feat(s2n-quic-core): add buffer::Deque implemention (#2207)

quic/s2n-quic-core/src/buffer.rs

@@ -1,12 +1,14 @@
 // Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
 
+pub mod deque;
 pub mod duplex;
 mod error;
 pub mod reader;
 pub mod reassembler;
 pub mod writer;
 
+pub use deque::Deque;
 pub use duplex::Duplex;
 pub use error::Error;
 pub use reader::Reader;

quic/s2n-quic-core/src/buffer/deque.rs

@@ -0,0 +1,237 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::slice::deque;
+use alloc::{boxed::Box, vec::Vec};
+use core::{fmt, mem::MaybeUninit};
+
+mod storage;
+
+#[cfg(test)]
+mod tests;
+
+/// A fixed-capacity ring buffer for bytes
+#[derive(Clone)]
+pub struct Deque {
+    bytes: Box<[MaybeUninit<u8>]>,
+    head: usize,
+    len: usize,
+}
+
+impl fmt::Debug for Deque {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Deque")
+            .field("len", &self.len())
+            .field("capacity", &self.capacity())
+            .finish()
+    }
+}
+
+impl From<Vec<u8>> for Deque {
+    #[inline]
+    fn from(mut buffer: Vec<u8>) -> Deque {
+        let len = buffer.len();
+        let mut capacity = buffer.capacity();
+        if !capacity.is_power_of_two() {
+            capacity = capacity.next_power_of_two();
+            buffer.reserve_exact(capacity - len);
+            debug_assert!(capacity.is_power_of_two());
+        }
+
+        unsafe {
+            buffer.set_len(capacity);
+        }
+
+        let bytes = buffer.into_boxed_slice();
+        let ptr = Box::into_raw(bytes);
+        let bytes = unsafe { Box::from_raw(ptr as *mut [MaybeUninit<u8>]) };
+
+        Self {
+            bytes,
+            head: 0,
+            len,
+        }
+    }
+}
+
+impl Deque {
+    #[inline]
+    pub fn new(mut capacity: usize) -> Self {
+        // Make sure capacity is set to a power of two
+        // https://doc.rust-lang.org/std/primitive.usize.html#method.next_power_of_two
+        //> Returns the smallest power of two greater than or equal to self.
+        capacity = capacity.next_power_of_two();
+
+        let mut bytes = Vec::<MaybeUninit<u8>>::with_capacity(capacity);
+        unsafe {
+            bytes.set_len(capacity);
+        }
+        let bytes = bytes.into_boxed_slice();
+
+        Self {
+            bytes,
+            head: 0,
+            len: 0,
+        }
+    }
+
+    #[inline]
+    pub fn capacity(&self) -> usize {
+        self.bytes.len()
+    }
+
+    #[inline]
+    pub fn remaining_capacity(&self) -> usize {
+        self.preconditions();
+        self.capacity() - self.len()
+    }
+
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len == 0
+    }
+
+    /// Resets the filled bytes in the buffer
+    ///
+    /// Note that data is not actually wiped with this method. If that behavior is desired then
+    /// calling [`Self::consume_filled`] should be preferred.
+    #[inline]
+    pub fn clear(&mut self) {
+        self.head = 0;
+        self.len = 0;
+    }
+
+    /// Consumes `len` bytes from the head of the buffer
+    ///
+    /// # Panics
+    ///
+    /// `len` MUST be less than or equal to [`Self::len`]
+    #[inline]
+    pub fn consume(&mut self, len: usize) {
+        self.preconditions();
+
+        assert!(self.len() >= len);
+
+        if len >= self.len() {
+            self.clear();
+            return;
+        }
+
+        // Wrap the head around the capacity
+        self.head = deque::wrap(&self.bytes, self.head, len);
+        self.len -= len;
+
+        self.postconditions()
+    }
+
+    /// Returns the filled bytes in the buffer
+    #[inline]
+    pub fn filled(&mut self) -> deque::Pair<&mut [u8]> {
+        self.preconditions();
+
+        unsafe {
+            // SAFETY: cursors guarantee memory is filled
+            deque::filled(&mut self.bytes, self.head, self.len).assume_init_mut()
+        }
+    }
+
+    /// Returns and consumes `len` filled bytes in the buffer
+    ///
+    /// # Panics
+    ///
+    /// `len` MUST be less than or equal to [`Self::len`]
+    #[inline]
+    pub fn consume_filled(&mut self, len: usize) -> deque::Pair<&mut [u8]> {
+        self.preconditions();
+
+        let head = self.head;
+
+        self.consume(len);
+
+        self.postconditions();
+
+        unsafe {
+            // SAFETY: cursors guarantee memory is filled
+            deque::filled(&mut self.bytes, head, len).assume_init_mut()
+        }
+    }
+
+    /// Returns the unfilled bytes in the buffer
+    ///
+    /// Callers will need to call [`Self::fill`] to indicate any writes that occurred to returned
+    /// slices.
+    #[inline]
+    pub fn unfilled(&mut self) -> deque::Pair<&mut [MaybeUninit<u8>]> {
+        self.preconditions();
+        deque::unfilled(&mut self.bytes, self.head, self.len)
+    }
+
+    /// Makes the buffer contiguous and contained in a single slice
+    #[inline]
+    pub fn make_contiguous(&mut self) -> &mut [u8] {
+        self.preconditions();
+        deque::make_contiguous(&mut self.bytes, &mut self.head, self.len);
+        self.postconditions();
+
+        let (head, tail) = self.filled().into();
+        debug_assert!(tail.is_empty());
+        head
+    }
+
+    /// Notifies the buffer that `len` bytes were written to it
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure the filled bytes were actually initialized
+    #[inline]
+    pub unsafe fn fill(&mut self, len: usize) -> Result<(), FillError> {
+        ensure!(self.remaining_capacity() >= len, Err(FillError(())));
+
+        self.len += len;
+
+        self.postconditions();
+
+        Ok(())
+    }
+
+    #[inline(always)]
+    fn preconditions(&self) {
+        unsafe {
+            assume!(deque::invariants(&self.bytes, self.head, self.len));
+            assume!(self.capacity().is_power_of_two());
+        }
+    }
+
+    #[inline(always)]
+    fn postconditions(&self) {
+        debug_assert!(deque::invariants(&self.bytes, self.head, self.len));
+    }
+}
+
+#[derive(Clone, Copy, Debug, Default)]
+pub struct FillError(());
+
+impl fmt::Display for FillError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "the buffer does not have enough capacity for the provided fill amount"
+        )
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for FillError {}
+
+#[cfg(feature = "std")]
+impl From<FillError> for std::io::Error {
+    #[inline]
+    fn from(value: FillError) -> Self {
+        Self::new(std::io::ErrorKind::InvalidInput, value)
+    }
+}