Address some PR review comments

Author: ros-cr

fuzz/Cargo.toml

@@ -18,6 +18,7 @@ rust-allocator = ["libbz2-rs-sys/rust-allocator"]
 disable-checksum = ["libbz2-rs-sys/__internal-fuzz-disable-checksum"]
 # actively reject and ignore invalid fuzz inputs during processing
 # this can have negative effects
+# see the README.md for more information
 reject-invalid-in-corpus = [] 
 
 [dependencies.libfuzzer-sys]

fuzz/README.md

@@ -1,5 +1,23 @@
 # Fuzz
 
+## Corpus input rejection mode
+
+libFuzzer has [an optional mechanism](https://llvm.org/docs/LibFuzzer.html#rejecting-unwanted-inputs) to explicitly reject fuzz inputs.
+This directive forces the fuzzer to forget the observed coverage for the current input, and does not allow adding it to the corpus collection.
+
+
+Use the custom `--features reject-invalid-in-corpus` crate feature to enable this logic in the fuzz harnesses that make use of it. The flag is optional and off by default, see `Cargo.toml`.
+
+This is a heavy-handed approach and reduces fuzzer coverage visibility into the rejected code paths, 
+but may be useful for time-constrained runs.
+
+Expected effects:
+1. reduce some runtime overhead on rejected inputs by skipping post-processing steps
+2. increases ratio of "valid" inputs in working corpus
+
+The expectation is that this makes it more likely to create valid inputs by mutation, 
+at least on short runs with a limited amount of executions that start on a pre-seeded corpus.
+
 ## Seed corpus
 
 * https://github.com/trifectatechfoundation/compression-corpus
@@ -8,7 +26,7 @@
 
 ## Fuzzer dictionary
 
-* There is an existing bzip2 format dictionary: https://github.com/google/fuzzing/blob/master/dictionaries/bz2.dict
+* There is an existing bzip2 format fuzz dictionary: https://github.com/google/fuzzing/blob/master/dictionaries/bz2.dict
 * This could be useful for fuzz tests which consume compressed input and attempt to decompress it
 * However, there are only very few common input chunks that bzip2 streams share with each other, so the practical benefits of running the fuzzer with this dictionary is likely limited
 * See https://llvm.org/docs/LibFuzzer.html#dictionaries for more background

fuzz/fuzz_targets/compress_then_decompress_chunked.rs

@@ -11,8 +11,8 @@ use libbz2_rs_sys::{
 
 use libfuzzer_sys::fuzz_target;
 
+/// compress the data with the stock C bzip2
 fn compress_c(data: &[u8], compression_level: u8, work_factor: u8) -> Vec<u8> {
-    // compress the data with the stock C bzip2
 
     // output buffer for compression, will get resized later if needed
     let mut output = vec![0u8; 1024];

fuzz/fuzz_targets/decompress.rs

@@ -12,11 +12,9 @@ fuzz_target!(|fuzz_data: &[u8]| {
         test_libbz2_rs_sys::decompress_rs_with_capacity(1 << 12, fuzz_data.as_ptr(), fuzz_data.len() as _)
     };
 
-    // ignore known edge case with different error result behavior
-    if err_c != -7 && err_rs != -4 {
-        // in the general case, result codes should be identical
-        assert_eq!(err_c, err_rs);
-    }
+    // result codes between the two implementations should be identical
+    // previously found https://github.com/trifectatechfoundation/libbzip2-rs/pull/110
+    assert_eq!(err_c, err_rs);
 
     // if the decompression is successful, the data results should be the same
     if err_c == BZ_OK {

fuzz/fuzz_targets/decompress_chunked.rs

@@ -99,18 +99,10 @@ fuzz_target!(|fuzz_data: &[u8]| -> Corpus {
                     // stop processing
                     return invalid_input;
                 }
-                BZ_FLUSH_OK => {
-                    panic!("BZ_FLUSH_OK");
-                }
-                BZ_RUN_OK => {
-                    panic!("BZ_RUN_OK");
-                }
-                BZ_FINISH_OK => {
-                    panic!("BZ_FINISH_OK");
-                }
-                BZ_OUTBUFF_FULL => {
-                    panic!("BZ_OUTBUFF_FULL");
-                }
+                BZ_FLUSH_OK => panic!("BZ_FLUSH_OK"),
+                BZ_RUN_OK => panic!("BZ_RUN_OK"),
+                BZ_FINISH_OK => panic!("BZ_FINISH_OK"),
+                BZ_OUTBUFF_FULL => panic!("BZ_OUTBUFF_FULL"),
                 err => panic!("{err}"),
             }
         }