simple-dns 0.13.0

use crate::{
    bytes_buffer::BytesBuffer,
    dns::WireFormat,
    lib::Write,
    lib::{BTreeMap, Cow, Vec},
    Name,
};

use super::{RR, TYPE};

/// A NSEC record see [rfc4034](https://datatracker.ietf.org/doc/html/rfc4034#section-4)
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
pub struct NSEC<'a> {
    /// The next owner name in the canonical ordering of the zone
    pub next_name: Name<'a>,
    /// The type bit maps representing the RR types present at the NSEC RR's owner name
    pub type_bit_maps: Vec<NsecTypeBitMap<'a>>,
}

/// A Type bit map entry in a NSEC record see [rfc4034](https://datatracker.ietf.org/doc/html/rfc4034#section-4.1.2)
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
pub struct NsecTypeBitMap<'a> {
    /// The window block number of this bit map
    pub window_block: u8,
    /// The bitmap containing the RR types present in this window block
    pub bitmap: Cow<'a, [u8]>,
}

impl RR for NSEC<'_> {
    const TYPE_CODE: u16 = 47;
}

impl<'a> WireFormat<'a> for NSEC<'a> {
    const MINIMUM_LEN: usize = 0;
    fn parse(data: &mut BytesBuffer<'a>) -> crate::Result<Self>
    where
        Self: Sized,
    {
        let next_name = Name::parse(data)?;
        let mut type_bit_maps = Vec::new();
        let mut prev_window_block = None;

        while data.has_remaining() {
            let window_block = data.get_u8()?;
            if let Some(prev_window_block) = prev_window_block {
                if window_block <= prev_window_block {
                    return Err(crate::SimpleDnsError::InvalidDnsPacket);
                }
            }

            prev_window_block = Some(window_block);

            let bitmap_length = data.get_u8()? as usize;
            if bitmap_length > 32 {
                return Err(crate::SimpleDnsError::InvalidDnsPacket);
            }

            let bitmap = data.get_slice(bitmap_length)?;

            type_bit_maps.push(NsecTypeBitMap {
                window_block,
                bitmap: Cow::Borrowed(bitmap),
            });
        }

        Ok(Self {
            next_name,
            type_bit_maps,
        })
    }

    fn write_to<T: Write>(&self, out: &mut T) -> crate::Result<()> {
        self.next_name.write_to(out)?;

        let mut sorted = self.type_bit_maps.clone();
        sorted.sort_by_key(|a| a.window_block);

        for record in sorted.iter() {
            out.write_all(&[record.window_block])?;
            out.write_all(&[record.bitmap.len() as u8])?;
            out.write_all(&record.bitmap)?;
        }

        Ok(())
    }

    fn len(&self) -> usize {
        // To calculate the len it is necessary to get the len of all the bitmaps in the nsec record
        // Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )+
        self.next_name.len()
            + self
                .type_bit_maps
                .iter()
                .map(|el| el.bitmap.len() + 2) // each type window has 2 bytes + bitmap data
                .sum::<usize>()
    }
}

impl<'a> NSEC<'a> {
    /// Constructs a new `NSEC` record with the given `next_name` and list of [`TYPE`]s.
    ///
    /// Bitmaps are constructed and windowed according to [RFC 4034 Section 4.1.2](https://datatracker.ietf.org/doc/html/rfc4034#section-4.1.2).
    pub fn from_types(next_name: Name<'a>, types: &[TYPE]) -> Self {
        let mut windows: BTreeMap<u8, [u8; 32]> = BTreeMap::new();
        let mut max_bytes: BTreeMap<u8, usize> = BTreeMap::new();

        for &ty in types {
            let type_code = u16::from(ty);
            let window = (type_code / 256) as u8;
            let offset_in_window = (type_code % 256) as usize;
            let byte_idx = offset_in_window / 8;
            let bit_idx = offset_in_window % 8;

            let bitmap = windows.entry(window).or_insert([0u8; 32]);
            bitmap[byte_idx] |= 0x80 >> bit_idx;

            let max_byte = max_bytes.entry(window).or_insert(0);
            if byte_idx > *max_byte {
                *max_byte = byte_idx;
            }
        }

        let type_bit_maps = windows
            .into_iter()
            .map(|(window_block, bitmap)| {
                let len = max_bytes.get(&window_block).copied().unwrap_or(0) + 1;
                NsecTypeBitMap {
                    window_block,
                    bitmap: Cow::Owned(bitmap[..len].to_vec()),
                }
            })
            .collect();

        Self {
            next_name,
            type_bit_maps,
        }
    }

    /// Returns `true` if the type bit maps indicate the presence of `ty`.
    pub fn contains(&self, ty: TYPE) -> bool {
        let type_code = u16::from(ty);
        let window = (type_code / 256) as u8;
        let offset_in_window = (type_code % 256) as usize;
        let byte_idx = offset_in_window / 8;
        let bit_mask = 0x80 >> (offset_in_window % 8);

        for map in &self.type_bit_maps {
            if map.window_block == window {
                return map
                    .bitmap
                    .get(byte_idx)
                    .is_some_and(|byte| (byte & bit_mask) != 0);
            }
        }
        false
    }

