fix: audit fixes for 4 medium-severity bugs: index_cache tail hash, read_cache doc, mutex poison recovery, Remove event handling

crates/core/src/io/index_cache.rs

@@ -86,11 +86,12 @@ fn compute_file_hash(file_path: &Path) -> std::io::Result<u64> {
         let mut tf = std::io::BufReader::new(file);
         tf.read_exact(&mut tail)?;
     } else {
-        // File is small enough that head already covers everything;
-        // tail overlaps with head — just take the last tail_size bytes
-        let start = head.len().saturating_sub(tail_size);
-        tail = head[start..].to_vec();
-        tail.resize(tail_size, 0);
+        // File fits within head+tail window. Seek to read the real tail
+        // for correctness — approximating from head misses bytes beyond head_size.
+        let tail_start = file_size.saturating_sub(tail_size as u64);
+        let mut file = std::fs::File::open(file_path)?;
+        std::io::Seek::seek(&mut file, std::io::SeekFrom::Start(tail_start))?;
+        file.read_exact(&mut tail)?;
     }
 
     let mut hasher_state = xxhash_rust::xxh3::Xxh3::new();

crates/core/src/io/read_cache.rs

@@ -0,0 +1,435 @@
+// NOTE: This module is implemented and tested but not yet integrated into
+// the production read path (FileReader uses mmap for line access).
+// It is kept as a building block for a future pread-based reader that
+// would avoid the SIGBUS risk of mmap.
+// ─── read_cache.rs ─────────────────────────────────────────────────────────
+// 16-slot LRU read cache with 4KB page-aligned keys.
+// Reduces syscalls by caching recently-read 4KB blocks.
+// Cross-block reads are handled via a spill buffer (not cached).
+// ──────────────────────────────────────────────────────────────────────────
+
+use std::fs::File;
+use std::io;
+use std::os::unix::fs::FileExt;
+
+const LRU_SLOTS: usize = 16;
+pub const BLOCK_ALIGN: usize = 4096;
+
+struct CacheSlot {
+    buf: Vec<u8>,
+    block_offset: u64,
+    len: usize,
+    last_access: u64,
+}
+
+pub struct LruReadCache {
+    slots: [CacheSlot; LRU_SLOTS],
+    spill_buf: Vec<u8>,
+    spill_len: usize,
+    tick: u64,
+}
+
+pub type ReadCache = LruReadCache;
+
+impl Default for LruReadCache {
+    fn default() -> Self {
+        Self {
+            slots: std::array::from_fn(|_| CacheSlot {
+                buf: vec![0u8; BLOCK_ALIGN],
+                block_offset: 0,
+                len: 0,
+                last_access: 0,
+            }),
+            spill_buf: Vec::new(),
+            spill_len: 0,
+            tick: 0,
+        }
+    }
+}
+
+impl LruReadCache {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Read `len` bytes starting at `offset`. Returns a slice into the cache
+    /// on a hit, or fills a cache slot on a miss. Cross-block reads go through
+    /// the spill buffer and are not cached.
+    pub fn get(&mut self, file: &File, offset: u64, len: usize) -> io::Result<&[u8]> {
+        let aligned_key = offset & !(BLOCK_ALIGN as u64 - 1);
+        let request_end = offset.saturating_add(len as u64);
+        let block_end = aligned_key + BLOCK_ALIGN as u64;
+
+        if request_end > block_end {
+            self.spill_buf.resize(len, 0);
+            let bytes_read = file.read_at(&mut self.spill_buf[..len], offset)?;
+            if bytes_read == 0 {
+                return Err(io::Error::new(io::ErrorKind::UnexpectedEof, "read 0 bytes"));
+            }
+            if bytes_read < len {
+                return Err(io::Error::new(io::ErrorKind::UnexpectedEof, "short read"));
+            }
+            self.spill_len = len;
+            return Ok(&self.spill_buf[..len]);
+        }
+
+        let hit_idx = self.slots.iter().position(|slot| {
+            slot.block_offset == aligned_key && request_end <= slot.block_offset + slot.len as u64
+        });
+
+        if let Some(idx) = hit_idx {
+            self.slots[idx].last_access = self.tick;
+            self.tick += 1;
+            let start = (offset - self.slots[idx].block_offset) as usize;
+            return Ok(&self.slots[idx].buf[start..start + len]);
+        }
+
+        let mut evict_idx = 0;
+        let mut min_access = self.slots[0].last_access;
+        for (i, slot) in self.slots.iter().enumerate() {
+            if slot.last_access < min_access {
+                min_access = slot.last_access;
+                evict_idx = i;
+            }
+        }
+
+        let slot = &mut self.slots[evict_idx];
+        let bytes_read = file.read_at(&mut slot.buf, aligned_key)?;
+
+        // Note: get(file, 0, 0) on an empty file now returns Err (old code returned Ok(&[])).
+        // No callers pass len == 0, so this is a safe semantic change.
+        if bytes_read == 0 {
+            return Err(io::Error::new(io::ErrorKind::UnexpectedEof, "read 0 bytes"));
+        }
+
+        slot.block_offset = aligned_key;
+        slot.len = bytes_read;
+        slot.last_access = self.tick;
+        self.tick += 1;
+
+        if request_end > aligned_key + bytes_read as u64 {
+            return Err(io::Error::new(io::ErrorKind::UnexpectedEof, "short read"));
+        }
+
+        let start = (offset - slot.block_offset) as usize;
+        Ok(&slot.buf[start..start + len])
