opendal/raw/oio/list/
page_list.rs

1// Licensed to the Apache Software Foundation (ASF) under one
2// or more contributor license agreements.  See the NOTICE file
3// distributed with this work for additional information
4// regarding copyright ownership.  The ASF licenses this file
5// to you under the Apache License, Version 2.0 (the
6// "License"); you may not use this file except in compliance
7// with the License.  You may obtain a copy of the License at
8//
9//   http://www.apache.org/licenses/LICENSE-2.0
10//
11// Unless required by applicable law or agreed to in writing,
12// software distributed under the License is distributed on an
13// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
14// KIND, either express or implied.  See the License for the
15// specific language governing permissions and limitations
16// under the License.
17
18use std::collections::VecDeque;
19use std::future::Future;
20
21use crate::raw::*;
22use crate::*;
23
24/// PageList is used to implement [`oio::List`] based on API supporting pagination. By implementing
25/// PageList, services don't need to care about the details of page list.
26///
27/// # Architecture
28///
29/// The architecture after adopting [`PageList`]:
30///
31/// - Services impl `PageList`
32/// - `PageLister` impl `List`
33/// - Expose `PageLister` as `Accessor::Lister`
34pub trait PageList: Send + Sync + Unpin + 'static {
35    /// next_page is used to fetch next page of entries from underlying storage.
36    #[cfg(not(target_arch = "wasm32"))]
37    fn next_page(&self, ctx: &mut PageContext) -> impl Future<Output = Result<()>> + MaybeSend;
38    #[cfg(target_arch = "wasm32")]
39    fn next_page(&self, ctx: &mut PageContext) -> impl Future<Output = Result<()>>;
40}
41
42/// PageContext is the context passing between `PageList`.
43///
44/// [`PageLister`] will init the PageContext, and implementer of [`PageList`] should fill the `PageContext`
45/// based on their needs.
46///
47/// - Set `done` to `true` if all page have been fetched.
48/// - Update `token` if there is more page to fetch. `token` is not exposed to users, it's internal used only.
49/// - Push back into the entries for each entry fetched from underlying storage.
50///
51/// NOTE: `entries` is a `VecDeque` to avoid unnecessary memory allocation. Only `push_back` is allowed.
52pub struct PageContext {
53    /// done is used to indicate whether the list operation is done.
54    pub done: bool,
55    /// token is used by underlying storage services to fetch next page.
56    pub token: String,
57    /// entries are used to store entries fetched from underlying storage.
58    ///
59    /// Please always reuse the same `VecDeque` to avoid unnecessary memory allocation.
60    /// PageLister makes sure that entries is reset before calling `next_page`. Implementer
61    /// can call `push_back` on `entries` directly.
62    pub entries: VecDeque<oio::Entry>,
63}
64
65/// PageLister implements [`oio::List`] based on [`PageList`].
66pub struct PageLister<L: PageList> {
67    inner: L,
68    ctx: PageContext,
69}
70
71impl<L> PageLister<L>
72where
73    L: PageList,
74{
75    /// Create a new PageLister.
76    pub fn new(l: L) -> Self {
77        Self {
78            inner: l,
79            ctx: PageContext {
80                done: false,
81                token: "".to_string(),
82                entries: VecDeque::new(),
83            },
84        }
85    }
86}
87
88impl<L> oio::List for PageLister<L>
89where
90    L: PageList,
91{
92    async fn next(&mut self) -> Result<Option<oio::Entry>> {
93        loop {
94            if let Some(entry) = self.ctx.entries.pop_front() {
95                return Ok(Some(entry));
96            }
97            if self.ctx.done {
98                return Ok(None);
99            }
100
101            self.inner.next_page(&mut self.ctx).await?;
102        }
103    }
104}
opendal/raw/oio/list/page_list.rs

opendal/raw/oio/list/
page_list.rs
