bgpkit-parser 0.9.0-alpha-3

use bgp_models::bgp::*;
use bgp_models::network::*;
use byteorder::{ReadBytesExt, BE};
use num_traits::FromPrimitive;
use std::io::{Cursor, Seek, SeekFrom};

use crate::error::ParserError;
use crate::parser::{parse_nlri_list, AttributeParser, ReadUtils};
use log::warn;

/// BGP message
///
/// Format:
/// ```text
/// 0                   1                   2                   3
/// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// |                                                               |
/// +                                                               +
/// |                                                               |
/// +                                                               +
/// |                           Marker                              |
/// +                                                               +
/// |                                                               |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// |          Length               |      Type     |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// ```
pub fn parse_bgp_message(
    data: &[u8],
    add_path: bool,
    asn_len: &AsnLength,
) -> Result<BgpMessage, ParserError> {
    let total_size = data.len();
    let mut input = Cursor::new(data);
    // https://tools.ietf.org/html/rfc4271#section-4
    // 16 (4 x 4 bytes) octets marker
    input.read_32b()?;
    input.read_32b()?;
    input.read_32b()?;
    input.read_32b()?;
    /*
    This 2-octet unsigned integer indicates the total length of the
    message, including the header in octets.  Thus, it allows one
    to locate the (Marker field of the) next message in the TCP
    stream.  The value of the Length field MUST always be at least
    19 and no greater than 4096, and MAY be further constrained,
    depending on the message type.  "padding" of extra data after
    the message is not allowed.  Therefore, the Length field MUST
    have the smallest value required, given the rest of the
    message.
    */
    let length = input.read_u16::<BE>()?;
    if !(19..=4096).contains(&length) {
        return Err(ParserError::ParseError(format!(
            "invalid BGP message length {}",
            length
        )));
    }

    let bgp_msg_length = if (length as usize) > total_size {
        // return Err(ParserError::TruncatedMsg(format!("Truncated message: {} bytes available, {} bytes to read", total_size, length)))
        (total_size - 19) as u64
    } else {
        (length - 19) as u64
    };

    let msg_type: BgpMessageType = match BgpMessageType::from_u8(input.read_8b()?) {
        Some(t) => t,
        None => {
            return Err(ParserError::ParseError(
                "Unknown BGP Message Type".to_string(),
            ))
        }
    };

    // TODO: make sure we don't read over the bound
    // let mut bgp_msg_input = input.take(bgp_msg_length);
    Ok(match msg_type {
        BgpMessageType::OPEN => BgpMessage::Open(parse_bgp_open_message(&mut input)?),
        BgpMessageType::UPDATE => BgpMessage::Update(parse_bgp_update_message(
            &mut input,
            add_path,
            asn_len,
            bgp_msg_length,
        )?),
        BgpMessageType::NOTIFICATION => {
            BgpMessage::Notification(parse_bgp_notification_message(&mut input, bgp_msg_length)?)
        }
        BgpMessageType::KEEPALIVE => BgpMessage::KeepAlive(BgpKeepAliveMessage {}),
    })
}

/// Parse BGP NOTIFICATION messages.
///
/// The BGP NOTIFICATION messages contains BGP error codes received from a connected BGP router. The
/// error code is parsed into [BgpError] data structure and any unknown codes will produce warning
/// messages, but not critical errors.
pub fn parse_bgp_notification_message(
    input: &mut Cursor<&[u8]>,
    bgp_msg_length: u64,
) -> Result<BgpNotificationMessage, ParserError> {
    let error_code = input.read_8b()?;
    let error_subcode = input.read_8b()?;
    let error_type = match parse_error_codes(&error_code, &error_subcode) {
        Ok(t) => Some(t),
        Err(e) => {
            warn!("error parsing BGP notification error code: {}", e);
            None
        }
    };

    let data = input.read_n_bytes((bgp_msg_length - 2) as usize)?;
    Ok(BgpNotificationMessage {
        error_code,
        error_subcode,
        error_type,
        data,
    })
}

