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

.gitignore

@@ -5,3 +5,5 @@ src/board/mod.rs
 __pycache__/
 .hypothesis/
 examples/meshcore/corpus/generated/
+crates/donglora-cobs/fuzz/corpus/
+crates/donglora-cobs/fuzz/artifacts/

Cargo.lock

@@ -56,6 +56,21 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "bit-set"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "08807e080ed7f9d5433fa9b275196cfc35414f66a0c79d864dc51a0d825231a3"
+dependencies = [
+ "bit-vec",
+]
+
+[[package]]
+name = "bit-vec"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e764a1d40d510daf35e07be9eb06e75770908c27d411ee6c92109c9840eaaf7"
+
 [[package]]
 name = "bitfield"
 version = "0.13.2"
@@ -367,7 +382,8 @@ name = "donglora-cobs"
 version = "0.1.0"
 dependencies = [
  "corncobs",
- "rand",
+ "proptest",
+ "rand 0.8.5",
 ]
 
 [[package]]
@@ -485,7 +501,7 @@ dependencies = [
  "nrf5340-net-pac",
  "nrf9120-pac",
  "nrf9160-pac",
- "rand_core",
+ "rand_core 0.6.4",
 ]
 
 [[package]]
@@ -742,6 +758,16 @@ version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
 
+[[package]]
+name = "errno"
+version = "0.3.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "39cab71617ae0d63f51a36d69f866391735b51691dbda63cf6f96d042b63efeb"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
 [[package]]
 name = "esp-backtrace"
 version = "0.14.2"
@@ -813,7 +839,7 @@ dependencies = [
  "nb 1.1.0",
  "paste",
  "portable-atomic",
- "rand_core",
+ "rand_core 0.6.4",
  "serde",
  "strum",
  "ufmt-write",
@@ -918,6 +944,12 @@ dependencies = [
  "vcell",
 ]
 
+[[package]]
+name = "fastrand"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37909eebbb50d72f9059c3b6d82c0463f2ff062c9e95845c43a6c9c0355411be"
+
 [[package]]
 name = "fixed"
 version = "1.29.0"
@@ -945,6 +977,12 @@ version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
 
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
 [[package]]
 name = "fugit"
 version = "0.3.9"
@@ -1000,6 +1038,31 @@ dependencies = [
  "wasi",
 ]
 
+[[package]]
+name = "getrandom"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "899def5c37c4fd7b2664648c28120ecec138e4d395b459e5ca34f9cce2dd77fd"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi 5.3.0",
+ "wasip2",
+]
+
+[[package]]
+name = "getrandom"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0de51e6874e94e7bf76d726fc5d13ba782deca734ff60d5bb2fb2607c7406555"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi 6.0.0",
+ "wasip2",
+ "wasip3",
+]
+
 [[package]]
 name = "half"
 version = "2.7.1"
@@ -1029,6 +1092,15 @@ dependencies = [
  "ahash",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.15.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9229cfe53dfd69f0609a49f65461bd93001ea1ef889cd5529dd176593f5338a1"
+dependencies = [
+ "foldhash",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.16.1"
@@ -1051,6 +1123,12 @@ version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2304e00983f87ffb38b55b444b5e3b60a884b5d30c0fca7d82fe33449bbe55ea"
 
+[[package]]
+name = "id-arena"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3d3067d79b975e8844ca9eb072e16b31c3c1c36928edf9c6789548c524d0d954"
+
 [[package]]
 name = "ident_case"
 version = "1.0.1"
@@ -1065,14 +1143,34 @@ checksum = "7714e70437a7dc3ac8eb7e6f8df75fd8eb422675fc7678aff7364301092b1017"
 dependencies = [
  "equivalent",
  "hashbrown 0.16.1",
+ "serde",
+ "serde_core",
 ]
 
+[[package]]
+name = "itoa"
+version = "1.0.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8f42a60cbdf9a97f5d2305f08a87dc4e09308d1276d28c869c684d7777685682"
+
+[[package]]
+name = "leb128fmt"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09edd9e8b54e49e587e4f6295a7d29c3ea94d469cb40ab8ca70b288248a81db2"
+
 [[package]]
 name = "libc"
 version = "0.2.183"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b5b646652bf6661599e1da8901b3b9522896f01e736bad5f723fe7a3a27f899d"
 
