test: switch from roundtrip based tests to e2e based fuzzers (#59)

This is stacked on top of #58

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: 3 people

.github/workflows/ci.yml

@@ -67,8 +67,9 @@ jobs:
     strategy:
       matrix:
         include:
-          - fuzz_target: fastpfor_cpp
-          - fuzz_target: fastpfor_rust
+          - fuzz_target: cpp_roundtrip
+          - fuzz_target: rust_compress_oracle
+          - fuzz_target: rust_decompress_oracle
 
     steps:
       - uses: actions/checkout@v6

fuzz/Cargo.toml

@@ -17,13 +17,19 @@ fastpfor = { path = "..", features = ["cpp", "rust"] }
 members = ["."]
 
 [[bin]]
-name = "fastpfor_rust"
-path = "fuzz_targets/fastpfor_rust.rs"
+name = "cpp_roundtrip"
+path = "fuzz_targets/cpp_roundtrip.rs"
 test = false
 doc = false
 
 [[bin]]
-name = "fastpfor_cpp"
-path = "fuzz_targets/fastpfor_cpp.rs"
+name = "rust_compress_oracle"
+path = "fuzz_targets/rust_compress_oracle.rs"
+test = false
+doc = false
+
+[[bin]]
+name = "rust_decompress_oracle"
+path = "fuzz_targets/rust_decompress_oracle.rs"
 test = false
 doc = false

fuzz/README.md

@@ -1,36 +1,17 @@
 # Fuzzing FastPFOR
 
-This directory contains a fuzz test for the FastPFOR compression codec to find bugs, panics, and data corruption issues.
+This directory contains fuzz tests for the FastPFOR compression codec to find bugs, panics, and data corruption issues.
 
 ## Why Fuzz FastPFOR?
 
-The FastPFOR codec is the core compression algorithm. Fuzzing helps catch:
-- Data corruption during compress/decompress roundtrips
+The FastPFOR codec is a core compression algorithm. Fuzzing helps catch:
+- Implementation discrepancies between Rust and C++
+- Data corruption during compress/decompress cycles
 - Panics on edge case inputs
 - Buffer overflows or underflows
 - Incorrect handling of different block sizes (128 vs 256)
 - Issues with boundary conditions (empty data, very large values, etc.)
 
-## Known Issues Found
-
-The fuzzer has already discovered the following issues:
-
-### Data Loss with Small Inputs (Issue #1)
-
-**Input:** Single element array `[0]` with block size 128
-
-**Issue:** FastPFOR silently drops data that doesn't fit into complete blocks. When the input length is less than the block size (128 or 256), `greatest_multiple(input_length, block_size)` returns 0, causing the codec to:
-1. Write 0 to the output header
-2. Skip compression entirely
-3. On decompression, return 0 elements instead of the original input
-
-**Expected:** Should either:
-- Compress partial blocks correctly, or
-- Return an error indicating input is too small, or
-- Document this limitation clearly
-
-This is a **data corruption bug** where the codec claims success but loses data.
-
 ## Prerequisites
 
 Install cargo-fuzz and switch to nightly Rust:
@@ -40,34 +21,41 @@ cargo install cargo-fuzz
 rustup install nightly
 ```
 
-## Running the Fuzzer
+## Running the Fuzzers
+
+Run the oracle-based compression fuzzer:
 
 ```bash
 cd fuzz
-cargo +nightly fuzz run fastpfor_rust
+cargo +nightly fuzz run rust_compress_oracle
+# or
+cargo +nightly fuzz run rust_decompress_oracle
+# or
+cargo +nightly fuzz run cpp_roundtrip
 ```
 
 Run for a specific duration (e.g., 60 seconds):
 