+    }
+
+    /// Invalidate all cache slots and the spill buffer.
+    pub fn clear(&mut self) {
+        for slot in &mut self.slots {
+            slot.len = 0;
+        }
+        self.spill_len = 0;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::Write;
+    use tempfile::NamedTempFile;
+
+    fn make_file(data: &[u8]) -> NamedTempFile {
+        let mut f = NamedTempFile::new().unwrap();
+        f.write_all(data).unwrap();
+        f.flush().unwrap();
+        f
+    }
+
+    #[test]
+    fn cache_hit_returns_same_data() {
+        // Read the same range twice — second read should be a cache hit.
+        let f = make_file(b"Hello, World! This is a test of the cache.");
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let first = cache.get(&file, 0, 13).unwrap().to_vec();
+        let second = cache.get(&file, 0, 13).unwrap().to_vec();
+        assert_eq!(first, second);
+        assert_eq!(&first, b"Hello, World!");
+    }
+
+    #[test]
+    fn cache_miss_reads_correct_data() {
+        // Two non-overlapping ranges — both must be misses but return correct data.
+        let data = b"0123456789ABCDEFGHIJ";
+        let f = make_file(data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let a = cache.get(&file, 0, 10).unwrap().to_vec();
+        assert_eq!(&a, b"0123456789");
+
+        let b = cache.get(&file, 10, 10).unwrap().to_vec();
+        assert_eq!(&b, b"ABCDEFGHIJ");
+    }
+
+    #[test]
+    fn cross_block_read_uses_spill_buffer() {
+        // Read spanning a 4KB block boundary uses spill buffer, not cache.
+        let data = vec![0xABu8; 8192];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // First, cache block 0.
+        let a = cache.get(&file, 0, 100).unwrap().to_vec();
+        assert_eq!(a, vec![0xABu8; 100]);
+
+        // Now read spanning the boundary: offset=4000, len=200 spans [0,4096) and [4096,8192).
+        let b = cache.get(&file, 4000, 200).unwrap().to_vec();
+        assert_eq!(b, vec![0xABu8; 200]);
+    }
+
+    #[test]
+    fn empty_file_read_fails() {
+        let f = make_file(b"");
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Reading 1 byte from empty file should fail.
+        let result = cache.get(&file, 0, 1);
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn clear_invalidates_cache() {
+        let data = b"original data here";
+        let f = make_file(data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Populate cache.
+        let first = cache.get(&file, 0, 10).unwrap().to_vec();
+        assert_eq!(&first, b"original d");
+
+        // Invalidate.
+        cache.clear();
+
+        // After clear, reading same range should still work (re-reads from file).
+        let after = cache.get(&file, 0, 10).unwrap().to_vec();
+        assert_eq!(&after, b"original d");
+    }
+
+    // ─── New LRU-specific tests ───────────────────────────────────────────
+
+    #[test]
+    fn lru_multi_block_hit() {
+        // Read 3 different aligned blocks, verify re-reading each hits cache.
+        let data = vec![0u8; BLOCK_ALIGN * 4];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Write distinct patterns to each block.
+        drop(file);
+        {
+            use std::io::Seek;
+            let mut f2 = std::fs::OpenOptions::new()
+                .write(true)
+                .open(f.path())
+                .unwrap();
+            f2.seek(std::io::SeekFrom::Start(0)).unwrap();
+            f2.write_all(&[1u8; BLOCK_ALIGN]).unwrap();
+            f2.seek(std::io::SeekFrom::Start(BLOCK_ALIGN as u64))
+                .unwrap();
+            f2.write_all(&[2u8; BLOCK_ALIGN]).unwrap();
+            f2.seek(std::io::SeekFrom::Start((BLOCK_ALIGN * 2) as u64))
+                .unwrap();
+            f2.write_all(&[3u8; BLOCK_ALIGN]).unwrap();
+        }
+        let file = File::open(f.path()).unwrap();
+
+        let block0 = cache.get(&file, 0, 16).unwrap().to_vec();
+        let block1 = cache.get(&file, BLOCK_ALIGN as u64, 16).unwrap().to_vec();
+        let block2 = cache
+            .get(&file, (BLOCK_ALIGN * 2) as u64, 16)
+            .unwrap()
+            .to_vec();
+
+        assert_eq!(block0, vec![1u8; 16]);
+        assert_eq!(block1, vec![2u8; 16]);
+        assert_eq!(block2, vec![3u8; 16]);
+
+        // Re-read — should hit cache and return same data.
+        let block0_again = cache.get(&file, 0, 16).unwrap().to_vec();
+        let block1_again = cache.get(&file, BLOCK_ALIGN as u64, 16).unwrap().to_vec();
+        let block2_again = cache
+            .get(&file, (BLOCK_ALIGN * 2) as u64, 16)
+            .unwrap()
+            .to_vec();
+
+        assert_eq!(block0_again, block0);
+        assert_eq!(block1_again, block1);
+        assert_eq!(block2_again, block2);
+    }
+
+    #[test]
+    fn lru_eviction_order() {
+        // Fill all 16 slots, re-access slot 0, add 17th block,
+        // verify slot at offset 4096 (slot 1) evicted, not slot 0.
+        let data = vec![0u8; BLOCK_ALIGN * 20];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Fill all 16 slots with blocks 0..16.
+        for i in 0..16u64 {
+            cache.get(&file, i * BLOCK_ALIGN as u64, 1).unwrap();
+        }
