From 76eaa8ac60747e011657b1e3dd52c1c1eb14076b Mon Sep 17 00:00:00 2001
From: PhotonQuantum <self@lightquantum.me>
Date: Fri, 15 Oct 2021 07:47:24 +0800
Subject: [PATCH] Add benchmark for stack read buffer

---
 benches/buffer.rs | 99 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 93 insertions(+), 6 deletions(-)

diff --git a/benches/buffer.rs b/benches/buffer.rs
index eaf4e53..cf4e4fa 100644
--- a/benches/buffer.rs
+++ b/benches/buffer.rs
@@ -1,19 +1,107 @@
 use std::io::{Cursor, Read};
+use std::io::Result as IoResult;
 
+use bytes::Buf;
 use criterion::*;
 use input_buffer::InputBuffer;
+
 use tungstenite::buffer::ReadBuffer;
 
 const CHUNK_SIZE: usize = 4096;
 
+/// A FIFO buffer for reading packets from the network.
+#[derive(Debug)]
+pub struct StackReadBuffer<const CHUNK_SIZE: usize> {
+    storage: Cursor<Vec<u8>>,
+    chunk: [u8; CHUNK_SIZE],
+}
+
+impl<const CHUNK_SIZE: usize> StackReadBuffer<CHUNK_SIZE> {
+    /// Create a new empty input buffer.
+    pub fn new() -> Self {
+        Self::with_capacity(CHUNK_SIZE)
+    }
+
+    /// Create a new empty input buffer with a given `capacity`.
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self::from_partially_read(Vec::with_capacity(capacity))
+    }
+
+    /// Create a input buffer filled with previously read data.
+    pub fn from_partially_read(part: Vec<u8>) -> Self {
+        Self { storage: Cursor::new(part), chunk: [0; CHUNK_SIZE] }
+    }
+
+    /// Get a cursor to the data storage.
+    pub fn as_cursor(&self) -> &Cursor<Vec<u8>> {
+        &self.storage
+    }
+
+    /// Get a cursor to the mutable data storage.
+    pub fn as_cursor_mut(&mut self) -> &mut Cursor<Vec<u8>> {
+        &mut self.storage
+    }
+
+    /// Consume the `ReadBuffer` and get the internal storage.
+    pub fn into_vec(mut self) -> Vec<u8> {
+        // Current implementation of `tungstenite-rs` expects that the `into_vec()` drains
+        // the data from the container that has already been read by the cursor.
+        self.clean_up();
+
+        // Now we can safely return the internal container.
+        self.storage.into_inner()
+    }
+
+    /// Read next portion of data from the given input stream.
+    pub fn read_from<S: Read>(&mut self, stream: &mut S) -> IoResult<usize> {
+        self.clean_up();
+        let size = stream.read(&mut self.chunk)?;
+        self.storage.get_mut().extend_from_slice(&self.chunk[..size]);
+        Ok(size)
+    }
+
+    /// Cleans ups the part of the vector that has been already read by the cursor.
+    fn clean_up(&mut self) {
+        let pos = self.storage.position() as usize;
+        self.storage.get_mut().drain(0..pos).count();
+        self.storage.set_position(0);
+    }
+}
+
+impl<const CHUNK_SIZE: usize> Buf for StackReadBuffer<CHUNK_SIZE> {
+    fn remaining(&self) -> usize {
+        Buf::remaining(self.as_cursor())
+    }
+
+    fn chunk(&self) -> &[u8] {
+        Buf::chunk(self.as_cursor())
+    }
+
+    fn advance(&mut self, cnt: usize) {
+        Buf::advance(self.as_cursor_mut(), cnt)
+    }
+}
+
+impl<const CHUNK_SIZE: usize> Default for StackReadBuffer<CHUNK_SIZE> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 #[inline]
-fn current_input_buffer(mut stream: impl Read) {
+fn input_buffer(mut stream: impl Read) {
     let mut buffer = InputBuffer::with_capacity(CHUNK_SIZE);
     while buffer.read_from(&mut stream).unwrap() != 0 {}
 }
 
 #[inline]
-fn fast_input_buffer(mut stream: impl Read) {
+fn stack_read_buffer(mut stream: impl Read) {
+    let mut buffer = StackReadBuffer::<CHUNK_SIZE>::new();
+    while buffer.read_from(&mut stream).unwrap() != 0 {}
+}
+
+#[inline]
+fn heap_read_buffer(mut stream: impl Read) {
     let mut buffer = ReadBuffer::<CHUNK_SIZE>::new();
     while buffer.read_from(&mut stream).unwrap() != 0 {}
 }
@@ -25,10 +113,9 @@ fn benchmark(c: &mut Criterion) {
 
     let mut group = c.benchmark_group("buffers");
     group.throughput(Throughput::Bytes(STREAM_SIZE as u64));
-    group.bench_function("InputBuffer", |b| {
-        b.iter(|| current_input_buffer(black_box(stream.clone())))
-    });
-    group.bench_function("ReadBuffer", |b| b.iter(|| fast_input_buffer(black_box(stream.clone()))));
+    group.bench_function("InputBuffer", |b| b.iter(|| input_buffer(black_box(stream.clone()))));
+    group.bench_function("ReadBuffer (stack)", |b| b.iter(|| stack_read_buffer(black_box(stream.clone()))));
+    group.bench_function("ReadBuffer (heap)", |b| b.iter(|| heap_read_buffer(black_box(stream.clone()))));
     group.finish();
 }