feat(code): part 3 iterators

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm/src/mem_table.rs

@@ -0,0 +1,110 @@
+use std::ops::Bound;
+
+use anyhow::Result;
+use bytes::Bytes;
+use crossbeam_skiplist::map::Entry;
+use crossbeam_skiplist::SkipMap;
+
+use crate::iterators::impls::StorageIterator;
+use crate::table::SsTableBuilder;
+
+/// A basic mem-table based on crossbeam-skiplist
+pub struct MemTable {
+    map: SkipMap<Bytes, Bytes>,
+}
+
+impl MemTable {
+    /// Create a new mem-table.
+    pub fn create() -> Self {
+        Self {
+            map: SkipMap::new(),
+        }
+    }
+
+    /// Get a value by key.
+    pub fn get(&self, key: &[u8]) -> Result<Option<Bytes>> {
+        let entry = self.map.get(key).map(|e| e.value().clone());
+        Ok(entry)
+    }
+
+    /// Put a key-value pair into the mem-table.
+    pub fn put(&self, key: &[u8], value: &[u8]) -> Result<()> {
+        self.map
+            .insert(Bytes::copy_from_slice(key), Bytes::copy_from_slice(value));
+        Ok(())
+    }
+
+    fn map_bound(bound: Bound<&[u8]>) -> Bound<Bytes> {
+        match bound {
+            Bound::Included(x) => Bound::Included(Bytes::copy_from_slice(x)),
+            Bound::Excluded(x) => Bound::Excluded(Bytes::copy_from_slice(x)),
+            Bound::Unbounded => Bound::Unbounded,
+        }
+    }
+
+    /// Get an iterator over a range of keys.
+    pub fn scan(&self, lower: Bound<&[u8]>, upper: Bound<&[u8]>) -> Result<MemTableIterator> {
+        let iter = self
+            .map
+            .range((Self::map_bound(lower), Self::map_bound(upper)));
+        Ok(MemTableIterator::new(iter))
+    }
+
+    /// Flush the mem-table to SSTable.
+    pub fn flush(&self, builder: &mut SsTableBuilder) -> Result<()> {
+        for entry in self.map.iter() {
+            builder.add(&entry.key()[..], &entry.value()[..]);
+        }
+        Ok(())
+    }
+}
+
+type SkipMapRangeIter<'a> =
+    crossbeam_skiplist::map::Range<'a, Bytes, (Bound<Bytes>, Bound<Bytes>), Bytes, Bytes>;
+
+/// An iterator over a range of `SkipMap`.
+pub struct MemTableIterator<'a> {
+    iter: SkipMapRangeIter<'a>,
+    item: (Bytes, Bytes),
+}
+
+impl<'a> MemTableIterator<'a> {
+    fn entry_to_item(entry: Option<Entry<'a, Bytes, Bytes>>) -> (Bytes, Bytes) {
+        entry
+            .map(|x| (x.key().clone(), x.value().clone()))
+            .unwrap_or_else(|| (Bytes::from_static(&[]), Bytes::from_static(&[])))
+    }
+
+    fn new(mut iter: SkipMapRangeIter<'a>) -> Self {
+        let entry = iter.next();
+
+        Self {
+            item: Self::entry_to_item(entry),
+            iter,
+        }
+    }
+}
+
+impl StorageIterator for MemTableIterator<'_> {
+    fn value(&self) -> &[u8] {
+        &self.item.1[..]
+    }
+
+    fn key(&self) -> &[u8] {
+        &self.item.0[..]
+    }
+
+    fn is_valid(&self) -> bool {
+        !self.item.0.is_empty()
+    }
+
+    fn next(&mut self) -> Result<()> {
+        let entry = self.iter.next();
+        self.item = Self::entry_to_item(entry);
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+#[path = "mem_table_test.rs"]
+mod tests;