| // Licensed to the Apache Software Foundation (ASF) under one |
| // or more contributor license agreements. See the NOTICE file |
| // distributed with this work for additional information |
| // regarding copyright ownership. The ASF licenses this file |
| // to you under the Apache License, Version 2.0 (the |
| // "License"); you may not use this file except in compliance |
| // with the License. You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, |
| // software distributed under the License is distributed on an |
| // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| // KIND, either express or implied. See the License for the |
| // specific language governing permissions and limitations |
| // under the License. |
| |
| use std::mem; |
| use std::ops::DerefMut; |
| |
| use bytes::Bytes; |
| use futures::Future; |
| |
| use crate::raw::*; |
| use crate::*; |
| |
| /// Reader is a type erased [`Read`]. |
| pub type Reader = Box<dyn ReadDyn>; |
| |
| /// Read is the internal trait used by OpenDAL to read data from storage. |
| /// |
| /// Users should not use or import this trait unless they are implementing an `Accessor`. |
| /// |
| /// # Notes |
| /// |
| /// ## Object Safety |
| /// |
| /// `Read` uses `async in trait`, making it not object safe, preventing the use of `Box<dyn Read>`. |
| /// To address this, we've introduced [`ReadDyn`] and its compatible type `Box<dyn ReadDyn>`. |
| /// |
| /// `ReadDyn` uses `Box::pin()` to transform the returned future into a [`BoxedFuture`], introducing |
| /// an additional layer of indirection and an extra allocation. Ideally, `ReadDyn` should occur only |
| /// once, at the outermost level of our API. |
| pub trait Read: Unpin + Send + Sync { |
| /// Read at the given offset with the given size. |
| fn read(&mut self) -> impl Future<Output = Result<Buffer>> + MaybeSend; |
| |
| /// Read all data from the reader. |
| fn read_all(&mut self) -> impl Future<Output = Result<Buffer>> + MaybeSend { |
| async { |
| let mut bufs = vec![]; |
| loop { |
| match self.read().await { |
| Ok(buf) if buf.is_empty() => break, |
| Ok(buf) => bufs.push(buf), |
| Err(err) => return Err(err), |
| } |
| } |
| Ok(bufs.into_iter().flatten().collect()) |
| } |
| } |
| } |
| |
| impl Read for () { |
| async fn read(&mut self) -> Result<Buffer> { |
| Err(Error::new( |
| ErrorKind::Unsupported, |
| "output reader doesn't support read", |
| )) |
| } |
| } |
| |
| impl Read for Bytes { |
| async fn read(&mut self) -> Result<Buffer> { |
| Ok(Buffer::from(self.split_off(0))) |
| } |
| } |
| |
| impl Read for Buffer { |
| async fn read(&mut self) -> Result<Buffer> { |
| Ok(mem::take(self)) |
| } |
| } |
| |
| /// ReadDyn is the dyn version of [`Read`] make it possible to use as |
| /// `Box<dyn ReadDyn>`. |
| pub trait ReadDyn: Unpin + Send + Sync { |
| /// The dyn version of [`Read::read`]. |
| /// |
| /// This function returns a boxed future to make it object safe. |
| fn read_dyn(&mut self) -> BoxedFuture<'_, Result<Buffer>>; |
| |
| /// The dyn version of [`Read::read_all`] |
| fn read_all_dyn(&mut self) -> BoxedFuture<'_, Result<Buffer>>; |
| } |
| |
| impl<T: Read + ?Sized> ReadDyn for T { |
| fn read_dyn(&mut self) -> BoxedFuture<'_, Result<Buffer>> { |
| Box::pin(self.read()) |
| } |
| |
| fn read_all_dyn(&mut self) -> BoxedFuture<'_, Result<Buffer>> { |
| Box::pin(self.read_all()) |
| } |
| } |
| |
| /// # NOTE |
| /// |
| /// Take care about the `deref_mut()` here. This makes sure that we are calling functions |
| /// upon `&mut T` instead of `&mut Box<T>`. The later could result in infinite recursion. |
| impl<T: ReadDyn + ?Sized> Read for Box<T> { |
| async fn read(&mut self) -> Result<Buffer> { |
| self.deref_mut().read_dyn().await |
| } |
| |
| async fn read_all(&mut self) -> Result<Buffer> { |
| self.deref_mut().read_all_dyn().await |
| } |
| } |