+[[package]]
+name = "linux-raw-sys"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a66949e030da00e8c7d4434b251670a91556f4144941d37452769c25d58a53"
+
 [[package]]
 name = "litrs"
 version = "0.4.2"
@@ -1383,6 +1481,16 @@ dependencies = [
  "zerocopy",
 ]
 
+[[package]]
+name = "prettyplease"
+version = "0.2.37"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "479ca8adacdd7ce8f1fb39ce9ecccbfe93a3f1344b3d0d97f20bc0196208f62b"
+dependencies = [
+ "proc-macro2",
+ "syn 2.0.117",
+]
+
 [[package]]
 name = "proc-macro-crate"
 version = "3.2.0"
@@ -1447,6 +1555,25 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "proptest"
+version = "1.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4b45fcc2344c680f5025fe57779faef368840d0bd1f42f216291f0dc4ace4744"
+dependencies = [
+ "bit-set",
+ "bit-vec",
+ "bitflags 2.11.0",
+ "num-traits",
+ "rand 0.9.2",
+ "rand_chacha 0.9.0",
+ "rand_xorshift",
+ "regex-syntax",
+ "rusty-fork",
+ "tempfile",
+ "unarray",
+]
+
 [[package]]
 name = "pulldown-cmark"
 version = "0.11.3"
@@ -1458,6 +1585,12 @@ dependencies = [
  "unicase",
 ]
 
+[[package]]
+name = "quick-error"
+version = "1.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1d01941d82fa2ab50be1e79e6714289dd7cde78eba4c074bc5a4374f650dfe0"
+
 [[package]]
 name = "quote"
 version = "1.0.45"
@@ -1467,6 +1600,18 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "r-efi"
+version = "5.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "69cdb34c158ceb288df11e18b4bd39de994f6657d83847bdffdbd7f346754b0f"
+
+[[package]]
+name = "r-efi"
+version = "6.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
+
 [[package]]
 name = "r0"
 version = "1.0.0"
@@ -1486,8 +1631,18 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
 dependencies = [
  "libc",
- "rand_chacha",
+ "rand_chacha 0.3.1",
- "rand_core",
+ "rand_core 0.6.4",
+]
+
+[[package]]
+name = "rand"
+version = "0.9.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6db2770f06117d490610c7488547d543617b21bfa07796d7a12f6f1bd53850d1"
+dependencies = [
+ "rand_chacha 0.9.0",
+ "rand_core 0.9.5",
 ]
 
 [[package]]
@@ -1497,7 +1652,17 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e6c10a63a0fa32252be49d21e7709d4d4baf8d231c2dbce1eaa8141b9b127d88"
 dependencies = [
  "ppv-lite86",
- "rand_core",
+ "rand_core 0.6.4",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d3022b5f1df60f26e1ffddd6c66e8aa15de382ae63b3a0c1bfc0e4d3e3f325cb"
+dependencies = [
+ "ppv-lite86",
+ "rand_core 0.9.5",
 ]
 
 [[package]]
@@ -1506,9 +1671,33 @@ version = "0.6.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
 dependencies = [
- "getrandom",
+ "getrandom 0.2.17",
 ]
 
+[[package]]
+name = "rand_core"
+version = "0.9.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "76afc826de14238e6e8c374ddcc1fa19e374fd8dd986b0d2af0d02377261d83c"
+dependencies = [
+ "getrandom 0.3.4",
+]
+
+[[package]]
+name = "rand_xorshift"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "513962919efc330f829edb2535844d1b912b0fbe2ca165d613e4e8788bb05a5a"
+dependencies = [
+ "rand_core 0.9.5",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc897dd8d9e8bd1ed8cdad82b5966c3e0ecae09fb1907d58efaa013543185d0a"
+
 [[package]]
 name = "riscv"
 version = "0.12.1"
@@ -1556,7 +1745,20 @@ version = "0.2.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "138e3e0acb6c9fb258b19b67cb8abd63c00679d2851805ea151465464fe9030a"
 dependencies = [
- "semver",
+ "semver 0.9.0",
+]
+
+[[package]]
+name = "rustix"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6fe4565b9518b83ef4f91bb47ce29620ca828bd32cb7e408f0062e9930ba190"
+dependencies = [
+ "bitflags 2.11.0",
+ "errno",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys",
 ]
 
