squinter 0.3.1

Library to interface with SquashFS filesystems
Documentation 
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
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231

use std::cmp;
use std::collections::HashMap;
use std::io::{self, Cursor, Read, Seek, SeekFrom};

use super::readermux::{ReaderClient, ReaderMux};
use super::compressed::CompressedBlockReader;
use super::superblock::Compressor;

/// A seekable reader that wraps a forward-only backing-store reader. A simple Cursor provides the 
/// external reader, but the inner reader is read and appended to the Cursor whenever the requested
/// read would advance beyond the end of the Cursor's data.
/// When BorrowedBuf comes off nightly, it may be appropriate to use for this.
#[derive(Debug)]
pub struct CachingReader<R> {
    inner: R,
    cache: Cursor<Vec<u8>>,
}

impl<R:Read> CachingReader<R> {
    pub fn new(inner: R) -> Self {
        Self {
            inner: inner,
            cache: Cursor::new(Vec::new()),
        }
    }

    pub fn new_with_capacity(inner: R, cap: usize) -> Self {
        Self {
            inner: inner,
            cache: Cursor::new(Vec::with_capacity(cap)),
        }
    }
}

impl<R:Read> Read for CachingReader<R> {
    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
        let initial_pos = self.cache.position();
        let end_pos = initial_pos + (buf.len() as u64);

        // If we need to read more inner data, first do that and add it to the cache
        if end_pos > self.cache.get_ref().len() as u64 {
            let target_read_len = end_pos - (self.cache.get_ref().len() as u64);
            self.cache.seek(SeekFrom::End(0))?;
            io::copy(&mut self.inner.by_ref().take(target_read_len), &mut self.cache)?;
            self.cache.set_position(initial_pos);
        }

        self.cache.read(buf)
    }
}

impl<R> Seek for CachingReader<R> {
    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
        self.cache.seek(pos)
    }
}


/// A store of fragment blocks. Users can request a specific fragment by block, offset, and length
/// The cache will provide a reader that is backed by the memory buffer and will read additional
/// data from the inner reader as needed to fulfill reads.
#[derive(Debug)]
pub struct FragmentBlockCache<R: Read+Seek> {
    inner: ReaderMux<R>,
    compressor: Compressor,
    block_readers: HashMap<u64, ReaderMux<CachingReader<CompressedBlockReader<ReaderClient<R>>>>>,
}

impl<R:Read+Seek> FragmentBlockCache<R> {
    pub fn new(inner: R, compressor: Compressor) -> Self {
        Self {
            inner: ReaderMux::new(inner),
            compressor,
            block_readers: HashMap::new(),
        }
    }

    pub fn get_fragment_reader(&mut self, block_addr: u64, block_size: u64, block_uncompressed_size: u64, offset: u64, len: u64)
        -> io::Result<FragmentReader<ReaderClient<CachingReader<CompressedBlockReader<ReaderClient<R>>>>>>
    {
        let block_reader = match self.block_readers.get_mut(&block_addr) {
            Some(r) => r,
            None => {
                let r = self.create_block_reader(block_addr, block_size, block_uncompressed_size)?;
                self.block_readers.insert(block_addr, r);
                self.block_readers.get_mut(&block_addr).unwrap()
            },
        };
        FragmentReader::new(block_reader.client(), offset, len)
    }

    fn create_block_reader(&mut self, block_addr: u64, block_size: u64, uncompressed_size: u64)
        -> io::Result<ReaderMux<CachingReader<CompressedBlockReader<ReaderClient<R>>>>>
    {
        let mut client_reader = self.inner.client();
        client_reader.seek(SeekFrom::Start(block_addr))?;
        let compressed_reader = CompressedBlockReader::new(client_reader, self.compressor, block_size, uncompressed_size)?;
        let caching_reader = CachingReader::new_with_capacity(compressed_reader, block_size as usize);
        Ok(ReaderMux::new(caching_reader))
    }
}

