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#![forbid(unsafe_code, missing_docs)]
#![cfg_attr(test, deny(warnings))]
#![doc(test(attr(deny(warnings))))]
//! # Continuously read and write to memory using random offsets and lengths
//! [RandomAccessMemory] is a complete implementation of [random-access-storage](https://docs.rs/random-access-storage)
//! for in-memory storage.
//!
//! See also [random-access-disk](https://docs.rs/random-access-disk) for on-disk storage
//! that can be swapped with this.
//!
//! ## Examples
//!
//! Reading, writing, deleting and truncating:
//!
//! ```
//! # async_std::task::block_on(async {
//! use random_access_storage::RandomAccess;
//! use random_access_memory::RandomAccessMemory;
//!
//! let mut storage = RandomAccessMemory::default();
//! storage.write(0, b"hello").await.unwrap();
//! storage.write(5, b" world").await.unwrap();
//! assert_eq!(storage.read(0, 11).await.unwrap(), b"hello world");
//! assert_eq!(storage.len().await.unwrap(), 11);
//! storage.del(5, 2).await.unwrap();
//! assert_eq!(storage.read(5, 2).await.unwrap(), [0, 0]);
//! assert_eq!(storage.len().await.unwrap(), 11);
//! storage.truncate(2).await.unwrap();
//! assert_eq!(storage.len().await.unwrap(), 2);
//! storage.truncate(5).await.unwrap();
//! assert_eq!(storage.len().await.unwrap(), 5);
//! assert_eq!(storage.read(0, 5).await.unwrap(), [b'h', b'e', 0, 0, 0]);
//! # })
//! ```
//!
//! In order to get benefits from the swappable interface, you will
//! in most cases want to use generic functions for storage manipulation:
//!
//! ```
//! # async_std::task::block_on(async {
//! use random_access_storage::RandomAccess;
//! use random_access_memory::RandomAccessMemory;
//! use std::fmt::Debug;
//!
//! let mut storage = RandomAccessMemory::default();
//! write_hello_world(&mut storage).await;
//! assert_eq!(read_hello_world(&mut storage).await, b"hello world");
//!
//! /// Write with swappable storage
//! async fn write_hello_world<T>(storage: &mut T)
//! where T: RandomAccess + Debug + Send,
//! {
//! storage.write(0, b"hello").await.unwrap();
//! storage.write(5, b" world").await.unwrap();
//! }
//!
//! /// Read with swappable storage
//! async fn read_hello_world<T>(storage: &mut T) -> Vec<u8>
//! where T: RandomAccess + Debug + Send,
//! {
//! storage.read(0, 11).await.unwrap()
//! }
//! # })
//! ```
pub use intmap::IntMap;
use random_access_storage::{RandomAccess, RandomAccessError};
use std::cmp;
/// In-memory storage for random access
#[derive(Debug)]
pub struct RandomAccessMemory {
/// Length of each buffer
page_size: usize,
/// Allocated memory
buffers: IntMap<Vec<u8>>,
/// Total length of the data
length: u64,
}
impl Default for RandomAccessMemory {
/// Create a new instance with a 1mb page size.
fn default() -> Self {
RandomAccessMemory::new(1024 * 1024)
}
}
#[allow(clippy::needless_range_loop)]
impl RandomAccessMemory {
/// Create a new instance with `page_size` in bytes.
pub fn new(page_size: usize) -> Self {
RandomAccessMemory::with_buffers(page_size, IntMap::new())
}
/// Create a new instance with `page_size` in bytes, but pass the initial buffers to the constructor.
pub fn with_buffers(page_size: usize, buffers: IntMap<Vec<u8>>) -> Self {
RandomAccessMemory {
page_size,
buffers,
length: 0,
}
}
/// Returns the page number and index within that page for a given offset.
/// If `exclusive_end` is true, when hitting the exact border of two pages
/// gives the previous page and page size as index.
