commitlog: Fix single-commit bitflip test (#1528)

crates/commitlog/proptest-regressions/commit.txt

@@ -0,0 +1,13 @@
+# Seeds for failure cases proptest has generated in the past. It is
+# automatically read and these particular cases re-run before any
+# novel cases are generated.
+#
+# It is recommended to check this file in to source control so that
+# everyone who runs the test benefits from these saved cases.
+cc 99379dfa7ddc8e9547aef6261c7ed937bd6d100950ceab6dfb3b2c819d5e5eb2 # shrinks to mask = 147
+cc d7996990b19364fdd507c75b6eab42c966200a9a87c1cf20b0d525e943707028 # shrinks to mask = 0
+cc 90f9c1e55a9e1a0b6239a493778d94a99c483a96b142214ff068d08a59587474 # shrinks to mask = 234
+cc d98894bc4f25542121d91f3022916c5e140fea25834dde209a001232a7a3a122 # shrinks to mask = 54
+cc 893c2bb61cc7c758ac3b6f36485ee8789e6ed6f92ecc531ca9622e9b0e23a5d0 # shrinks to mask = 183
+cc ca54db4fcdc0af1fe3c039f58b43b6f51c065120851261bdd495c8e0afed60bd # shrinks to mask = 10
+cc 3dc841d9145fa0f6abec7fbb37fec26d47c223b00d59cf2f67ad9ee79fcab728 # shrinks to mask = 166

crates/commitlog/src/commit.rs

@@ -265,7 +265,9 @@ where
 
 #[cfg(test)]
 mod tests {
-    use rand::prelude::*;
+    use std::num::NonZeroU8;
+
+    use proptest::prelude::*;
 
     use super::*;
 
@@ -285,30 +287,32 @@ mod tests {
         assert_eq!(commit, commit2);
     }
 
-    #[test]
-    fn bitflip() {
-        let commit = Commit {
-            min_tx_offset: 42,
-            n: 10,
-            records: vec![1; 512],
-        };
+    proptest! {
+        #[test]
+        fn bitflip(pos in Header::LEN..512, mask in any::<NonZeroU8>()) {
+            let commit = Commit {
+                min_tx_offset: 42,
+                n: 10,
+                records: vec![1; 512],
+            };
 
-        let mut buf = Vec::with_capacity(commit.encoded_len());
-        commit.write(&mut buf).unwrap();
+            let mut buf = Vec::with_capacity(commit.encoded_len());
+            commit.write(&mut buf).unwrap();
 
-        let mut rng = thread_rng();
-        let b = buf.choose_mut(&mut rng).unwrap();
-        *b ^= rng.gen::<u8>();
+            // Flip bit in the `records` section,
+            // so we get `ChecksumMismatch` not any other error.
+            buf[pos] ^= mask.get();
 
-        match Commit::decode(&mut buf.as_slice()) {
-            Err(e) => {
-                assert_eq!(e.kind(), io::ErrorKind::InvalidData);
-                e.into_inner()
-                    .unwrap()
-                    .downcast::<ChecksumMismatch>()
-                    .expect("IO inner should be checksum mismatch");
+            match Commit::decode(&mut buf.as_slice()) {
+                Err(e) => {
+                    assert_eq!(e.kind(), io::ErrorKind::InvalidData);
+                    e.into_inner()
+                        .unwrap()
+                        .downcast::<ChecksumMismatch>()
+                        .expect("IO inner should be checksum mismatch");
+                }
+                Ok(commit) => panic!("expected checksum mismatch, got valid commit: {commit:?}"),
             }
-            Ok(commit) => panic!("expected checksum mismatch, got valid commit: {commit:?}"),
         }
     }
 }