From 53cda6d85ade41080b294881be043060cbe2f1da Mon Sep 17 00:00:00 2001
From: Christopher Hotchkiss <christopher.hotchkiss@gmail.com>
Date: Sun, 12 Sep 2021 10:21:14 -0400
Subject: [PATCH] Changed to use supplied buffers to reduce allocations

---
 src/engine/io/page_formats/page_offset.rs | 26 +++++++++++++++-
 src/engine/io/row_formats/item_pointer.rs | 38 +++++++++--------------
 src/engine/io/row_formats/row_data.rs     |  3 +-
 3 files changed, 40 insertions(+), 27 deletions(-)

diff --git a/src/engine/io/page_formats/page_offset.rs b/src/engine/io/page_formats/page_offset.rs
index ffe6efb..13a4939 100644
--- a/src/engine/io/page_formats/page_offset.rs
+++ b/src/engine/io/page_formats/page_offset.rs
@@ -2,7 +2,9 @@ use crate::{
     constants::{PAGES_PER_FILE, PAGE_SIZE},
     engine::io::ConstEncodedSize,
 };
+use bytes::{Buf, BufMut};
 use std::{
+    convert::TryFrom,
     fmt,
     mem::size_of,
     num::TryFromIntError,
@@ -14,6 +16,26 @@ use thiserror::Error;
 pub struct PageOffset(pub usize);
 
 impl PageOffset {
+    pub fn serialize(&self, buffer: &mut impl BufMut) {
+        //TODO switch this and other serialize calls to usize based once my pull request is accepted
+        //https://github.com/tokio-rs/bytes/pull/511
+        buffer.put_uint_le(self.0 as u64, size_of::<usize>());
+    }
+
+    pub fn parse(buffer: &mut impl Buf) -> Result<Self, PageOffsetError> {
+        if buffer.remaining() < size_of::<usize>() {
+            return Err(PageOffsetError::BufferTooShort(
+                size_of::<usize>(),
+                buffer.remaining(),
+            ));
+        }
+
+        let value = buffer.get_uint_le(size_of::<usize>());
+        let page = usize::try_from(value)?;
+
+        Ok(PageOffset(page))
+    }
+
     /// This will calculate a page offset based on the max file count and the offset from the first
     /// non-zero page in a file.
     ///
@@ -101,8 +123,10 @@ impl Mul for PageOffset {
     }
 }
 
-#[derive(Debug, Error)]
+#[derive(Debug, Error, PartialEq)]
 pub enum PageOffsetError {
+    #[error("Not enough space to parse usize need {0} got {1}")]
+    BufferTooShort(usize, usize),
     #[error(transparent)]
     TryFromIntError(#[from] TryFromIntError),
 }
diff --git a/src/engine/io/row_formats/item_pointer.rs b/src/engine/io/row_formats/item_pointer.rs
index 07f8364..77141e5 100644
--- a/src/engine/io/row_formats/item_pointer.rs
+++ b/src/engine/io/row_formats/item_pointer.rs
@@ -3,7 +3,7 @@
 //!
 //! We will be treating this a little different since our size will be based on usize
 
-use crate::engine::io::page_formats::PageOffset;
+use crate::engine::io::page_formats::{PageOffset, PageOffsetError};
 use crate::engine::io::ConstEncodedSize;
 
 use super::super::page_formats::{UInt12, UInt12Error};
@@ -25,28 +25,15 @@ impl ItemPointer {
         ItemPointer { page, count }
     }
 
-    pub fn serialize(&self) -> Bytes {
-        let mut buffer = BytesMut::with_capacity(size_of::<ItemPointer>());
-
-        buffer.put_slice(&self.page.0.to_le_bytes());
-        UInt12::serialize_packed(&mut buffer, &[self.count]);
-
-        buffer.freeze()
+    pub fn serialize(&self, buffer: &mut impl BufMut) {
+        self.page.serialize(buffer);
+        UInt12::serialize_packed(buffer, &[self.count]);
     }
 
     pub fn parse(buffer: &mut impl Buf) -> Result<Self, ItemPointerError> {
-        if buffer.remaining() < size_of::<usize>() {
-            return Err(ItemPointerError::BufferTooShort(
-                size_of::<usize>(),
-                buffer.remaining(),
-            ));
-        }
-
-        let value = buffer.get_uint_le(size_of::<usize>());
-        let page = usize::try_from(value)?;
-
+        let po = PageOffset::parse(buffer)?;
         let items = UInt12::parse_packed(buffer, 1)?;
-        Ok(ItemPointer::new(PageOffset(page), items[0]))
+        Ok(ItemPointer::new(po, items[0]))
     }
 }
 
@@ -66,8 +53,8 @@ impl ConstEncodedSize for ItemPointer {
 
 #[derive(Debug, Error, PartialEq)]
 pub enum ItemPointerError {
-    #[error("Not enough space to parse usize need {0} got {1}")]
-    BufferTooShort(usize, usize),
+    #[error(transparent)]
+    PageOffsetError(#[from] PageOffsetError),
     #[error(transparent)]
     TryFromIntError(#[from] TryFromIntError),
     #[error(transparent)]
@@ -84,8 +71,9 @@ mod tests {
     fn test_item_pointer_roundtrip() -> Result<(), Box<dyn std::error::Error>> {
         let test = ItemPointer::new(PageOffset(1), UInt12::new(1).unwrap());
 
-        let mut test_serial = test.clone().serialize();
-        let test_reparse = ItemPointer::parse(&mut test_serial)?;
+        let mut buffer = BytesMut::new();
+        test.serialize(&mut buffer);
+        let test_reparse = ItemPointer::parse(&mut buffer.freeze())?;
 
         assert_eq!(test, test_reparse);
         Ok(())
@@ -96,7 +84,9 @@ mod tests {
         let parse = ItemPointer::parse(&mut Bytes::new());
 
         assert_eq!(
-            Err(ItemPointerError::BufferTooShort(size_of::<usize>(), 0)),
+            Err(ItemPointerError::PageOffsetError(
+                PageOffsetError::BufferTooShort(size_of::<usize>(), 0)
+            )),
             parse
         );
 
diff --git a/src/engine/io/row_formats/row_data.rs b/src/engine/io/row_formats/row_data.rs
index 4d8a7a4..da2a6d5 100644
--- a/src/engine/io/row_formats/row_data.rs
+++ b/src/engine/io/row_formats/row_data.rs
@@ -64,8 +64,7 @@ impl RowData {
     pub fn serialize(&self, buffer: &mut impl BufMut) {
         buffer.put_u64_le(self.min.get_u64());
         buffer.put_u64_le(self.max.unwrap_or_else(|| TransactionId::new(0)).get_u64());
-
-        buffer.put(self.item_pointer.serialize());
+        self.item_pointer.serialize(buffer);
 
         //If there is null we add it to the flags and write a nullmask
         let mut mask = InfoMask::empty();