rust_cascade/src/lib.rs

extern crate byteorder;
extern crate digest;
extern crate murmurhash3;
extern crate sha2;

use byteorder::ReadBytesExt;
use murmurhash3::murmurhash3_x86_32;
use sha2::{Digest, Sha256};
use std::convert::{TryFrom, TryInto};
use std::fmt;
use std::io::{Error, ErrorKind};

/// Helper struct to provide read-only bit access to a slice of bytes.
struct BitSlice<'a> {
    /// The slice of bytes we're interested in.
    bytes: &'a [u8],
    /// The number of bits that are valid to access in the slice.
    /// Not necessarily equal to `bytes.len() * 8`, but it will not be greater than that.
    bit_len: usize,
}

impl<'a> BitSlice<'a> {
    /// Creates a new `BitSlice` of the given bit length over the given slice of data.
    /// Panics if the indicated bit length is larger than fits in the slice.
    ///
    /// # Arguments
    /// * `bytes` - The slice of bytes we need bit-access to
    /// * `bit_len` - The number of bits that are valid to access in the slice
    fn new(bytes: &'a [u8], bit_len: usize) -> BitSlice<'a> {
        if bit_len > bytes.len() * 8 {
            panic!(
                "bit_len too large for given data: {} > {} * 8",
                bit_len,
                bytes.len()
            );
        }
        BitSlice { bytes, bit_len }
    }

    /// Get the value of the specified bit.
    /// Panics if the specified bit is out of range for the number of bits in this instance.
    ///
    /// # Arguments
    /// * `bit_index` - The bit index to access
    fn get(&self, bit_index: usize) -> bool {
        if bit_index >= self.bit_len {
            panic!(
                "bit index out of range for bit slice: {} >= {}",
                bit_index, self.bit_len
            );
        }
        let byte_index = bit_index / 8;
        let final_bit_index = bit_index % 8;
        let byte = self.bytes[byte_index];
        let test_value = match final_bit_index {
            0 => byte & 0b0000_0001u8,
            1 => byte & 0b0000_0010u8,
            2 => byte & 0b0000_0100u8,
            3 => byte & 0b0000_1000u8,
            4 => byte & 0b0001_0000u8,
            5 => byte & 0b0010_0000u8,
            6 => byte & 0b0100_0000u8,
            7 => byte & 0b1000_0000u8,
            _ => panic!("impossible final_bit_index value: {}", final_bit_index),
        };
        test_value > 0
    }
}

/// A Bloom filter representing a specific level in a multi-level cascading Bloom filter.
struct Bloom<'a> {
    /// What level this filter is in
    level: u8,
    /// How many hash functions this filter uses
    n_hash_funcs: u32,
    /// The bit length of the filter
    size: u32,
    /// The data of the filter
    bit_slice: BitSlice<'a>,
    /// The hash algorithm enumeration in use
    hash_algorithm: HashAlgorithm,
}

#[repr(u8)]
#[derive(Copy, Clone)]
/// These enumerations need to match the python filter-cascade project:
/// https://github.com/mozilla/filter-cascade/blob/v0.3.0/filtercascade/fileformats.py
enum HashAlgorithm {
    MurmurHash3 = 1,
    Sha256 = 2,
}

impl fmt::Display for HashAlgorithm {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", *self as u8)
    }
}

impl TryFrom<u8> for HashAlgorithm {
    type Error = ();
    fn try_from(value: u8) -> Result<HashAlgorithm, ()> {
        match value {
            // Naturally, these need to match the enum declaration
            1 => Ok(Self::MurmurHash3),
            2 => Ok(Self::Sha256),
            _ => Err(()),
        }
    }
}

impl<'a> Bloom<'a> {
    /// Attempts to decode and return a pair that consists of the Bloom filter represented by the
    /// given bytes and any remaining unprocessed bytes in the given bytes.
    ///
    /// # Arguments
    /// * `bytes` - The encoded representation of this Bloom filter. May include additional data
    /// describing further Bloom filters. Any additional data is returned unconsumed.
    /// The format of an encoded Bloom filter is:
    /// [1 byte] - the hash algorithm to use in the filter
    /// [4 little endian bytes] - the length in bits of the filter
    /// [4 little endian bytes] - the number of hash functions to use in the filter
    /// [1 byte] - which level in the cascade this filter is
    /// [variable length bytes] - the filter itself (the length is determined by Ceiling(bit length
    /// / 8)
    pub fn from_bytes(bytes: &'a [u8]) -> Result<(Bloom<'a>, &'a [u8]), Error> {
        let mut cursor = bytes;
        // Load the layer metadata. bloomer.py writes size, nHashFuncs and level as little-endian
        // unsigned ints.
        let hash_algorithm_val = cursor.read_u8()?;
        let hash_algorithm = match HashAlgorithm::try_from(hash_algorithm_val) {
            Ok(algo) => algo,
            Err(()) => {
                return Err(Error::new(
                    ErrorKind::InvalidData,
                    "Unexpected hash algorithm",
                ))
            }
        };

