bgpkit-parser 0.9.0-alpha-2

use bgp_models::bgp::*;
use bgp_models::network::*;
use num_traits::FromPrimitive;

use crate::error::ParserError;
use crate::parser::{AttributeParser, DataBytes};
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(input: &mut DataBytes, add_path: bool, asn_len: &AsnLength, total_size: usize) -> Result<BgpMessage, ParserError> {
    // 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_16b()?;
    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()))
        }
    };

    // 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(input)?)
            }
            BgpMessageType::UPDATE => {
                BgpMessage::Update(parse_bgp_update_message(input, add_path, asn_len, bgp_msg_length)?)
            }
            BgpMessageType::NOTIFICATION => {
                BgpMessage::Notification(parse_bgp_notification_message(input, bgp_msg_length)?)
            }
            BgpMessageType::KEEPALIVE => {
                BgpMessage::KeepAlive(BgpKeepAliveMessage{})
            }
        }
    )
}

pub fn parse_bgp_notification_message(input: &mut DataBytes, bgp_msg_length: u64) -> Result<BgpNotificationMessage, ParserError> {
    let error_code = input.read_8b()?;
    let error_subcode = input.read_8b()?;
    let data = input.read_n_bytes((bgp_msg_length - 2) as usize)?;
    Ok(
        BgpNotificationMessage{
            error_code,
            error_subcode,
            error_type: None,
            data
        })
}

pub fn parse_bgp_open_message(input: &mut DataBytes) -> Result<BgpOpenMessage, ParserError> {
    let version = input.read_8b()?;
    let asn = Asn{asn: input.read_16b()? as u32, len: AsnLength::Bits16};
    let hold_time = input.read_16b()?;
    let sender_ip = input.read_ipv4_address()?;
    let opt_params_len = input.read_8b()?;

    let pos_end = input.pos + opt_params_len as usize;

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

    let mut params: Vec<OptParam> = vec![];
    while input.pos < 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 => {
                // capacity
                let code = input.read_8b()?;
                let len = input.read_8b()?;
                let value = input.read_n_bytes(len as usize)?;

                ParamValue::Capability(
                    Capability{
                        code,
                        len,
                        value,
                        capability_type: None
                    }
                )
            }
            _ => {
                // 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 DataBytes, 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![])
    }

    let prefixes = input.parse_nlri_list(add_path, afi, length)?;

    Ok(prefixes)
}

/// read bgp update message.
pub fn parse_bgp_update_message(input: &mut DataBytes, 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_16b()? as u64;
    let withdrawn_prefixes = read_nlri(input, withdrawn_length as usize, &afi, add_path)?;

    // parse attributes
    let attribute_length = input.read_16b()? as usize;
    let attr_parser = AttributeParser::new(add_path);

    let attributes = attr_parser.parse_attributes(input, asn_len, None, None, None, attribute_length)?;

    // 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
        }
    )
}