compression: avoid copy on none algo

This commit fixes the redundant copy that was done when calling `decompress`
with the `None` compression. We should see less memcpys now.

betree/src/compression/mod.rs

@@ -76,7 +76,7 @@ pub trait CompressionState: Write {
 }
 
 pub trait DecompressionState {
-    fn decompress(&mut self, data: &[u8]) -> Result<Box<[u8]>>;
+    fn decompress(&mut self, data: Buf) -> Result<Buf>;
 }
 
 mod none;

betree/src/compression/none.rs

@@ -62,8 +62,8 @@ impl CompressionState for NoneCompression {
 }
 
 impl DecompressionState for NoneDecompression {
-    fn decompress(&mut self, data: &[u8]) -> Result<Box<[u8]>> {
+    fn decompress(&mut self, data: Buf) -> Result<Buf> {
         // FIXME: pass-through Buf, reusing alloc
-        Ok(data.to_vec().into_boxed_slice())
+        Ok(data)
     }
 }

betree/src/compression/zstd.rs

@@ -122,8 +122,8 @@ impl CompressionState for ZstdCompression {
 }
 
 impl DecompressionState for ZstdDecompression {
-    fn decompress(&mut self, data: &[u8]) -> Result<Box<[u8]>> {
-        let size = u32::read_from_buffer(data).unwrap();
+    fn decompress(&mut self, data: Buf) -> Result<Buf> {
+        let size = u32::read_from_buffer(data.as_ref()).unwrap();
         let mut buf = BufWrite::with_capacity(Block::round_up_from_bytes(size));
 
         let mut input = zstd::stream::raw::InBuffer::around(&data[DATA_OFF..]);
@@ -150,7 +150,7 @@ impl DecompressionState for ZstdDecompression {
         while self.writer.flush(&mut output)? > 0 {}
         self.writer.finish(&mut output, finished_frame)?;
 
-        Ok(buf.into_buf().as_ref().into())
+        Ok(buf.into_buf())
     }
 }
 
@@ -170,7 +170,7 @@ mod tests {
         let mut comp = zstd.new_compression().unwrap();
         let c_buf = comp.finish(buf.clone()).unwrap();
         let mut decomp = zstd.decompression_tag().new_decompression().unwrap();
-        let d_buf = decomp.decompress(c_buf.as_ref()).unwrap();
+        let d_buf = decomp.decompress(c_buf).unwrap();
         assert_eq!(buf.as_ref().len(), d_buf.as_ref().len());
     }
 

betree/src/data_management/dmu.rs

@@ -231,8 +231,8 @@ where
             .read(op.size(), op.offset(), op.checksum().clone())?;
 
         let object: Node<ObjRef<ObjectPointer<SPL::Checksum>>> = {
-            let data = decompression_state.decompress(&compressed_data)?;
-            Object::unpack_at(op.offset(), op.info(), data)?
+            let data = decompression_state.decompress(compressed_data)?;
+            Object::unpack_at(op.offset(), op.info(), data.into_boxed_slice())?
         };
         let key = ObjectKey::Unmodified { offset, generation };
         self.insert_object_into_cache(key, TaggedCacheValue::new(RwLock::new(object), pivot_key));
@@ -413,7 +413,6 @@ where
             state.finish()
         };
 
-        // FIXME: COMPRESSION
         self.pool.begin_write(compressed_data, offset)?;
 
         let obj_ptr = ObjectPointer {
@@ -937,8 +936,8 @@ where
             let data = ptr
                 .decompression_tag()
                 .new_decompression()?
-                .decompress(&compressed_data)?;
-            Object::unpack_at(ptr.offset(), ptr.info(), data)?
+                .decompress(compressed_data)?;
+            Object::unpack_at(ptr.offset(), ptr.info(), data.into_boxed_slice())?
         };
         let key = ObjectKey::Unmodified {
             offset: ptr.offset(),