        let size = cursor.read_u32::<byteorder::LittleEndian>()?;
        let n_hash_funcs = cursor.read_u32::<byteorder::LittleEndian>()?;
        let level = cursor.read_u8()?;

        let shifted_size = size.wrapping_shr(3) as usize;
        let byte_count = if size % 8 != 0 {
            shifted_size + 1
        } else {
            shifted_size
        };
        if byte_count > cursor.len() {
            return Err(Error::new(
                ErrorKind::InvalidData,
                "Invalid Bloom filter: too short",
            ));
        }
        let (bits_bytes, rest_of_bytes) = cursor.split_at(byte_count);
        let bloom = Bloom {
            level,
            n_hash_funcs,
            size,
            bit_slice: BitSlice::new(bits_bytes, size as usize),
            hash_algorithm,
        };
        Ok((bloom, rest_of_bytes))
    }

    fn hash(&self, n_fn: u32, key: &[u8], salt: Option<&[u8]>) -> u32 {
        match self.hash_algorithm {
            HashAlgorithm::MurmurHash3 => {
                if salt.is_some() {
                    panic!("murmur does not support salts")
                }
                let hash_seed = (n_fn << 16) + self.level as u32;
                murmurhash3_x86_32(key, hash_seed) % self.size
            }
            HashAlgorithm::Sha256 => {
                let mut hasher = Sha256::new();
                if let Some(salt_bytes) = salt {
                    hasher.input(salt_bytes)
                }
                hasher.input(n_fn.to_le_bytes());
                hasher.input(self.level.to_le_bytes());
                hasher.input(key);

                u32::from_le_bytes(
                    hasher.result()[0..4]
                        .try_into()
                        .expect("sha256 should have given enough bytes"),
                ) % self.size
            }
        }
    }

    /// Test for the presence of a given sequence of bytes in this Bloom filter.
    ///
    /// # Arguments
    /// `item` - The slice of bytes to test for
    pub fn has(&self, item: &[u8], salt: Option<&[u8]>) -> bool {
        for i in 0..self.n_hash_funcs {
            if !self.bit_slice.get(self.hash(i, item, salt) as usize) {
                return false;
            }
        }
        true
    }
}

impl<'a> fmt::Display for Bloom<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(
            f,
            "level={} n_hash_funcs={} hash_algorithm={} size={}",
            self.level, self.n_hash_funcs, self.hash_algorithm, self.size
        )
    }
}

/// A multi-level cascading Bloom filter.
pub struct Cascade<'a> {
    /// The Bloom filter for this level in the cascade
    filter: Bloom<'a>,
    /// The next (lower) level in the cascade
    child_layer: Option<Box<Cascade<'a>>>,
    /// The salt in use, if any
    salt: Option<&'a [u8]>,
    /// Whether the logic should be inverted
    inverted: bool,
}

impl<'a> Cascade<'a> {
    /// Attempts to decode and return a multi-level cascading Bloom filter. NB: `Cascade` does not
    /// take ownership of the given data. This is to facilitate decoding cascading filters
    /// backed by memory-mapped files.
    ///
    /// # Arguments
    /// `bytes` - The encoded representation of the Bloom filters in this cascade. Starts with 2
    /// little endian bytes indicating the version. The current version is 2. The Python
    /// filter-cascade project defines the formats, see
    /// https://github.com/mozilla/filter-cascade/blob/v0.3.0/filtercascade/fileformats.py
    ///
    /// May be of length 0, in which case `None` is returned.
    pub fn from_bytes(bytes: &'a [u8]) -> Result<Option<Box<Cascade<'a>>>, Error> {
        if bytes.is_empty() {
            return Ok(None);
        }
        let mut cursor = bytes;
        let version = cursor.read_u16::<byteorder::LittleEndian>()?;
        let mut salt = None;
        let mut inverted = false;

