix = bytes.take_prefix(len).expect("prefix within bounds");
+            prop_assert_eq!(prefix.as_ref(), &data[..len]);
+            prop_assert_eq!(bytes.as_ref(), &data[len..]);
+        }
+
+        let mut bytes = Bytes::from(data.clone());
+        prop_assert!(bytes.take_prefix(data.len() + 1).is_none());
+        prop_assert_eq!(bytes.as_ref(), data.as_slice());
+    }
+
+    #[test]
+    fn test_take_suffix_matches_split(data in proptest::collection::vec(any::<u8>(), 0..64)) {
+        for len in 0..=data.len() {
+            let mut bytes = Bytes::from(data.clone());
+            let suffix = bytes.take_suffix(len).expect("suffix within bounds");
+            let split = data.len() - len;
+            prop_assert_eq!(suffix.as_ref(), &data[split..]);
+            prop_assert_eq!(bytes.as_ref(), &data[..split]);
+        }
+
+        let mut bytes = Bytes::from(data.clone());
+        prop_assert!(bytes.take_suffix(data.len() + 1).is_none());
+        prop_assert_eq!(bytes.as_ref(), data.as_slice());
+    }
 }
 
 #[test]