38 lines
1.2 KiB
Markdown
38 lines
1.2 KiB
Markdown
# SQ-005: WAL Segment Reader
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**Status:** `[ ] TODO`
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**Blocked by:** SQ-004
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**Priority:** High
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## Description
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Implement the WAL segment reader that reads messages from segment files, supporting seek-to-offset and forward scanning.
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## Files to Create/Modify
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- `crates/sq-storage/src/wal/reader.rs` - WalReader with open, read_from, iterator
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## WalReader API
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```rust
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pub struct WalReader<F: FileSystem> {
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fs: Arc<F>,
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}
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impl<F: FileSystem> WalReader<F> {
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pub fn new(fs: Arc<F>) -> Self;
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pub async fn read_segment(&self, path: &Path) -> Result<Vec<Message>>;
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pub async fn read_from_offset(&self, path: &Path, offset: u64) -> Result<Vec<Message>>;
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pub async fn read_segment_header(&self, path: &Path) -> Result<SegmentHeader>;
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}
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```
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## Acceptance Criteria (using InMemoryFileSystem)
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- [ ] Write N messages with writer, read all back with reader, verify equality
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- [ ] Read from a specific offset in the middle of a segment
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- [ ] Corrupted record mid-segment: reader returns error for that record, can report partial results
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- [ ] Empty segment (header only): reader yields zero messages
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- [ ] Invalid magic bytes: reader returns descriptive error
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- [ ] Truncated record at end of segment (partial write): reader stops cleanly at last complete record
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