path: root/src/protocol/gtpv1.rs

use crate::protocol::codec::Decode;
use nom::bits;
use nom::bytes;
use nom::error::Error;
use nom::number;
use nom::sequence;
use nom::IResult;

/******************************************************************************
 * Struct
 ******************************************************************************/

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct GTPv1Option {
    pub sequence_number: u16, // 16bit
    pub npdu_number: u8,      // 8bit
    pub next_header_type: u8, // 8bit
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct GTPv1ExtensionHeader {
    pub length: u8, // 8bit (单位4字节，包括长度/内容/下一扩展消息头字段)
    pub contents: Vec<u8>,
    pub next_header_type: u8, // 8bit
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct GTPv1Header {
    pub version: u8,               // 3bit 1: GTPv1
    pub protocol_type: u8,         // 1bit
    pub reserved: u8,              // 1bit
    pub extension_header_flag: u8, // 1bit
    pub sequence_number_flag: u8,  // 1bit
    pub npdu_number_flag: u8,      // 1bit

    pub message_type: u8,    // 8bit
    pub message_length: u16, // 16bit (单位为字节，不包括GTP头前8字节的必选字段)
    pub teid: u32,           // 32bit

    // extension_header_flag/sequence_number_flag/npdu_number_flag任意一个取值为1时options字段才存在
    pub options: Option<GTPv1Option>,
    pub extensions: Vec<GTPv1ExtensionHeader>,
}

/******************************************************************************
 * API
 ******************************************************************************/

fn bit_decode(input: &[u8]) -> IResult<&[u8], (u8, u8, u8, u8, u8, u8)> {
    bits::bits::<_, _, Error<_>, _, _>(sequence::tuple((
        bits::streaming::take(3u8),
        bits::streaming::take(1u8),
        bits::streaming::take(1u8),
        bits::streaming::take(1u8),
        bits::streaming::take(1u8),
        bits::streaming::take(1u8),
    )))(input)
}

fn option_decode(input: &[u8]) -> IResult<&[u8], GTPv1Option> {
    let (input, sequence_number) = number::streaming::be_u16(input)?;
    let (input, npdu_number) = number::streaming::be_u8(input)?;
    let (input, next_header_type) = number::streaming::be_u8(input)?;

    Ok((
        input,
        GTPv1Option {
            sequence_number,
            npdu_number,
            next_header_type,
        },
    ))
}

fn extension_decode(input: &[u8]) -> IResult<&[u8], GTPv1ExtensionHeader> {
    let (input, length) = number::streaming::be_u8(input)?;
    if length * 4 < 2 {
        return Err(nom::Err::Incomplete(nom::Needed::new(
            (2 - length * 4).into(),
        )));
    }
    let (input, contents) = bytes::streaming::take(length * 4 - 2)(input)?;
    let (input, next_header_type) = number::streaming::be_u8(input)?;
    Ok((
        input,
        GTPv1ExtensionHeader {
            length,
            contents: contents.to_vec(),
            next_header_type,
        },
    ))
}

impl Decode for GTPv1Header {
    type Iterm = GTPv1Header;
    fn decode(input: &[u8]) -> IResult<&[u8], GTPv1Header> {
        let (
            input,
            (
                version,
                protocol_type,
                reserved,
                extension_header_flag,
                sequence_number_flag,
                npdu_number_flag,
            ),
        ) = bit_decode(input)?;
        match (version, protocol_type) {
            (1, 1) => (),
            (_, _) => {
                return Err(nom::Err::Error(Error::new(
                    input,
                    nom::error::ErrorKind::TagBits,
                )))
            }
        }
        let (input, message_type) = number::streaming::be_u8(input)?;
        let (input, message_length) = number::streaming::be_u16(input)?;
        let (input, teid) = number::streaming::be_u32(input)?;

        // Optional word of GTP header, present if any of extension_header_flag, sequence_number_flag, npdu_number_flag is set
        let mut remain = input;
        let mut options = None;
        if extension_header_flag == 1 || sequence_number_flag == 1 || npdu_number_flag == 1 {
            let (left, _options) = option_decode(remain)?;
            remain = left;
            options = Some(_options);
        }

        let mut extensions = Vec::new();
        if options.is_some() {
            let mut next_header = options.clone().unwrap().next_header_type;
            while next_header != 0 {
                let (left, extension) = extension_decode(remain)?;
                remain = left;
                next_header = extension.next_header_type;
                extensions.push(extension);
            }
        }

