test: proptest property testing + cargo-fuzz fuzzing for donglora-cobs

crates/donglora-cobs/fuzz/Cargo.toml

@@ -0,0 +1,24 @@
+[package]
+name = "donglora-cobs-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+donglora-cobs = { path = ".." }
+
+[[bin]]
+name = "fuzz_decode"
+path = "fuzz_targets/fuzz_decode.rs"
+test = false
+doc = false
+
+[[bin]]
+name = "fuzz_roundtrip"
+path = "fuzz_targets/fuzz_roundtrip.rs"
+test = false
+doc = false

crates/donglora-cobs/fuzz/fuzz_targets/fuzz_decode.rs

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+//! Fuzz target: feed arbitrary bytes to decode(). Must never panic.
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    let mut buf = [0u8; 2048];
+    // Must not panic — may return None on invalid input.
+    let _ = donglora_cobs::decode(data, &mut buf);
+});

crates/donglora-cobs/fuzz/fuzz_targets/fuzz_roundtrip.rs

@@ -0,0 +1,30 @@
+//! Fuzz target: encode then decode arbitrary input. Output must match input.
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    if data.len() > 1024 {
+        return; // skip huge inputs to keep fuzzing fast
+    }
+
+    let max_enc = donglora_cobs::max_encoded_len(data.len()) + 1;
+    let mut enc_buf = vec![0u8; max_enc];
+
+    let enc_len = match donglora_cobs::encode(data, &mut enc_buf) {
+        Some(n) => n,
+        None => return, // encode failed (buffer too small shouldn't happen, but skip)
+    };
+    let encoded = &enc_buf[..enc_len];
+
+    // Encoded output must never contain 0x00.
+    assert!(!encoded.contains(&0x00), "encoded contains sentinel");
+
+    let mut dec_buf = vec![0u8; data.len() + 1];
+    let dec_len = donglora_cobs::decode(encoded, &mut dec_buf)
+        .expect("decode failed after successful encode");
+
+    assert_eq!(
+        &dec_buf[..dec_len], data,
+        "round-trip mismatch: encode→decode produced different output"
+    );
+});