fn page_num_and_index(
&self,
offset: u64,
exclusive_end: bool,
) -> (usize, usize) {
let page_num = (offset / (self.page_size as u64)) as usize;
let page_index = (offset % (self.page_size as u64)) as usize;
if page_index == 0 && exclusive_end {
(if page_num > 0 { page_num - 1 } else { 0 }, self.page_size)
} else {
(page_num, page_index)
}
}
/// Zero given range
fn zero(&mut self, offset: u64, length: u64) {
let (first_page_num, first_page_start) =
self.page_num_and_index(offset, false);
let (last_page_num, last_page_end) =
self.page_num_and_index(offset + length, true);
// Check if we need to zero bytes in the first page
if first_page_start > 0
|| (first_page_num == last_page_num && last_page_end > 0)
{
if let Some(page) = self.buffers.get_mut(first_page_num as u64) {
// Need to zero part of the first page
let begin_page_end = first_page_start
+ cmp::min(length as usize, self.page_size - first_page_start);
for index in first_page_start..begin_page_end {
page[index] = 0;
}
}
}
// Delete intermediate pages
if last_page_num > first_page_num + 1
|| (first_page_start == 0 && last_page_num == first_page_num + 1)
{
let first_page_to_drop = if first_page_start == 0 {
first_page_num
} else {
first_page_num + 1
};
for index in first_page_to_drop..last_page_num {
self.buffers.remove(index as u64);
}
}
// Finally zero the last page
if last_page_num > first_page_num && last_page_end > 0 {
if let Some(page) = self.buffers.get_mut(last_page_num as u64) {
// Need to zero part of the final page
for index in 0..last_page_end {
page[index] = 0;
}
}
}
}
}
#[async_trait::async_trait]
impl RandomAccess for RandomAccessMemory {
async fn write(
&mut self,
offset: u64,
data: &[u8],
) -> Result<(), RandomAccessError> {
let new_len = offset + data.len() as u64;
if new_len > self.length {
self.length = new_len;
}
let mut page_num = (offset / self.page_size as u64) as usize;
let mut page_cursor =
(offset - (page_num * self.page_size) as u64) as usize;
let mut data_cursor = 0;
// Iterate over data, write to buffers. Subslice if the data is bigger than
// what we can write in a single go.
while data_cursor < data.len() {
let data_bound = data.len() - data_cursor;
let upper_bound = cmp::min(self.page_size, page_cursor + data_bound);
let range = page_cursor..upper_bound;
let range_len = (page_cursor..upper_bound).len();
// Allocate buffer if needed. Either append a new buffer to the end, or
// set a buffer in the center.
if self.buffers.get(page_num as u64).is_none() {
let buf = vec![0; self.page_size];
self.buffers.insert(page_num as u64, buf);
}
// Copy data from the vec slice.
// TODO: use a batch operation such as `.copy_from_slice()` so it can be
// optimized.
let buffer = &mut self.buffers.get_mut(page_num as u64).unwrap();
for (index, buf_index) in range.enumerate() {
buffer[buf_index] = data[data_cursor + index];
}
page_num += 1;
page_cursor = 0;
data_cursor += range_len;
}
Ok(())
}
async fn sync_all(&mut self) -> Result<(), RandomAccessError> {
Ok(())
}
async fn read(
&mut self,
offset: u64,
length: u64,
) -> Result<Vec<u8>, RandomAccessError> {
if (offset + length) > self.length {
return Err(RandomAccessError::OutOfBounds {
offset,
end: Some(offset + length),
length: self.length,
});
};
let mut page_num = (offset / self.page_size as u64) as usize;
let mut page_cursor =
(offset - (page_num * self.page_size) as u64) as usize;
let mut res_buf = vec![0; length as usize];
let mut res_cursor = 0; // Keep track we read the right amount of bytes.
let res_capacity = length;
while res_cursor < res_capacity {
let res_bound = res_capacity - res_cursor;
let page_bound = self.page_size - page_cursor;
let relative_bound = cmp::min(res_bound, page_bound as u64);
let upper_bound = page_cursor + relative_bound as usize;
let range = page_cursor..upper_bound;
// Fill until either we're done reading the page, or we're done
// filling the buffer. Whichever arrives sooner.
match self.buffers.get(page_num as u64) {
Some(buf) => {
for (index, buf_index) in range.enumerate() {
res_buf[res_cursor as usize + index] = buf[buf_index];
}
}
None => {
for (index, _) in range.enumerate() {
res_buf[res_cursor as usize + index] = 0;
}
}
}
res_cursor += relative_bound;
page_num += 1;
page_cursor = 0;
}
Ok(res_buf)
}
async fn del(
&mut self,
offset: u64,
length: u64,
) -> Result<(), RandomAccessError> {
if offset > self.length {
return Err(RandomAccessError::OutOfBounds {
offset,
end: None,
length: self.length,
});
};
if length == 0 {
// No-op
return Ok(());
}
// Delete is truncate if up to the current length or more is deleted
if offset + length >= self.length {
return self.truncate(offset).await;
}
// Deleting means zeroing
self.zero(offset, length);
Ok(())
}
#[allow(clippy::comparison_chain)]
async fn truncate(&mut self, length: u64) -> Result<(), RandomAccessError> {
let (current_last_page_num, _) = self.page_num_and_index(self.length, true);
if self.length < length {
let truncate_page_num = (length / self.page_size as u64) as usize;
// Remove all of the pages between the old length and this newer
// length that might have been left behind.
for index in current_last_page_num + 1..truncate_page_num + 1 {
self.buffers.remove(index as u64);
}
} else if self.length > length {
let delete_length =
((current_last_page_num + 1) * self.page_size) - length as usize;
// Make sure to zero the remainder to not leave anything but
// zeros lying around.
self.zero(length, delete_length as u64);
}
// Set new length
self.length = length;
Ok(())
}
async fn len(&mut self) -> Result<u64, RandomAccessError> {
Ok(self.length)
}
async fn is_empty(&mut self) -> Result<bool, RandomAccessError> {
Ok(self.length == 0)
}
}