 [[package]]
@@ -1565,6 +1767,18 @@ version = "1.0.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
 
+[[package]]
+name = "rusty-fork"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cc6bf79ff24e648f6da1f8d1f011e9cac26491b619e6b9280f2b47f1774e6ee2"
+dependencies = [
+ "fnv",
+ "quick-error",
+ "tempfile",
+ "wait-timeout",
+]
+
 [[package]]
 name = "scopeguard"
 version = "1.2.0"
@@ -1586,6 +1800,12 @@ dependencies = [
  "semver-parser",
 ]
 
+[[package]]
+name = "semver"
+version = "1.0.27"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d767eb0aabc880b29956c35734170f26ed551a859dbd361d140cdbeca61ab1e2"
+
 [[package]]
 name = "semver-parser"
 version = "0.7.0"
@@ -1622,6 +1842,19 @@ dependencies = [
  "syn 2.0.117",
 ]
 
+[[package]]
+name = "serde_json"
+version = "1.0.149"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "83fc039473c5595ace860d8c4fafa220ff474b3fc6bfdb4293327f1a37e94d86"
+dependencies = [
+ "itoa",
+ "memchr",
+ "serde",
+ "serde_core",
+ "zmij",
+]
+
 [[package]]
 name = "serde_spanned"
 version = "0.6.9"
@@ -1730,6 +1963,19 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "tempfile"
+version = "3.27.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32497e9a4c7b38532efcdebeef879707aa9f794296a4f0244f6f69e9bc8574bd"
+dependencies = [
+ "fastrand",
+ "getrandom 0.4.2",
+ "once_cell",
+ "rustix",
+ "windows-sys",
+]
+
 [[package]]
 name = "termcolor"
 version = "1.4.1"
@@ -1812,6 +2058,12 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e87a2ed6b42ec5e28cc3b94c09982969e9227600b2e3dcbc1db927a84c06bd69"
 
+[[package]]
+name = "unarray"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eaea85b334db583fe3274d12b4cd1880032beab409c0d774be044d4480ab9a94"
+
 [[package]]
 name = "unicase"
 version = "2.9.0"
@@ -1824,6 +2076,12 @@ version = "1.0.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e6e4313cd5fcd3dad5cafa179702e2b244f760991f45397d14d4ebf38247da75"
 
+[[package]]
+name = "unicode-xid"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ebc1c04c71510c7f702b52b7c350734c9ff1295c464a03335b00bb84fc54f853"
+
 [[package]]
 name = "usb-device"
 version = "0.3.2"
@@ -1898,12 +2156,73 @@ dependencies = [
  "vcell",
 ]
 
+[[package]]
+name = "wait-timeout"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09ac3b126d3914f9849036f826e054cbabdc8519970b8998ddaf3b5bd3c65f11"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "wasi"
 version = "0.11.1+wasi-snapshot-preview1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ccf3ec651a847eb01de73ccad15eb7d99f80485de043efb2f370cd654f4ea44b"
 