        if version >= 2 {
            inverted = cursor.read_u8()? != 0;
            let salt_len = cursor.read_u8()? as usize;

            if salt_len > cursor.len() {
                return Err(Error::new(
                    ErrorKind::InvalidData,
                    "Invalid Bloom filter: too short",
                ));
            }

            let (salt_bytes, remaining_bytes) = cursor.split_at(salt_len);
            if salt_len > 0 {
                salt = Some(salt_bytes)
            }
            cursor = remaining_bytes;
        }

        if version > 2 {
            return Err(Error::new(
                ErrorKind::InvalidData,
                format!("Invalid version: {}", version),
            ));
        }

        Cascade::child_layer_from_bytes(cursor, salt, inverted)
    }

    fn child_layer_from_bytes(
        bytes: &'a [u8],
        salt: Option<&'a [u8]>,
        inverted: bool,
    ) -> Result<Option<Box<Cascade<'a>>>, Error> {
        if bytes.is_empty() {
            return Ok(None);
        }
        let (filter, rest_of_bytes) = Bloom::from_bytes(bytes)?;
        Ok(Some(Box::new(Cascade {
            filter,
            child_layer: Cascade::child_layer_from_bytes(rest_of_bytes, salt, inverted)?,
            salt,
            inverted,
        })))
    }

    /// Determine if the given sequence of bytes is in the cascade.
    ///
    /// # Arguments
    /// `entry` - The slice of bytes to test for
    pub fn has(&self, entry: &[u8]) -> bool {
        let result = self.has_internal(entry);
        if self.inverted {
            return !result;
        }
        result
    }

    pub fn has_internal(&self, entry: &[u8]) -> bool {
        if self.filter.has(&entry, self.salt) {
            match self.child_layer {
                Some(ref child) => {
                    let child_value = !child.has_internal(entry);
                    return child_value;
                }
                None => {
                    return true;
                }
            }
        }
        false
    }
}

impl<'a> fmt::Display for Cascade<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(
            f,
            "salt={:?} inverted={} filter=[{}] ",
            self.salt, self.inverted, self.filter
        )?;
        match &self.child_layer {
            Some(layer) => write!(f, "[child={}]", layer),
            None => Ok(()),
        }
    }
}

#[cfg(test)]
mod tests {
    use Bloom;
    use Cascade;

    #[test]
    fn bloom_v1_test_from_bytes() {
        let src: Vec<u8> = vec![
            0x01, 0x09, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x41, 0x00,
        ];

        match Bloom::from_bytes(&src) {
            Ok((bloom, rest_of_bytes)) => {
                assert!(rest_of_bytes.len() == 0);
                assert!(bloom.has(b"this", None) == true);
                assert!(bloom.has(b"that", None) == true);
                assert!(bloom.has(b"other", None) == false);
            }
            Err(_) => {
                panic!("Parsing failed");
            }
        };

        let short: Vec<u8> = vec![
            0x01, 0x09, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x41,
        ];
        assert!(Bloom::from_bytes(&short).is_err());
    }

    #[test]
    fn bloom_v3_unsupported() {
        let src: Vec<u8> = vec![0x03, 0x01, 0x00];
        assert!(Bloom::from_bytes(&src).is_err());
    }

