deflate/
stored_block.rs

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1use std::io::Write;
2use std::io;
3use std::u16;
4use bitstream::LsbWriter;
5use byteorder::{LittleEndian, WriteBytesExt};
6
7#[cfg(test)]
8const BLOCK_SIZE: u16 = 32000;
9
10const STORED_FIRST_BYTE: u8 = 0b0000_0000;
11pub const STORED_FIRST_BYTE_FINAL: u8 = 0b0000_0001;
12pub const MAX_STORED_BLOCK_LENGTH: usize = (u16::MAX as usize) / 2;
13
14pub fn write_stored_header(writer: &mut LsbWriter, final_block: bool) {
15    let header = if final_block {
16        STORED_FIRST_BYTE_FINAL
17    } else {
18        STORED_FIRST_BYTE
19    };
20    // Write the block header
21    writer.write_bits(header.into(), 3);
22    // Flush the writer to make sure we are aligned to the byte boundary.
23    writer.flush_raw();
24}
25
26// Compress one stored block (excluding the header)
27pub fn compress_block_stored<W: Write>(input: &[u8], writer: &mut W) -> io::Result<usize> {
28    if input.len() > u16::max_value() as usize {
29        return Err(io::Error::new(
30            io::ErrorKind::InvalidInput,
31            "Stored block too long!",
32        ));
33    };
34    // The header is written before this function.
35    // The next two bytes indicates the length
36    writer.write_u16::<LittleEndian>(input.len() as u16)?;
37    // the next two after the length is the ones complement of the length
38    writer.write_u16::<LittleEndian>(!input.len() as u16)?;
39    // After this the data is written directly with no compression
40    writer.write(input)
41}
42
43#[cfg(test)]
44pub fn compress_data_stored(input: &[u8]) -> Vec<u8> {
45    let block_length = BLOCK_SIZE as usize;
46
47    let mut output = Vec::with_capacity(input.len() + 2);
48    let mut i = input.chunks(block_length).peekable();
49    while let Some(chunk) = i.next() {
50        let last_chunk = i.peek().is_none();
51        // First bit tells us if this is the final chunk
52        // the next two details compression type (none in this case)
53        let first_byte = if last_chunk {
54            STORED_FIRST_BYTE_FINAL
55        } else {
56            STORED_FIRST_BYTE
57        };
58        output.write(&[first_byte]).unwrap();
59
60        compress_block_stored(chunk, &mut output).unwrap();
61    }
62    output
63}
64
65
66#[cfg(test)]
67mod test {
68    use super::*;
69    use test_utils::decompress_to_end;
70
71    #[test]
72    fn no_compression_one_chunk() {
73        let test_data = vec![1u8, 2, 3, 4, 5, 6, 7, 8];
74        let compressed = compress_data_stored(&test_data);
75        let result = decompress_to_end(&compressed);
76        assert_eq!(test_data, result);
77    }
78
79    #[test]
80    fn no_compression_multiple_chunks() {
81        let test_data = vec![32u8; 40000];
82        let compressed = compress_data_stored(&test_data);
83        let result = decompress_to_end(&compressed);
84        assert_eq!(test_data, result);
85    }
86
87    #[test]
88    fn no_compression_string() {
89        let test_data = String::from(
90            "This is some text, this is some more text, this is even \
91             more text, lots of text here.",
92        ).into_bytes();
93        let compressed = compress_data_stored(&test_data);
94        let result = decompress_to_end(&compressed);
95        assert_eq!(test_data, result);
96    }
97}
deflate/stored_block.rs

deflate/
stored_block.rs