/// Parse BGP OPEN messages.
///
/// The parsing of BGP OPEN messages also includes decoding the BGP capabilities.
pub fn parse_bgp_open_message(input: &mut Cursor<&[u8]>) -> Result<BgpOpenMessage, ParserError> {
    let version = input.read_8b()?;
    let asn = Asn {
        asn: input.read_u16::<BE>()? as u32,
        len: AsnLength::Bits16,
    };
    let hold_time = input.read_u16::<BE>()?;
    let sender_ip = input.read_ipv4_address()?;
    let opt_params_len = input.read_8b()?;

    let pos_end = input.position() + opt_params_len as u64;

    let mut extended_length = false;
    let mut first = true;

    let mut params: Vec<OptParam> = vec![];
    while input.position() < pos_end {
        let param_type = input.read_8b()?;
        if first {
            // first parameter, check if it is extended length message
            if opt_params_len == 255 && param_type == 255 {
                extended_length = true;
                // TODO: handle extended length
                break;
            } else {
                first = false;
            }
        }
        // reaching here means all the remain params are regular non-extended-length parameters

        let parm_length = input.read_8b()?;
        // https://tools.ietf.org/html/rfc3392
        // https://www.iana.org/assignments/bgp-parameters/bgp-parameters.xhtml#bgp-parameters-11

        let param_value = match param_type {
            2 => {
                // capability codes:
                // https://www.iana.org/assignments/capability-codes/capability-codes.xhtml#capability-codes-2
                let code = input.read_8b()?;
                let len = input.read_8b()?;
                let value = input.read_n_bytes(len as usize)?;

                let capability_type = match parse_capability(&code) {
                    Ok(t) => Some(t),
                    Err(e) => {
                        warn!("error parsing BGP capability code: {}", e.to_string());
                        None
                    }
                };

                ParamValue::Capability(Capability {
                    code,
                    len,
                    value,
                    capability_type,
                })
            }
            _ => {
                // unsupported param, read as raw bytes
                let bytes = input.read_n_bytes(parm_length as usize)?;
                ParamValue::Raw(bytes)
            }
        };
        params.push(OptParam {
            param_type,
            param_len: parm_length as u16,
            param_value,
        });
    }

    Ok(BgpOpenMessage {
        version,
        asn,
        hold_time,
        sender_ip,
        extended_length,
        opt_params: params,
    })
}

/// read nlri portion of a bgp update message.
fn read_nlri(
    input: &mut Cursor<&[u8]>,
    length: usize,
    afi: &Afi,
    add_path: bool,
) -> Result<Vec<NetworkPrefix>, ParserError> {
    if length == 0 {
        return Ok(vec![]);
    }
    if length == 1 {
        // 1 byte does not make sense
        warn!("seeing strange one-byte NLRI field");
        input.read_8b().unwrap();
        return Ok(vec![]);
    }

    parse_nlri_list(input, add_path, afi, length as u64)
}

/// read bgp update message.
pub fn parse_bgp_update_message(
    input: &mut Cursor<&[u8]>,
    add_path: bool,
    asn_len: &AsnLength,
    bgp_msg_length: u64,
) -> Result<BgpUpdateMessage, ParserError> {
    // AFI for routes out side attributes are IPv4 ONLY.
    let afi = Afi::Ipv4;

    // parse withdrawn prefixes nlri
    let withdrawn_length = input.read_u16::<BE>()? as u64;
    let withdrawn_prefixes = read_nlri(input, withdrawn_length as usize, &afi, add_path)?;

    // parse attributes
    let attribute_length = input.read_u16::<BE>()? as usize;
    let attr_parser = AttributeParser::new(add_path);

    let pos_start = input.position() as usize;
    let pos_end = pos_start + attribute_length;
    let attr_data_slice = &input.get_ref()[pos_start..pos_end];
    let attributes = attr_parser.parse_attributes(attr_data_slice, asn_len, None, None, None)?;
    input.seek(SeekFrom::Start(pos_end as u64))?;

    // parse announced prefixes nlri
    let nlri_length = bgp_msg_length - 4 - withdrawn_length - attribute_length as u64;
    let announced_prefixes = read_nlri(input, nlri_length as usize, &afi, add_path)?;

    Ok(BgpUpdateMessage {
        withdrawn_prefixes,
        attributes,
        announced_prefixes,
    })
}