    /// Iterates over all [`TYPE`]s represented in this record's type bit maps.
    pub fn types(&self) -> impl Iterator<Item = TYPE> + '_ {
        self.type_bit_maps.iter().flat_map(|map| {
            let window_base = (map.window_block as u16) * 256;
            map.bitmap
                .iter()
                .enumerate()
                .flat_map(move |(byte_idx, &byte)| {
                    (0..8).filter_map(move |bit_idx| {
                        if (byte & (0x80 >> bit_idx)) != 0 {
                            let type_code = window_base + (byte_idx as u16) * 8 + (bit_idx as u16);
                            Some(TYPE::from(type_code))
                        } else {
                            None
                        }
                    })
                })
        })
    }

    /// Transforms the inner data into its owned type
    pub fn into_owned<'b>(self) -> NSEC<'b> {
        let type_bit_maps = self
            .type_bit_maps
            .into_iter()
            .map(|x| NsecTypeBitMap {
                window_block: x.window_block,
                bitmap: x.bitmap.into_owned().into(),
            })
            .collect();
        NSEC {
            next_name: self.next_name.into_owned(),
            type_bit_maps,
        }
    }
}

#[cfg(test)]
mod tests {

    use super::*;
    use crate::lib::vec;

    #[test]
    fn parse_and_write_nsec() {
        let nsec = NSEC {
            next_name: Name::new("host.example.com.").unwrap(),
            type_bit_maps: vec![NsecTypeBitMap {
                window_block: 0,
                bitmap: vec![64, 1, 0, 0, 0, 1].into(),
            }],
        };
        let mut data = Vec::new();
        nsec.write_to(&mut data).unwrap();

        let nsec = NSEC::parse(&mut data[..].into()).unwrap();
        assert_eq!(nsec.next_name, Name::new("host.example.com.").unwrap());
        assert_eq!(nsec.type_bit_maps.len(), 1);
        assert_eq!(nsec.type_bit_maps[0].window_block, 0);
        assert_eq!(nsec.type_bit_maps[0].bitmap, vec![64, 1, 0, 0, 0, 1]);
    }

    #[test]
    fn nsec_reports_correct_len() {
        let nsec = NSEC {
            next_name: Name::new("host.example.com.").unwrap(),
            type_bit_maps: vec![
                NsecTypeBitMap {
                    window_block: 0,
                    bitmap: vec![0x40, 0x01, 0x00, 0x00, 0x00, 0x01].into(),
                },
                NsecTypeBitMap {
                    window_block: 1,
                    bitmap: vec![0x40, 0x01, 0x00, 0x00, 0x00, 0x01].into(),
                },
            ],
        };

        let mut buffer = Vec::new();
        nsec.write_to(&mut buffer).unwrap();
        assert_eq!(buffer.len(), nsec.len());
    }

    #[test]
    #[cfg(feature = "std")]
    fn parse_sample() -> Result<(), Box<dyn std::error::Error>> {
        use crate::{rdata::RData, ResourceRecord};
        let sample_file = std::fs::read("samples/zonefile/NSEC.sample")?;

        let sample_rdata = match ResourceRecord::parse(&mut sample_file[..].into())?.rdata {
            RData::NSEC(rdata) => rdata,
            _ => unreachable!(),
        };

        assert_eq!(
            sample_rdata.next_name,
            Name::new("host.example.com.").unwrap()
        );
        assert_eq!(sample_rdata.type_bit_maps.len(), 1);
        assert_eq!(sample_rdata.type_bit_maps[0].window_block, 0);
        assert_eq!(
            sample_rdata.type_bit_maps[0].bitmap,
            vec![64, 1, 0, 0, 0, 1]
        );

        Ok(())
    }

    #[test]
    fn test_nsec_from_types_and_helpers() {
        let name = Name::new("host.example.com.").unwrap();
        let types = [TYPE::A, TYPE::MX, TYPE::NSEC, TYPE::Unknown(300)];
        let nsec = NSEC::from_types(name.clone(), &types);

        assert_eq!(nsec.next_name, name);
        assert_eq!(nsec.type_bit_maps.len(), 2);
        assert_eq!(nsec.type_bit_maps[0].window_block, 0);
        assert_eq!(nsec.type_bit_maps[0].bitmap, vec![64, 1, 0, 0, 0, 1]);
        assert_eq!(nsec.type_bit_maps[1].window_block, 1);

        assert!(nsec.contains(TYPE::A));
        assert!(nsec.contains(TYPE::MX));
        assert!(nsec.contains(TYPE::NSEC));
        assert!(nsec.contains(TYPE::Unknown(300)));
        assert!(!nsec.contains(TYPE::AAAA));
        assert!(!nsec.contains(TYPE::TXT));

        let recovered: Vec<_> = nsec.types().collect();
        assert_eq!(recovered, types);

        assert_eq!(u16::from(crate::CLASS::IN), 1);
        assert_eq!(u16::from(crate::CLASS::CS), 2);
    }
}