update assets Reader to use AsyncSeekForward rather than AsyncSeek

Author: ldubos

crates/bevy_asset/src/io/file/file_asset.rs

@@ -1,14 +1,35 @@
 use crate::io::{
-    get_meta_path, AssetReader, AssetReaderError, AssetWriter, AssetWriterError, PathStream,
-    Reader, Writer,
+    get_meta_path, AssetReader, AssetReaderError, AssetWriter, AssetWriterError, AsyncSeekForward,
+    PathStream, Reader, Writer,
 };
 use async_fs::{read_dir, File};
+use futures_io::AsyncSeek;
 use futures_lite::StreamExt;
 
+use core::{pin::Pin, task, task::Poll};
 use std::path::Path;
 
 use super::{FileAssetReader, FileAssetWriter};
 
+impl AsyncSeekForward for File {
+    fn poll_seek_forward(
+        mut self: Pin<&mut Self>,
+        cx: &mut task::Context<'_>,
+        offset: u64,
+    ) -> Poll<futures_io::Result<u64>> {
+        let offset: Result<i64, _> = offset.try_into();
+
+        if let Ok(offset) = offset {
+            Pin::new(&mut self).poll_seek(cx, futures_io::SeekFrom::Current(offset))
+        } else {
+            Poll::Ready(Err(std::io::Error::new(
+                std::io::ErrorKind::InvalidInput,
+                "seek position is out of range",
+            )))
+        }
+    }
+}
+
 impl Reader for File {}
 
 impl AssetReader for FileAssetReader {

crates/bevy_asset/src/io/file/sync_file_asset.rs

@@ -1,9 +1,9 @@
-use futures_io::{AsyncRead, AsyncSeek, AsyncWrite};
+use futures_io::{AsyncRead, AsyncWrite};
 use futures_lite::Stream;
 
 use crate::io::{
-    get_meta_path, AssetReader, AssetReaderError, AssetWriter, AssetWriterError, PathStream,
-    Reader, Writer,
+    get_meta_path, AssetReader, AssetReaderError, AssetWriter, AssetWriterError, AsyncSeekForward,
+    PathStream, Reader, Writer,
 };
 
 use core::{pin::Pin, task::Poll};
@@ -29,14 +29,16 @@ impl AsyncRead for FileReader {
     }
 }
 
-impl AsyncSeek for FileReader {
-    fn poll_seek(
+impl AsyncSeekForward for FileReader {
+    fn poll_seek_forward(
         self: Pin<&mut Self>,
         _cx: &mut core::task::Context<'_>,
-        pos: std::io::SeekFrom,
+        offset: u64,
     ) -> Poll<std::io::Result<u64>> {
         let this = self.get_mut();
-        let seek = this.0.seek(pos);
+        let current = this.0.stream_position()?;
+        let seek = this.0.seek(std::io::SeekFrom::Start(current + offset));
+
         Poll::Ready(seek)
     }
 }

crates/bevy_asset/src/io/memory.rs

@@ -2,13 +2,12 @@ use crate::io::{AssetReader, AssetReaderError, PathStream, Reader};
 use alloc::sync::Arc;
 use bevy_utils::HashMap;
 use core::{pin::Pin, task::Poll};
-use futures_io::{AsyncRead, AsyncSeek};
+use futures_io::AsyncRead;
 use futures_lite::{ready, Stream};
 use parking_lot::RwLock;
-use std::{
-    io::SeekFrom,
-    path::{Path, PathBuf},
-};
+use std::path::{Path, PathBuf};
+
+use super::AsyncSeekForward;
 
 #[derive(Default, Debug)]
 struct DirInternal {
@@ -247,37 +246,20 @@ impl AsyncRead for DataReader {
     }
 }
 