        Ok((
            remain,
            GTPv1Header {
                version,
                protocol_type,
                reserved,
                extension_header_flag,
                sequence_number_flag,
                npdu_number_flag,
                message_type,
                message_length,
                teid,
                options,
                extensions,
            },
        ))
    }
}

/******************************************************************************
 * TEST
 ******************************************************************************/

#[cfg(test)]
mod tests {
    use super::GTPv1ExtensionHeader;
    use super::GTPv1Header;
    use crate::protocol::codec::Decode;
    const LAST_SLICE: &'static [u8] = &[0xff];

    #[test]
    fn gtpv1_header_decode() {
        /*
         * GPRS Tunneling Protocol
         *     Flags: 0x30
         *         001. .... = Version: GTP release 99 version (1)
         *         ...1 .... = Protocol type: GTP (1)
         *         .... 0... = Reserved: 0
         *         .... .0.. = Is Next Extension Header present?: No
         *         .... ..0. = Is Sequence Number present?: No
         *         .... ...0 = Is N-PDU number present?: No
         *     Message Type: T-PDU (0xff)
         *     Length: 64
         *     TEID: 0x1f54d4b5 (525653173)
         */

        let bytes = [
            0x30, 0xff, 0x00, 0x40, 0x1f, 0x54, 0xd4, 0xb5, 0xff, /* Payload */
        ];

        let expectation = GTPv1Header {
            version: 1,
            protocol_type: 1,
            reserved: 0,
            extension_header_flag: 0,
            sequence_number_flag: 0,
            npdu_number_flag: 0,
            message_type: 0xff,
            message_length: 64,
            teid: 525653173,
            options: None,
            extensions: vec![],
        };

        assert_eq!(GTPv1Header::decode(&bytes), Ok((LAST_SLICE, expectation)));

        // example
        let result = GTPv1Header::decode(&bytes);
        match result {
            Ok((payload, header)) => {
                println!("OK: {:?}, payload: {}", header, payload.len());
            }
            Err(e) => {
                println!("ERR: {:?}", e);
            }
        }

        // assert_eq!(1, 0);
    }

    #[test]
    fn gtpv1_extension_decode() {
        /*
         * GPRS Tunneling Protocol
         *     Flags: 0x36
         *         001. .... = Version: GTP release 99 version (1)
         *         ...1 .... = Protocol type: GTP (1)
         *         .... 0... = Reserved: 0
         *         .... .1.. = Is Next Extension Header present?: Yes
         *         .... ..1. = Is Sequence Number present?: Yes
         *         .... ...0 = Is N-PDU number present?: No
         *     Message Type: T-PDU (0xff)
         *     Length: 48
         *     TEID: 0x1c6596fc (476419836)
         *     Sequence number: 0x6739 (26425)
         *     Next extension header type: PDU Session container (0x85)
         *     Extension header (PDU Session container)
         *         Extension Header Length: 1
         *         PDU Session Container
         *             0001 .... = PDU Type: UL PDU SESSION INFORMATION (1)
         *             .... 0000 = Spare: 0x0
         *             00.. .... = Spare: 0x0
         *             ..00 0001 = QoS Flow Identifier (QFI): 1
         *         Next extension header type: No more extension headers (0x00)
         */

        let bytes = [
            0x36, 0xff, 0x00, 0x30, 0x1c, 0x65, 0x96, 0xfc, 0x67, 0x39, 0x00, 0x85, 0x01, 0x10,
            0x01, 0x00, 0xff, /* Payload */
        ];

        let expectation = GTPv1Header {
            version: 1,
            protocol_type: 1,
            reserved: 0,
            extension_header_flag: 1,
            sequence_number_flag: 1,
            npdu_number_flag: 0,
            message_type: 0xff,
            message_length: 48,
            teid: 476419836,
            options: Some(super::GTPv1Option {
                sequence_number: 26425,
                npdu_number: 0,
                next_header_type: 0x85,
            }),
            extensions: vec![GTPv1ExtensionHeader {
                length: 1,
                contents: vec![0x10, 0x01],
                next_header_type: 0x00,
            }],
        };

        assert_eq!(GTPv1Header::decode(&bytes), Ok((LAST_SLICE, expectation)));

        // example
        let result = GTPv1Header::decode(&bytes);
        match result {
            Ok((payload, header)) => {
                println!("OK: {:?}, payload: {}", header, payload.len());
            }
            Err(e) => {
                println!("ERR: {:?}", e);
            }
        }

        // assert_eq!(1, 0);
    }
}