Module bitstream_io::read

Traits and implementations for reading bits from a stream.

Example

Reading the initial STREAMINFO block from a FLAC file, as documented in its specification.

use std::io::{Cursor, Read};
use bitstream_io::{BigEndian, BitReader, BitRead, ByteReader, ByteRead, LittleEndian};

let flac: Vec<u8> = vec![0x66,0x4c,0x61,0x43,0x00,0x00,0x00,0x22,
                         0x10,0x00,0x10,0x00,0x00,0x06,0x06,0x00,
                         0x21,0x62,0x0a,0xc4,0x42,0xf0,0x00,0x04,
                         0xa6,0xcc,0xfa,0xf2,0x69,0x2f,0xfd,0xec,
                         0x2d,0x5b,0x30,0x01,0x76,0xb4,0x62,0x88,
                         0x7d,0x92,0x04,0x00,0x00,0x7a,0x20,0x00,
                         0x00,0x00,0x72,0x65,0x66,0x65,0x72,0x65,
                         0x6e,0x63,0x65,0x20,0x6c,0x69,0x62,0x46,
                         0x4c,0x41,0x43,0x20,0x31,0x2e,0x31,0x2e,
                         0x34,0x20,0x32,0x30,0x30,0x37,0x30,0x32,
                         0x31,0x33,0x04,0x00,0x00,0x00,0x16,0x00,
                         0x00,0x00,0x74,0x69,0x74,0x6c,0x65,0x3d,
                         0x32,0x63,0x68,0x20,0x34,0x34,0x31,0x30,
                         0x30,0x20,0x20,0x31,0x36,0x62,0x69,0x74,
                         0x10,0x00,0x00,0x00,0x61,0x6c,0x62,0x75,
                         0x6d,0x3d,0x54,0x65,0x73,0x74,0x20,0x41,
                         0x6c,0x62,0x75,0x6d,0x0f,0x00,0x00,0x00,
                         0x61,0x72,0x74,0x69,0x73,0x74,0x3d,0x41,
                         0x73,0x73,0x6f,0x72,0x74,0x65,0x64,0x0d,
                         0x00,0x00,0x00,0x74,0x72,0x61,0x63,0x6b,
                         0x6e,0x75,0x6d,0x62,0x65,0x72,0x3d,0x31];

#[derive(Debug, PartialEq, Eq)]
struct BlockHeader {
    last_block: bool,
    block_type: u8,
    block_size: u32,
}

impl BlockHeader {
    fn read<R: std::io::Read>(r: &mut BitReader<R, BigEndian>) -> std::io::Result<Self> {
        Ok(Self {
            last_block: r.read_bit()?,
            block_type: r.read(7)?,
            block_size: r.read(24)?,
        })
    }
}

#[derive(Debug, PartialEq, Eq)]
struct Streaminfo {
    minimum_block_size: u16,
    maximum_block_size: u16,
    minimum_frame_size: u32,
    maximum_frame_size: u32,
    sample_rate: u32,
    channels: u8,
    bits_per_sample: u8,
    total_samples: u64,
    md5: [u8; 16],
}

impl Streaminfo {
    fn read<R: std::io::Read>(r: &mut BitReader<R, BigEndian>) -> std::io::Result<Self> {
        Ok(Self {
            minimum_block_size: r.read(16)?,
            maximum_block_size: r.read(16)?,
            minimum_frame_size: r.read(24)?,
            maximum_frame_size: r.read(24)?,
            sample_rate: r.read(20)?,
            channels: r.read::<u8>(3)? + 1,
            bits_per_sample: r.read::<u8>(5)? + 1,
            total_samples: r.read(36)?,
            md5: r.read_to_bytes()?,
        })
    }
}

#[derive(Debug, PartialEq, Eq)]
struct VorbisComment {
    vendor: String,
    comment: Vec<String>,
}

impl VorbisComment {
   fn read<R: std::io::Read>(
       r: &mut ByteReader<R, LittleEndian>,
   ) -> Result<Self, Box<dyn std::error::Error>> {

       fn read_entry<R: std::io::Read>(
           r: &mut ByteReader<R, LittleEndian>,
       ) -> Result<String, Box<dyn std::error::Error>> {
           use std::convert::TryInto;
           let size = r.read::<u32>()?.try_into()?;
           Ok(String::from_utf8(r.read_to_vec(size)?)?)
       }

       Ok(Self {
           vendor: read_entry(r)?,
           comment: (0..r.read::<u32>()?)
               .map(|_| read_entry(r))
               .collect::<Result<Vec<_>, _>>()?,
       })
   }
}

let mut cursor = Cursor::new(&flac);

let mut reader = BitReader::endian(&mut cursor, BigEndian);

// stream marker
assert_eq!(&reader.read_to_bytes().unwrap(), b"fLaC");

// metadata block header
assert_eq!(
    BlockHeader::read(&mut reader).unwrap(),
    BlockHeader { last_block: false, block_type: 0, block_size: 34 }
);

// STREAMINFO block
assert_eq!(
    Streaminfo::read(&mut reader).unwrap(),
    Streaminfo {
        minimum_block_size: 4096,
        maximum_block_size: 4096,
        minimum_frame_size: 1542,
        maximum_frame_size: 8546,
        sample_rate: 44100,
        channels: 2,
        bits_per_sample: 16,
        total_samples: 304844,
        md5: *b"\xFA\xF2\x69\x2F\xFD\xEC\x2D\x5B\x30\x01\x76\xB4\x62\x88\x7D\x92",
    }
);

// metadata block header
assert_eq!(
    BlockHeader::read(&mut reader).unwrap(),
    BlockHeader { last_block: false, block_type: 4, block_size: 122 }
);

// VORBIS_COMMENT block (little endian)
assert_eq!(
   VorbisComment::read(&mut ByteReader::new(reader.reader().unwrap())).unwrap(),
   VorbisComment {
       vendor: "reference libFLAC 1.1.4 20070213".to_string(),
       comment: vec![
           "title=2ch 44100  16bit".to_string(),
           "album=Test Album".to_string(),
           "artist=Assorted".to_string(),
           "tracknumber=1".to_string(),
       ],
   }
);

Structs

BitReader

For reading non-aligned bits from a stream of bytes in a given endianness.

ByteReader

For reading aligned bytes from a stream of bytes in a given endianness.

Traits

BitRead

A trait for anything that can read a variable number of potentially un-aligned values from an input stream

ByteRead

A trait for anything that can read aligned values from an input stream

HuffmanRead

A trait for anything that can read Huffman codes of a given endianness from an input stream