1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
|
use core::ops::Range;
use std::boxed::Box;
use std::cell::RefCell;
use std::collections::hash_map::Entry;
use std::collections::HashMap;
use std::convert::TryInto;
use std::io::{Read, Seek, SeekFrom};
use std::mem;
use std::vec::Vec;
use crate::read::ReadRef;
/// An implementation of `ReadRef` for data in a stream that implements
/// `Read + Seek`.
///
/// Contains a cache of read-only blocks of data, allowing references to
/// them to be returned. Entries in the cache are never removed.
/// Entries are keyed on the offset and size of the read.
/// Currently overlapping reads are considered separate reads.
#[derive(Debug)]
pub struct ReadCache<R: Read + Seek> {
cache: RefCell<ReadCacheInternal<R>>,
}
#[derive(Debug)]
struct ReadCacheInternal<R: Read + Seek> {
read: R,
bufs: HashMap<(u64, u64), Box<[u8]>>,
strings: HashMap<(u64, u8), Box<[u8]>>,
}
impl<R: Read + Seek> ReadCache<R> {
/// Create an empty `ReadCache` for the given stream.
pub fn new(read: R) -> Self {
ReadCache {
cache: RefCell::new(ReadCacheInternal {
read,
bufs: HashMap::new(),
strings: HashMap::new(),
}),
}
}
/// Return an implementation of `ReadRef` that restricts reads
/// to the given range of the stream.
pub fn range(&self, offset: u64, size: u64) -> ReadCacheRange<'_, R> {
ReadCacheRange {
r: self,
offset,
size,
}
}
/// Free buffers used by the cache.
pub fn clear(&mut self) {
self.cache.borrow_mut().bufs.clear();
}
/// Unwrap this `ReadCache<R>`, returning the underlying reader.
pub fn into_inner(self) -> R {
self.cache.into_inner().read
}
}
impl<'a, R: Read + Seek> ReadRef<'a> for &'a ReadCache<R> {
fn len(self) -> Result<u64, ()> {
let cache = &mut *self.cache.borrow_mut();
cache.read.seek(SeekFrom::End(0)).map_err(|_| ())
}
fn read_bytes_at(self, offset: u64, size: u64) -> Result<&'a [u8], ()> {
if size == 0 {
return Ok(&[]);
}
let cache = &mut *self.cache.borrow_mut();
let buf = match cache.bufs.entry((offset, size)) {
Entry::Occupied(entry) => entry.into_mut(),
Entry::Vacant(entry) => {
let size = size.try_into().map_err(|_| ())?;
cache
.read
.seek(SeekFrom::Start(offset as u64))
.map_err(|_| ())?;
let mut bytes = vec![0; size].into_boxed_slice();
cache.read.read_exact(&mut bytes).map_err(|_| ())?;
entry.insert(bytes)
}
};
// Extend the lifetime to that of self.
// This is OK because we never mutate or remove entries.
Ok(unsafe { mem::transmute::<&[u8], &[u8]>(buf) })
}
fn read_bytes_at_until(self, range: Range<u64>, delimiter: u8) -> Result<&'a [u8], ()> {
let cache = &mut *self.cache.borrow_mut();
let buf = match cache.strings.entry((range.start, delimiter)) {
Entry::Occupied(entry) => entry.into_mut(),
Entry::Vacant(entry) => {
cache
.read
.seek(SeekFrom::Start(range.start))
.map_err(|_| ())?;
let max_check: usize = (range.end - range.start).try_into().map_err(|_| ())?;
// Strings should be relatively small.
// TODO: make this configurable?
let max_check = max_check.min(4096);
let mut bytes = Vec::new();
let mut checked = 0;
loop {
bytes.resize((checked + 256).min(max_check), 0);
let read = cache.read.read(&mut bytes[checked..]).map_err(|_| ())?;
if read == 0 {
return Err(());
}
if let Some(len) = memchr::memchr(delimiter, &bytes[checked..][..read]) {
bytes.truncate(checked + len);
break entry.insert(bytes.into_boxed_slice());
}
checked += read;
if checked >= max_check {
return Err(());
}
}
}
};
// Extend the lifetime to that of self.
// This is OK because we never mutate or remove entries.
Ok(unsafe { mem::transmute::<&[u8], &[u8]>(buf) })
}
}
/// An implementation of `ReadRef` for a range of data in a stream that
/// implements `Read + Seek`.
///
/// Shares an underlying `ReadCache` with a lifetime of `'a`.
#[derive(Debug)]
pub struct ReadCacheRange<'a, R: Read + Seek> {
r: &'a ReadCache<R>,
offset: u64,
size: u64,
}
impl<'a, R: Read + Seek> Clone for ReadCacheRange<'a, R> {
fn clone(&self) -> Self {
Self {
r: self.r,
offset: self.offset,
size: self.size,
}
}
}
impl<'a, R: Read + Seek> Copy for ReadCacheRange<'a, R> {}
impl<'a, R: Read + Seek> ReadRef<'a> for ReadCacheRange<'a, R> {
fn len(self) -> Result<u64, ()> {
Ok(self.size)
}
fn read_bytes_at(self, offset: u64, size: u64) -> Result<&'a [u8], ()> {
if size == 0 {
return Ok(&[]);
}
let end = offset.checked_add(size).ok_or(())?;
if end > self.size {
return Err(());
}
let r_offset = self.offset.checked_add(offset).ok_or(())?;
self.r.read_bytes_at(r_offset, size)
}
fn read_bytes_at_until(self, range: Range<u64>, delimiter: u8) -> Result<&'a [u8], ()> {
let r_start = self.offset.checked_add(range.start).ok_or(())?;
let r_end = self.offset.checked_add(range.end).ok_or(())?;
let bytes = self.r.read_bytes_at_until(r_start..r_end, delimiter)?;
let size = bytes.len().try_into().map_err(|_| ())?;
let end = range.start.checked_add(size).ok_or(())?;
if end > self.size {
return Err(());
}
Ok(bytes)
}
}
|