 ```bash
-cargo +nightly fuzz run fastpfor_rust -- -max_total_time=60
+cargo +nightly fuzz run rust_compress_oracle -- -max_total_time=60
 ```
 
-## What It Tests
+Run with specific number of iterations:
 
-The fuzzer:
-1. Generates random sequences of u32 integers
-2. Randomly selects block size (128 or 256)
-3. Compresses the data with FastPFOR
-4. Decompresses the result
-5. Verifies the output matches the original input exactly
-
-This ensures the codec is lossless and doesn't corrupt data under any input pattern.
+```bash
+cargo +nightly fuzz run rust_compress_oracle -- -runs=1000
+```
 
 ## If a Crash Is Found
 
-Crashes are saved to `fuzz/artifacts/fastpfor_rust/`. To reproduce:
+Crashes are saved to `fuzz/artifacts/<target_name>/`. To reproduce:
+
+```bash
+cargo +nightly fuzz run <target_name> fuzz/artifacts/<target_name>/crash-<hash>
+```
+
+For example:
 
 ```bash
-cargo +nightly fuzz run fastpfor_rust fuzz/artifacts/fastpfor_rust/crash-<hash>
+cargo +nightly fuzz run rust_compress_oracle fuzz/artifacts/rust_compress_oracle/crash-abc123
 ```

fuzz/fuzz_targets/common.rs

@@ -0,0 +1,119 @@
+use fastpfor::cpp;
+use fastpfor::rust;
+
+pub type BoxedCppCodec = Box<dyn cpp::Codec32>;
+
+#[derive(arbitrary::Arbitrary)]
+pub struct FuzzInput<C> {
+    pub data: Vec<u32>,
+    pub codec: C,
+}
+
+impl<C: std::fmt::Debug> std::fmt::Debug for FuzzInput<C> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("FuzzInput<C>")
+            .field("data_length", &self.data.len())
+            .field("codec", &self.codec)
+            .finish()
+    }
+}
+
+#[derive(arbitrary::Arbitrary, Clone, Copy, PartialEq, Eq, Debug)]
+pub enum RustCodec {
+    FastPFOR256,
+    FastPFOR128,
+    VariableByte,
+    JustCopy,
+}
+
+impl From<RustCodec> for rust::Codec {
+    fn from(codec: RustCodec) -> Self {
+        use rust::*;
+        match codec {
+            RustCodec::FastPFOR256 => Codec::from(FastPFOR::new(DEFAULT_PAGE_SIZE, BLOCK_SIZE_256)),
+            RustCodec::FastPFOR128 => Codec::from(FastPFOR::new(DEFAULT_PAGE_SIZE, BLOCK_SIZE_128)),
+            RustCodec::VariableByte => Codec::from(VariableByte::new()),
+            RustCodec::JustCopy => Codec::from(JustCopy::new()),
+        }
+    }
+}
+
+#[derive(Clone, Copy, Eq, PartialEq, arbitrary::Arbitrary, Debug)]
+pub enum CppCodec {
+    BP32,
+    Copy,
+    FastBinaryPacking8,
+    FastPFor128,
+    FastPFor256,
+    FastBinaryPacking16,
+    FastBinaryPacking32,
+    MaskedVByte,
+    NewPFor,
+    OptPFor,
+    PFor2008,
+    PFor,
+    SimdBinaryPacking,
+    SimdFastPFor128,
+    SimdFastPFor256,
+    SimdGroupSimple,
+    SimdGroupSimpleRingBuf,
+    SimdNewPFor,
+    SimdOptPFor,
+    SimdPFor,
+    SimdSimplePFor,
+    // Simple16, // cannot encode arbitrary bytes
+    // Simple8b, // cannot encode arbitrary bytes
+    // Simple8bRle, // cannot encode arbitrary bytes
+    // Simple9, // cannot encode arbitrary bytes
+    // Simple9Rle, // cannot encode arbitrary bytes
+    // SimplePFor, // cannot encode arbitrary bytes
+    // Snappy,  // Conditional with #ifdef
+    StreamVByte,
+    VByte,
+    VarInt,
+    // VarIntG8iu,  // Conditional with #ifdef
+    VarIntGb,
+    // VsEncoding,  // This is leaking memory
+}
+
+impl From<CppCodec> for BoxedCppCodec {
+    fn from(codec: CppCodec) -> Self {
+        use cpp::*;
+        match codec {
+            CppCodec::BP32 => Box::new(BP32Codec::default()),
+            CppCodec::Copy => Box::new(CopyCodec::default()),
+            CppCodec::FastBinaryPacking8 => Box::new(FastBinaryPacking8Codec::default()),