-impl AsyncSeek for DataReader {
-    fn poll_seek(
+impl AsyncSeekForward for DataReader {
+    fn poll_seek_forward(
         mut self: Pin<&mut Self>,
         _cx: &mut core::task::Context<'_>,
-        pos: SeekFrom,
+        offset: u64,
     ) -> Poll<std::io::Result<u64>> {
-        let result = match pos {
-            SeekFrom::Start(offset) => offset.try_into(),
-            SeekFrom::End(offset) => self
-                .data
-                .value()
-                .len()
-                .try_into()
-                .map(|len: i64| len - offset),
-            SeekFrom::Current(offset) => self
-                .bytes_read
-                .try_into()
-                .map(|bytes_read: i64| bytes_read + offset),
-        };
+        let result = self
+            .bytes_read
+            .try_into()
+            .map(|bytes_read: u64| bytes_read + offset);
 
         if let Ok(new_pos) = result {
-            if new_pos < 0 {
-                Poll::Ready(Err(std::io::Error::new(
-                    std::io::ErrorKind::InvalidInput,
-                    "seek position is out of range",
-                )))
-            } else {
-                self.bytes_read = new_pos as _;
-
-                Poll::Ready(Ok(new_pos as _))
-            }
+            self.bytes_read = new_pos as _;
+            Poll::Ready(Ok(new_pos as _))
         } else {
             Poll::Ready(Err(std::io::Error::new(
                 std::io::ErrorKind::InvalidInput,

crates/bevy_asset/src/io/mod.rs

@@ -28,12 +28,9 @@ use core::{
     pin::Pin,
     task::{Context, Poll},
 };
-use futures_io::{AsyncRead, AsyncSeek, AsyncWrite};
+use futures_io::{AsyncRead, AsyncWrite};
 use futures_lite::{ready, Stream};
-use std::{
-    io::SeekFrom,
-    path::{Path, PathBuf},
-};
+use std::path::{Path, PathBuf};
 use thiserror::Error;
 
 /// Errors that occur while loading assets.
@@ -83,13 +80,51 @@ pub const STACK_FUTURE_SIZE: usize = 10 * size_of::<&()>();
 
 pub use stackfuture::StackFuture;
 
+/// Asynchronously advances the cursor position by a specified number of bytes.
+///
+/// This trait is a simplified version of the [`futures_io::AsyncSeek`] trait, providing
+/// support exclusively for the [`futures_io::SeekFrom::Current`] variant. It allows for relative
+/// seeking from the current cursor position.
+pub trait AsyncSeekForward {
+    /// Attempts to asynchronously seek forward by a specified number of bytes from the current cursor position.
+    ///
+    /// Seeking beyond the end of the stream is allowed and the behavior for this case is defined by the implementation.
+    /// The new position, relative to the beginning of the stream, should be returned upon successful completion
+    /// of the seek operation.
+    ///
+    /// If the seek operation completes successfully,
+    /// the new position relative to the beginning of the stream should be returned.
+    ///
+    /// # Implementation
+    ///
+    /// Implementations of this trait should handle [`Poll::Pending`] correctly, converting
+    /// [`std::io::ErrorKind::WouldBlock`] errors into [`Poll::Pending`] to indicate that the operation is not
+    /// yet complete and should be retried, and either internally retry or convert
+    /// [`std::io::ErrorKind::Interrupted`] into another error kind.
+    fn poll_seek_forward(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        offset: u64,
+    ) -> Poll<futures_io::Result<u64>>;
+}
+
+impl<T: ?Sized + AsyncSeekForward + Unpin> AsyncSeekForward for Box<T> {
+    fn poll_seek_forward(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        offset: u64,
+    ) -> Poll<futures_io::Result<u64>> {
+        Pin::new(&mut **self).poll_seek_forward(cx, offset)
+    }
+}
+
 /// A type returned from [`AssetReader::read`], which is used to read the contents of a file
 /// (or virtual file) corresponding to an asset.
 ///
-/// This is essentially a trait alias for types implementing  [`AsyncRead`] and [`AsyncSeek`].
+/// This is essentially a trait alias for types implementing [`AsyncRead`] and [`AsyncSeekForward`].
 /// The only reason a blanket implementation is not provided for applicable types is to allow
 /// implementors to override the provided implementation of [`Reader::read_to_end`].
-pub trait Reader: AsyncRead + AsyncSeek + Unpin + Send + Sync {
+pub trait Reader: AsyncRead + AsyncSeekForward + Unpin + Send + Sync {
     /// Reads the entire contents of this reader and appends them to a vec.
     ///
     /// # Note for implementors
@@ -559,32 +594,20 @@ impl AsyncRead for VecReader {
     }
 }
 