+
+        // Re-access block 0 so it's not the LRU.
+        cache.get(&file, 0, 1).unwrap();
+
+        // Add 17th block — should evict block 1 (offset 4096), which is the oldest
+        // since block 0 was re-accessed.
+        cache.get(&file, 16 * BLOCK_ALIGN as u64, 1).unwrap();
+
+        // Reading block 1 (offset 4096) should be a miss (evicted).
+        // We verify by checking the cache slots: block 1 should not be cached.
+        let has_block1 = cache
+            .slots
+            .iter()
+            .any(|s| s.block_offset == BLOCK_ALIGN as u64 && s.len > 0);
+        assert!(!has_block1, "block 1 should have been evicted");
+
+        // Block 0 should still be cached.
+        let has_block0 = cache.slots.iter().any(|s| s.block_offset == 0 && s.len > 0);
+        assert!(has_block0, "block 0 should still be cached");
+    }
+
+    #[test]
+    fn lru_clear_all_slots() {
+        // Fill 3+ slots, call clear(), verify subsequent reads all miss.
+        let data = vec![0x42u8; BLOCK_ALIGN * 4];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Fill 3 slots.
+        cache.get(&file, 0, 1).unwrap();
+        cache.get(&file, BLOCK_ALIGN as u64, 1).unwrap();
+        cache.get(&file, (BLOCK_ALIGN * 2) as u64, 1).unwrap();
+
+        cache.clear();
+
+        // All slots should have len == 0.
+        for slot in &cache.slots {
+            assert_eq!(slot.len, 0);
+        }
+        assert_eq!(cache.spill_len, 0);
+
+        // Re-read should still work (reads from file).
+        let val = cache.get(&file, 0, 1).unwrap();
+        assert_eq!(val[0], 0x42);
+    }
+
+    #[test]
+    fn lru_aligned_keys() {
+        // offset=100 and offset=200 both align to block 0 — should hit same slot.
+        let data = vec![0xEEu8; BLOCK_ALIGN];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let a = cache.get(&file, 100, 10).unwrap().to_vec();
+        assert_eq!(a, vec![0xEEu8; 10]);
+
+        let b = cache.get(&file, 200, 10).unwrap().to_vec();
+        assert_eq!(b, vec![0xEEu8; 10]);
+
+        // Both should be served from the same cache slot (block 0).
+        let slot_count = cache
+            .slots
+            .iter()
+            .filter(|s| s.block_offset == 0 && s.len > 0)
+            .count();
+        assert_eq!(slot_count, 1, "only one slot should hold block 0");
+    }
+
+    #[test]
+    fn lru_cross_block_uses_spill_buffer() {
+        // File [0xAA×4096, 0xBB×4096], get(file, 4090, 20) → [0xAA×6, 0xBB×14].
+        let mut data = vec![0xAAu8; BLOCK_ALIGN];
+        data.extend_from_slice(&vec![0xBBu8; BLOCK_ALIGN]);
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let result = cache.get(&file, 4090, 20).unwrap().to_vec();
+        assert_eq!(&result[..6], &[0xAAu8; 6]);
+        assert_eq!(&result[6..], &[0xBBu8; 14]);
+
+        // Verify no cache slot holds block 0 or block 1.
+        for slot in &cache.slots {
+            assert!(
+                slot.len == 0,
+                "cross-block data should not be cached in slots"
+            );
+        }
+    }
+
+    #[test]
+    fn lru_partial_last_block() {
+        // 5000 byte file, get(file, 4096, 904) reads last 904 bytes,
+        // then get(file, 4096, 100) hits cache.
+        let data = vec![0x77u8; 5000];
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let first = cache.get(&file, 4096, 904).unwrap().to_vec();
+        assert_eq!(first.len(), 904);
+        assert_eq!(first, vec![0x77u8; 904]);
+
+        // Second read of 100 bytes from same block should hit cache.
+        let second = cache.get(&file, 4096, 100).unwrap().to_vec();
+        assert_eq!(second.len(), 100);
+        assert_eq!(second, vec![0x77u8; 100]);
+    }
+
+    #[test]
+    fn lru_short_file_overread() {
+        // 1 byte file, get(file, 0, 100) → Err (not panic).
+        let f = make_file(b"X");
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let result = cache.get(&file, 0, 100);
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn lru_empty_file_returns_error() {
+        // Empty file, get(file, 0, 1) → Err.
+        let f = make_file(b"");
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        let result = cache.get(&file, 0, 1);
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn long_line_spans_multiple_blocks() {
+        // Create file with line >4KB: b'A'×4090 + "\n" + b'B'×4090 + "\n"
+        let mut data = vec![b'A'; 4090];
+        data.push(b'\n');
+        data.extend_from_slice(&vec![b'B'; 4090]);
+        data.push(b'\n');
+        let f = make_file(&data);
+        let file = File::open(f.path()).unwrap();
+        let mut cache = ReadCache::new();
+
+        // Read the first line: offset 0, len 4091 (fits in block 0 since 4091 <= 4096).
+        let line1 = cache.get(&file, 0, 4091).unwrap().to_vec();
+        assert_eq!(&line1[..4090], &[b'A'; 4090]);
+        assert_eq!(line1[4090], b'\n');
+
+        // Read the second line: offset 4091, len 4091 (starts in block 0, ends in block 1 — cross-block).
+        let line2 = cache.get(&file, 4091, 4091).unwrap().to_vec();
+        assert_eq!(&line2[..4090], &[b'B'; 4090]);
+        assert_eq!(line2[4090], b'\n');
+    }
+}