+            CppCodec::FastPFor128 => Box::new(FastPFor128Codec::default()),
+            CppCodec::FastPFor256 => Box::new(FastPFor256Codec::default()),
+            CppCodec::FastBinaryPacking16 => Box::new(FastBinaryPacking16Codec::default()),
+            CppCodec::FastBinaryPacking32 => Box::new(FastBinaryPacking32Codec::default()),
+            CppCodec::MaskedVByte => Box::new(MaskedVByteCodec::default()),
+            CppCodec::NewPFor => Box::new(NewPForCodec::default()),
+            CppCodec::OptPFor => Box::new(OptPForCodec::default()),
+            CppCodec::PFor2008 => Box::new(PFor2008Codec::default()),
+            CppCodec::PFor => Box::new(PForCodec::default()),
+            CppCodec::SimdBinaryPacking => Box::new(SimdBinaryPackingCodec::default()),
+            CppCodec::SimdFastPFor128 => Box::new(SimdFastPFor128Codec::default()),
+            CppCodec::SimdFastPFor256 => Box::new(SimdFastPFor256Codec::default()),
+            CppCodec::SimdGroupSimple => Box::new(SimdGroupSimpleCodec::default()),
+            CppCodec::SimdGroupSimpleRingBuf => Box::new(SimdGroupSimpleRingBufCodec::default()),
+            CppCodec::SimdNewPFor => Box::new(SimdNewPForCodec::default()),
+            CppCodec::SimdOptPFor => Box::new(SimdOptPForCodec::default()),
+            CppCodec::SimdPFor => Box::new(SimdPForCodec::default()),
+            CppCodec::SimdSimplePFor => Box::new(SimdSimplePForCodec::default()),
+            // CppCodec::Simple16 => Box::new(Simple16Codec::default()),
+            // CppCodec::Simple8b => Box::new(Simple8bCodec::default()),
+            // CppCodec::Simple8bRle => Box::new(Simple8bRleCodec::default()),
+            // CppCodec::Simple9 => Box::new(Simple9Codec::default()),
+            // CppCodec::Simple9Rle => Box::new(Simple9RleCodec::default()),
+            // CppCodec::SimplePFor => Box::new(SimplePForCodec::default()),
+            // CppCodec::Snappy => Box::new(SnappyCodec::default()),
+            CppCodec::StreamVByte => Box::new(StreamVByteCodec::default()),
+            CppCodec::VByte => Box::new(VByteCodec::default()),
+            CppCodec::VarInt => Box::new(VarIntCodec::default()),
+            // CppCodec::VarIntG8iu => Box::new(VarIntG8iuCodec::default()),
+            CppCodec::VarIntGb => Box::new(VarIntGbCodec::default()),
+            // CppCodec::VsEncoding => Box::new(VsEncodingCodec::default()),
+        }
+    }
+}

fuzz/fuzz_targets/cpp_roundtrip.rs

@@ -0,0 +1,33 @@
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+mod common;
+use common::*;
+
+fuzz_target!(|data: FuzzInput<CppCodec>| {
+    let codec = BoxedCppCodec::from(data.codec);
+    let input = data.data;
+
+    // Allocate output buffer with generous size
+    let mut output = vec![0u32; input.len() * 2 + 1024];
+
+    // Compress the data
+    let enc_slice = codec.encode32(&input, &mut output).unwrap();
+
+    // Now decompress
+    let mut decoded = vec![0u32; input.len() * 2 + 1024];
+    let dec_slice = codec.decode32(enc_slice, &mut decoded).unwrap();
+
+    // Verify roundtrip
+    if dec_slice.len() + input.len() < 200 {
+        assert_eq!(input, dec_slice, "Decompressed output mismatches");
+    } else {
+        assert_eq!(dec_slice.len(), input.len(), "Decompressed length mismatch");
+        for (i, (&original, &decoded)) in input.iter().zip(dec_slice.iter()).enumerate() {
+            assert_eq!(
+                original, decoded,
+                "Mismatch at position {i}: expected {original}, got {decoded}"
+            );
+        }
+    }
+});