/// A fragment reader is a single-fragment view of a portion of a fragment block
#[derive(Debug)]
pub struct FragmentReader<R> {
    inner: R, // the backing reader
    offset: u64, // offset of the beginning of this reader within the inner reader
    len: u64, // length of this reader
    pos: u64, // 0-based position within this reader
}

impl<R:Read+Seek> FragmentReader<R> {
    pub fn new(mut inner: R, offset: u64, len: u64) -> io::Result<Self> {
        inner.seek(SeekFrom::Start(offset))?;
        Ok(Self {
            inner,
            offset,
            len,
            pos: 0,
        })
    }
}

impl<R:Read+Seek> Read for FragmentReader<R> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        if self.pos >= self.len {
            return Ok(0);
        }
        let max = cmp::min(buf.len() as u64, self.len-self.pos) as usize;
        let n = self.inner.read(&mut buf[..max])?;
        assert!(self.pos + n as u64 <= self.len);
        self.pos += n as u64;
        Ok(n)
    }
}

impl<R:Seek> Seek for FragmentReader<R> {
    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
        match pos {
            SeekFrom::Start(p) => {
                let n = self.inner.seek(SeekFrom::Start(self.offset+p))?;
                assert!(n >= self.offset);
                self.pos = n - self.offset;
                Ok(self.pos)
            },
            SeekFrom::End(p) => {
                assert!(self.len as i64 + p >= 0);
                let inner_pos = (self.offset+self.len) as i64 + p;
                let n = self.inner.seek(SeekFrom::Start(inner_pos as u64))?;
                assert!(n >= self.offset);
                self.pos = n - self.offset;
                Ok(self.pos)
            },
            SeekFrom::Current(p) => {
                assert!(self.pos as i64 + p >= 0);
                let n = self.inner.seek(SeekFrom::Current(p))?;
                assert!(n >= self.offset);
                self.pos = n - self.offset;
                Ok(self.pos)
            },
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io::Cursor;

    #[test]
    fn test_caching_reader() -> io::Result<()> {
        let data: Vec<u8> = (0..=255).collect();
        let backing_reader = Cursor::new((0..=255).collect::<Vec<u8>>());
        let mut caching_reader = CachingReader::new(backing_reader);
        let mut buf = [0; 8];

        assert_eq!(caching_reader.read(&mut buf)?, buf.len());
        println!("Read {:?}", &buf);
        assert!(buf.iter().eq(data[0..8].iter()));

        assert_eq!(caching_reader.read(&mut buf)?, buf.len());
        println!("Read {:?}", &buf);
        assert!(buf.iter().eq(data[8..16].iter()));

        caching_reader.seek(SeekFrom::Current(8))?;
        assert_eq!(caching_reader.read(&mut buf)?, buf.len());
        println!("Read {:?}", &buf);
        assert!(buf.iter().eq(data[24..32].iter()));

        caching_reader.seek(SeekFrom::Current(-16))?;
        assert_eq!(caching_reader.read(&mut buf)?, buf.len());
        println!("Read {:?}", &buf);
        assert!(buf.iter().eq(data[16..24].iter()));

        caching_reader.seek(SeekFrom::Start(252))?;
        assert_eq!(caching_reader.read(&mut buf)?, 4);
        println!("Read {:?}", &buf[0..4]);
        assert!(buf.iter().take(4).eq(data[252..=255].iter()));
        Ok(())
    }

    #[test]
    fn test_block_cache() -> io::Result<()> {
        let data: Vec<u8> = (0..=255).collect();
        let backing_reader = Cursor::new((0..=255).collect::<Vec<u8>>());
        let mut block_cache = FragmentBlockCache::new(backing_reader, Compressor::None);
        let mut buf = [0; 8];

        let mut frag_reader1 = block_cache.get_fragment_reader(32, 32, 32, 8, 16)?;
        let mut frag_reader2 = block_cache.get_fragment_reader(0, 32, 32, 0, 32)?;

        assert_eq!(frag_reader1.read(&mut buf)?, buf.len());
        println!("Read {:?}", &buf);
        assert!(buf.iter().eq(data[40..48].iter()));

        assert_eq!(frag_reader2.read(&mut buf)?, buf.len());
        println!("Read {:?}", &buf);
        assert!(buf.iter().eq(data[0..8].iter()));

        assert_eq!(frag_reader1.read(&mut buf)?, buf.len());
        println!("Read {:?}", &buf);
        assert!(buf.iter().eq(data[48..56].iter()));

        assert_eq!(frag_reader2.read(&mut buf)?, buf.len());
        println!("Read {:?}", &buf);
        assert!(buf.iter().eq(data[8..16].iter()));

        Ok(())
    }

}