+[[package]]
+name = "wasip2"
+version = "1.0.2+wasi-0.2.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9517f9239f02c069db75e65f174b3da828fe5f5b945c4dd26bd25d89c03ebcf5"
+dependencies = [
+ "wit-bindgen",
+]
+
+[[package]]
+name = "wasip3"
+version = "0.4.0+wasi-0.3.0-rc-2026-01-06"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5428f8bf88ea5ddc08faddef2ac4a67e390b88186c703ce6dbd955e1c145aca5"
+dependencies = [
+ "wit-bindgen",
+]
+
+[[package]]
+name = "wasm-encoder"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "990065f2fe63003fe337b932cfb5e3b80e0b4d0f5ff650e6985b1048f62c8319"
+dependencies = [
+ "leb128fmt",
+ "wasmparser",
+]
+
+[[package]]
+name = "wasm-metadata"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb0e353e6a2fbdc176932bbaab493762eb1255a7900fe0fea1a2f96c296cc909"
+dependencies = [
+ "anyhow",
+ "indexmap",
+ "wasm-encoder",
+ "wasmparser",
+]
+
+[[package]]
+name = "wasmparser"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47b807c72e1bac69382b3a6fb3dbe8ea4c0ed87ff5629b8685ae6b9a611028fe"
+dependencies = [
+ "bitflags 2.11.0",
+ "hashbrown 0.15.5",
+ "indexmap",
+ "semver 1.0.27",
+]
+
 [[package]]
 name = "winapi-util"
 version = "0.1.11"
@@ -1937,6 +2256,94 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "wit-bindgen"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d7249219f66ced02969388cf2bb044a09756a083d0fab1e566056b04d9fbcaa5"
+dependencies = [
+ "wit-bindgen-rust-macro",
+]
+
+[[package]]
+name = "wit-bindgen-core"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ea61de684c3ea68cb082b7a88508a8b27fcc8b797d738bfc99a82facf1d752dc"
+dependencies = [
+ "anyhow",
+ "heck",
+ "wit-parser",
+]
+
+[[package]]
+name = "wit-bindgen-rust"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b7c566e0f4b284dd6561c786d9cb0142da491f46a9fbed79ea69cdad5db17f21"
+dependencies = [
+ "anyhow",
+ "heck",
+ "indexmap",
+ "prettyplease",
+ "syn 2.0.117",
+ "wasm-metadata",
+ "wit-bindgen-core",
+ "wit-component",
+]
+
+[[package]]
+name = "wit-bindgen-rust-macro"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0c0f9bfd77e6a48eccf51359e3ae77140a7f50b1e2ebfe62422d8afdaffab17a"
+dependencies = [
+ "anyhow",
+ "prettyplease",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.117",
+ "wit-bindgen-core",
+ "wit-bindgen-rust",
+]
+
+[[package]]
+name = "wit-component"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d66ea20e9553b30172b5e831994e35fbde2d165325bec84fc43dbf6f4eb9cb2"
+dependencies = [
+ "anyhow",
+ "bitflags 2.11.0",
+ "indexmap",
+ "log",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "wasm-encoder",
+ "wasm-metadata",
+ "wasmparser",
+ "wit-parser",
+]
+
+[[package]]
+name = "wit-parser"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ecc8ac4bc1dc3381b7f59c34f00b67e18f910c2c0f50015669dde7def656a736"
+dependencies = [
+ "anyhow",
+ "id-arena",
+ "indexmap",
+ "log",
+ "semver 1.0.27",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "unicode-xid",
+ "wasmparser",
+]
+
 [[package]]
 name = "xtensa-lx"
 version = "0.9.0"
@@ -1998,3 +2405,9 @@ dependencies = [
  "quote",
  "syn 2.0.117",
 ]
+
+[[package]]
+name = "zmij"
+version = "1.0.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b8848ee67ecc8aedbaf3e4122217aff892639231befc6a1b58d29fff4c2cabaa"

crates/donglora-cobs/Cargo.toml

@@ -10,4 +10,5 @@ default = []
 
 [dev-dependencies]
 corncobs = "0.1"
+proptest = "1"
 rand = "0.8"

crates/donglora-cobs/README.md

@@ -21,11 +21,21 @@ benchmark-optimized for streaming applications.
 ## Testing
 
 ```sh
+# Unit tests + property tests + interop
 cargo test -p donglora-cobs
+
+# Fuzz testing (requires cargo-fuzz: cargo install cargo-fuzz)
+cd crates/donglora-cobs
+cargo +nightly fuzz run fuzz_decode -- -max_total_time=60
+cargo +nightly fuzz run fuzz_roundtrip -- -max_total_time=60
 ```
 