    #[test]
    fn cascade_v1_murmur_from_file_bytes_test() {
        let v = include_bytes!("../test_data/test_v1_murmur_mlbf");
        let cascade = Cascade::from_bytes(v)
            .expect("parsing Cascade should succeed")
            .expect("Cascade should be Some");
        // Key format is SHA256(issuer SPKI) + serial number
        #[rustfmt::skip]
        let key_for_revoked_cert_1 =
            [ 0x2e, 0xb2, 0xd5, 0xa8, 0x60, 0xfe, 0x50, 0xe9, 0xc2, 0x42, 0x36, 0x85, 0x52, 0x98,
              0x01, 0x50, 0xe4, 0x5d, 0xb5, 0x32, 0x1a, 0x5b, 0x00, 0x5e, 0x26, 0xd6, 0x76, 0x25,
              0x3a, 0x40, 0x9b, 0xf5,
              0x06, 0x2d, 0xf5, 0x68, 0xa0, 0x51, 0x31, 0x08, 0x20, 0xd7, 0xec, 0x43, 0x27, 0xe1,
              0xba, 0xfd ];
        assert!(cascade.has(&key_for_revoked_cert_1));
        #[rustfmt::skip]
        let key_for_revoked_cert_2 =
            [ 0xf1, 0x1c, 0x3d, 0xd0, 0x48, 0xf7, 0x4e, 0xdb, 0x7c, 0x45, 0x19, 0x2b, 0x83, 0xe5,
              0x98, 0x0d, 0x2f, 0x67, 0xec, 0x84, 0xb4, 0xdd, 0xb9, 0x39, 0x6e, 0x33, 0xff, 0x51,
              0x73, 0xed, 0x69, 0x8f,
              0x00, 0xd2, 0xe8, 0xf6, 0xaa, 0x80, 0x48, 0x1c, 0xd4 ];
        assert!(cascade.has(&key_for_revoked_cert_2));
        #[rustfmt::skip]
        let key_for_valid_cert =
            [ 0x99, 0xfc, 0x9d, 0x40, 0xf1, 0xad, 0xb1, 0x63, 0x65, 0x61, 0xa6, 0x1d, 0x68, 0x3d,
              0x9e, 0xa6, 0xb4, 0x60, 0xc5, 0x7d, 0x0c, 0x75, 0xea, 0x00, 0xc3, 0x41, 0xb9, 0xdf,
              0xb9, 0x0b, 0x5f, 0x39,
              0x0b, 0x77, 0x75, 0xf7, 0xaf, 0x9a, 0xe5, 0x42, 0x65, 0xc9, 0xcd, 0x32, 0x57, 0x10,
              0x77, 0x8e ];
        assert!(!cascade.has(&key_for_valid_cert));

        let v = include_bytes!("../test_data/test_v1_murmur_short_mlbf");
        assert!(Cascade::from_bytes(v).is_err());
    }

    #[test]
    fn cascade_v2_sha256_from_file_bytes_test() {
        let v = include_bytes!("../test_data/test_v2_sha256_mlbf");
        let cascade = Cascade::from_bytes(v)
            .expect("parsing Cascade should succeed")
            .expect("Cascade should be Some");

        assert!(cascade.salt == None);
        assert!(cascade.inverted == false);
        assert!(cascade.has(b"this") == true);
        assert!(cascade.has(b"that") == true);
        assert!(cascade.has(b"other") == false);
    }

    #[test]
    fn cascade_v2_sha256_with_salt_from_file_bytes_test() {
        let v = include_bytes!("../test_data/test_v2_sha256_salt_mlbf");
        let cascade = Cascade::from_bytes(v)
            .expect("parsing Cascade should succeed")
            .expect("Cascade should be Some");

        assert!(cascade.salt == Some(b"nacl"));
        assert!(cascade.inverted == false);
        assert!(cascade.has(b"this") == true);
        assert!(cascade.has(b"that") == true);
        assert!(cascade.has(b"other") == false);
    }

    #[test]
    fn cascade_v2_murmur_from_file_bytes_test() {
        let v = include_bytes!("../test_data/test_v2_murmur_mlbf");
        let cascade = Cascade::from_bytes(v)
            .expect("parsing Cascade should succeed")
            .expect("Cascade should be Some");

        assert!(cascade.salt == None);
        assert!(cascade.inverted == false);
        assert!(cascade.has(b"this") == true);
        assert!(cascade.has(b"that") == true);
        assert!(cascade.has(b"other") == false);
    }

    #[test]
    fn cascade_v2_murmur_inverted_from_file_bytes_test() {
        let v = include_bytes!("../test_data/test_v2_murmur_inverted_mlbf");
        let cascade = Cascade::from_bytes(v)
            .expect("parsing Cascade should succeed")
            .expect("Cascade should be Some");

        assert!(cascade.salt == None);
        assert!(cascade.inverted == true);
        assert!(cascade.has(b"this") == true);
        assert!(cascade.has(b"that") == true);
        assert!(cascade.has(b"other") == false);
    }

    #[test]
    fn cascade_v2_sha256_inverted_from_file_bytes_test() {
        let v = include_bytes!("../test_data/test_v2_sha256_inverted_mlbf");
        let cascade = Cascade::from_bytes(v)
            .expect("parsing Cascade should succeed")
            .expect("Cascade should be Some");

        assert!(cascade.salt == None);
        assert!(cascade.inverted == true);
        assert!(cascade.has(b"this") == true);
        assert!(cascade.has(b"that") == true);
        assert!(cascade.has(b"other") == false);
    }
}