crates/core/src/watcher/file_watcher.rs

@@ -12,6 +12,7 @@ pub enum FileEvent {
     Appended { new_size: u64 },
     Truncated { new_size: u64 },
     Rotated { new_inode: u64 },
+    Removed,
 }
 
 // ─── get_inode ──────────────────────────────────────────────────────────────
@@ -60,6 +61,10 @@ impl FileWatcher {
 
                 match event.kind {
                     EventKind::Modify(_) | EventKind::Create(_) | EventKind::Any => {}
+                    EventKind::Remove(_) => {
+                        let _ = tx.send(FileEvent::Removed);
+                        return;
+                    }
                     _ => return,
                 }
 
@@ -70,7 +75,12 @@ impl FileWatcher {
                 let current_inode = get_inode(&watch_path).unwrap_or(0);
                 let current_size = std::fs::metadata(&watch_path).map(|m| m.len()).unwrap_or(0);
 
-                let mut st = state.lock().unwrap();
+                let mut st = state.lock().unwrap_or_else(|poison| {
+                    // Recover from poisoned mutex — state only tracks last_size
+                    // and last_inode for event dedup. Stale values at worst
+                    // cause a duplicate event, which is harmless.
+                    poison.into_inner()
+                });
 
                 if current_inode != 0 && st.last_inode != 0 && current_inode != st.last_inode {
                     let _ = tx.send(FileEvent::Rotated {

crates/tui/src/app.rs

@@ -848,6 +848,9 @@ impl App {
                     // Don't auto-switch; old content preserved.
                     // User can reload manually if desired.
                 }
+                FileEvent::Removed => {
+                    self.loading_state = AppLoadingState::Error("File has been deleted".into());
+                }
             }
         }
     }