 Tests include:
 - 18 canonical COBS vectors (Wikipedia / IEEE/ACM spec)
 - Round-trip verification for various payload sizes
-- 8 interop tests cross-validating against `corncobs` (dev-dependency)
+- 8 interop tests cross-validating against `corncobs`
 - 500 randomized round-trip payloads verified against `corncobs`
+- **5 proptest properties** (~1280 random inputs): round-trip, interop
+  encode/decode both directions, length bounds, decode-never-panics
+- **2 fuzz targets**: `fuzz_decode` (arbitrary bytes → must not panic)
+  and `fuzz_roundtrip` (encode→decode must match)

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

@@ -0,0 +1,9 @@
+//! 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"
+    );
+});

crates/donglora-cobs/src/lib.rs

@@ -486,3 +486,72 @@ mod tests {
         }
     }
 }
+
+// ── Property-based tests (proptest) ─────────────────────────────
+
+#[cfg(test)]
+mod proptests {
+    extern crate alloc;
+    use alloc::vec;
+    use alloc::vec::Vec;
+    use super::*;
+    use proptest::prelude::*;
+
+    // Round-trip: encode then decode must recover the original.
+    proptest! {
+        #[test]
+        fn roundtrip_any(data in proptest::collection::vec(any::<u8>(), 0..1024)) {
+            let mut enc_buf = vec![0u8; max_encoded_len(data.len()) + 1];
+            let enc_len = encode(&data, &mut enc_buf).unwrap();
+            let encoded = &enc_buf[..enc_len];
+
+            // Encoded output must never contain 0x00.
+            prop_assert!(!encoded.contains(&0x00));
+
+            let mut dec_buf = vec![0u8; data.len() + 1];
+            let dec_len = decode(encoded, &mut dec_buf).unwrap();
+            prop_assert_eq!(&dec_buf[..dec_len], &data[..]);
+        }
+
+        // Our encode → corncobs decode must match.
+        #[test]
+        fn interop_our_encode_their_decode(data in proptest::collection::vec(any::<u8>(), 0..1024)) {
+            let mut enc_buf = vec![0u8; max_encoded_len(data.len()) + 2];
+            let enc_len = encode(&data, &mut enc_buf).unwrap();
+            // Append sentinel for corncobs.
+            enc_buf[enc_len] = 0x00;
+
+            let mut dec_buf = vec![0u8; data.len() + 1];
+            let dec_len = corncobs::decode_buf(&enc_buf[..enc_len + 1], &mut dec_buf).unwrap();
+            prop_assert_eq!(&dec_buf[..dec_len], &data[..]);
+        }
+
+        // corncobs encode → our decode must match.
+        #[test]
+        fn interop_their_encode_our_decode(data in proptest::collection::vec(any::<u8>(), 0..1024)) {
+            let mut enc_buf = vec![0u8; corncobs::max_encoded_len(data.len())];
+            let enc_len = corncobs::encode_buf(&data, &mut enc_buf);
+            // Strip trailing sentinel for our decoder.
+            let data_end = enc_buf[..enc_len].iter().rposition(|&b| b != 0x00).map_or(0, |i| i + 1);
+
+            let mut dec_buf = vec![0u8; data.len() + 1];
+            let dec_len = decode(&enc_buf[..data_end], &mut dec_buf).unwrap();
+            prop_assert_eq!(&dec_buf[..dec_len], &data[..]);
+        }
+
+        // Encoded length is always within the theoretical maximum.
+        #[test]
+        fn encoded_length_bounded(data in proptest::collection::vec(any::<u8>(), 0..1024)) {
+            let mut enc_buf = vec![0u8; max_encoded_len(data.len()) + 1];
+            let enc_len = encode(&data, &mut enc_buf).unwrap();
+            prop_assert!(enc_len <= max_encoded_len(data.len()));
+        }
+
+        // Decoding random garbage must never panic (returns None on invalid input).
+        #[test]
+        fn decode_never_panics(data in proptest::collection::vec(any::<u8>(), 0..512)) {
+            let mut dec_buf = vec![0u8; data.len() + 256];
+            let _ = decode(&data, &mut dec_buf); // may return None, must not panic
+        }
+    }
+}