-impl AsyncSeek for VecReader {
-    fn poll_seek(
+impl AsyncSeekForward for VecReader {
+    fn poll_seek_forward(
         mut self: Pin<&mut Self>,
         _cx: &mut Context<'_>,
-        pos: SeekFrom,
+        offset: u64,
     ) -> Poll<std::io::Result<u64>> {
-        let result = match pos {
-            SeekFrom::Start(offset) => offset.try_into(),
-            SeekFrom::End(offset) => self.bytes.len().try_into().map(|len: i64| len - offset),
-            SeekFrom::Current(offset) => self
-                .bytes_read
-                .try_into()
-                .map(|bytes_read: i64| bytes_read + offset),
-        };
+        let result = self
+            .bytes_read
+            .try_into()
+            .map(|bytes_read: u64| bytes_read + offset);
 
         if let Ok(new_pos) = result {
-            if new_pos < 0 {
-                Poll::Ready(Err(std::io::Error::new(
-                    std::io::ErrorKind::InvalidInput,
-                    "seek position is out of range",
-                )))
-            } else {
-                self.bytes_read = new_pos as _;
-
-                Poll::Ready(Ok(new_pos as _))
-            }
+            self.bytes_read = new_pos as _;
+            Poll::Ready(Ok(new_pos as _))
         } else {
             Poll::Ready(Err(std::io::Error::new(
                 std::io::ErrorKind::InvalidInput,
@@ -644,32 +667,21 @@ impl<'a> AsyncRead for SliceReader<'a> {
     }
 }
 
-impl<'a> AsyncSeek for SliceReader<'a> {
-    fn poll_seek(
+impl<'a> AsyncSeekForward for SliceReader<'a> {
+    fn poll_seek_forward(
         mut self: Pin<&mut Self>,
         _cx: &mut Context<'_>,
-        pos: SeekFrom,
+        offset: u64,
     ) -> Poll<std::io::Result<u64>> {
-        let result = match pos {
-            SeekFrom::Start(offset) => offset.try_into(),
-            SeekFrom::End(offset) => self.bytes.len().try_into().map(|len: i64| len - offset),
-            SeekFrom::Current(offset) => self
-                .bytes_read
-                .try_into()
-                .map(|bytes_read: i64| bytes_read + offset),
-        };
+        let result = self
+            .bytes_read
+            .try_into()
+            .map(|bytes_read: u64| bytes_read + offset);
 
         if let Ok(new_pos) = result {
-            if new_pos < 0 {
-                Poll::Ready(Err(std::io::Error::new(
-                    std::io::ErrorKind::InvalidInput,
-                    "seek position is out of range",
-                )))
-            } else {
-                self.bytes_read = new_pos as _;
+            self.bytes_read = new_pos as _;
 
-                Poll::Ready(Ok(new_pos as _))
-            }
+            Poll::Ready(Ok(new_pos as _))
         } else {
             Poll::Ready(Err(std::io::Error::new(
                 std::io::ErrorKind::InvalidInput,

crates/bevy_asset/src/io/processor_gated.rs

@@ -7,15 +7,15 @@ use alloc::sync::Arc;
 use async_lock::RwLockReadGuardArc;
 use bevy_utils::tracing::trace;
 use core::{pin::Pin, task::Poll};
-use futures_io::{AsyncRead, AsyncSeek};
-use std::{io::SeekFrom, path::Path};
+use futures_io::AsyncRead;
+use std::path::Path;
 
-use super::ErasedAssetReader;
+use super::{AsyncSeekForward, ErasedAssetReader};
 
 /// An [`AssetReader`] that will prevent asset (and asset metadata) read futures from returning for a
 /// given path until that path has been processed by [`AssetProcessor`].
 ///
-/// [`AssetProcessor`]: crate::processor::AssetProcessor   
+/// [`AssetProcessor`]: crate::processor::AssetProcessor
 pub struct ProcessorGatedReader {
     reader: Box<dyn ErasedAssetReader>,
     source: AssetSourceId<'static>,
@@ -142,13 +142,13 @@ impl AsyncRead for TransactionLockedReader<'_> {
     }
 }
 
-impl AsyncSeek for TransactionLockedReader<'_> {
-    fn poll_seek(
+impl AsyncSeekForward for TransactionLockedReader<'_> {
+    fn poll_seek_forward(
         mut self: Pin<&mut Self>,
         cx: &mut core::task::Context<'_>,
-        pos: SeekFrom,
+        offset: u64,
     ) -> Poll<std::io::Result<u64>> {
-        Pin::new(&mut self.reader).poll_seek(cx, pos)
+        Pin::new(&mut self.reader).poll_seek_forward(cx, offset)
     }
 }