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use std::io;

pub struct RtpReader<'a> {
    buf: &'a [u8],
}

fn other(s: &str) -> io::Error {
    io::Error::new(io::ErrorKind::Other, s)
}

impl<'a> RtpReader<'a> {
    pub fn new(b: &'a [u8]) -> io::Result<RtpReader> {
        if b.len() <= 12 {
            return Err(other("Buffer too short to be valid RTP packet"));
        }
        let r = RtpReader{ buf: b };
        if r.version() != 2 {
            return Err(other("Only RTP version 2 supported"));
        }
        if r.payload_offset() > b.len() {
            return Err(other("RTP headers truncated before end of buffer"));
        }
        Ok(r)
    }

    pub fn version(&self) -> u8 {
        (self.buf[0] & 0b11000000) >> 6
    }
    pub fn padding(&self) -> bool {
        (self.buf[0] & 0b00100000) != 0
    }
    pub fn extension(&self) -> bool {
        (self.buf[0] & 0b00010000) != 0
    }
    pub fn csrc_count(&self) -> u8 {
        self.buf[0] & 0b00001111
    }
    pub fn mark(&self) -> bool {
        (self.buf[1] & 0b10000000) != 0
    }
    pub fn payload_type(&self) -> u8 {
        self.buf[1] & 0b01111111
    }
    pub fn sequence_number(&self) -> u16 {
        (self.buf[2] as u16) << 8 | (self.buf[3] as u16)
    }
    pub fn timestamp(&self) -> u32 {
        (self.buf[4] as u32) << 24 | (self.buf[5] as u32) << 16 | (self.buf[6] as u32) << 8 | (self.buf[7] as u32)
    }
    pub fn ssrc(&self) -> u32 {
        (self.buf[8] as u32) << 24 | (self.buf[9] as u32) << 16 | (self.buf[10] as u32) << 8 | (self.buf[11] as u32)
    }

    fn payload_offset(&self) -> usize {
        let offset = 12 + (4 * self.csrc_count()) as usize;
        if self.extension() {
            let len = (self.buf[offset+2] as usize) << 8 | (self.buf[offset+3] as usize);
            offset + 4 + len
        } else {
            offset
        }
    }

    pub fn payload(&self) -> &'a[u8] {
        &self.buf[self.payload_offset()..]
    }
}


#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn version() {
        let data = [
            0x80u8, 0xe0u8, 0x27u8, 0x38u8, 0x64u8, 0xe4u8, 0x05u8, 0xa7u8, 0xa2u8, 0x42u8, 0xafu8,
            0x01u8, 0x3cu8, 0x41u8, 0xa4u8, 0xa3u8, 0x5du8, 0x13u8, 0xf9u8, 0xcau8, 0x2cu8, 0x7eu8,
            0xa9u8, 0x77u8, 0xaau8, 0xdeu8, 0xf7u8, 0xcau8, 0xa4u8, 0x28u8, 0xfeu8, 0xdfu8, 0xc8u8,
            0x68u8, 0xf1u8, 0xd9u8, 0x4fu8, 0x69u8, 0x96u8, 0xa0u8, 0x57u8, 0xbau8, 0xfbu8, 0x07u8,
            0xc4u8, 0xc4u8, 0xd4u8, 0xfeu8, 0xf8u8, 0xc7u8, 0xb2u8, 0x0du8, 0x01u8, 0x12u8, 0x14u8,
            0x36u8, 0x69u8, 0x75u8, 0xf2u8, 0xb4u8, 0xb5u8, 0xf2u8, 0x54u8, 0x2eu8, 0xc2u8, 0x66u8,
            0x51u8, 0xebu8, 0x41u8, 0x80u8, 0x96u8, 0xceu8, 0x8eu8, 0x60u8, 0xb2u8, 0x44u8, 0xaeu8,
            0xe5u8, 0x43u8, 0xadu8, 0x7bu8, 0x48u8, 0x89u8, 0x44u8, 0xb0u8, 0x48u8, 0x67u8, 0x6au8,
            0x84u8, 0x7au8, 0x0au8, 0x8fu8, 0x71u8, 0x50u8, 0x69u8, 0xe6u8, 0xb1u8, 0x05u8, 0x40u8,
            0xb9u8, 0x8cu8, 0xafu8, 0x42u8, 0xcbu8, 0x58u8, 0x83u8, 0xcbu8, 0x32u8, 0x64u8, 0xd2u8,
            0x2au8, 0x7du8, 0x4eu8, 0xf5u8, 0xbcu8, 0x33u8, 0xfeu8, 0xb7u8, 0x0cu8, 0xe4u8, 0x8eu8,
            0x38u8, 0xbcu8, 0x3au8, 0x1eu8, 0xd2u8, 0x56u8, 0x13u8, 0x23u8, 0x47u8, 0xcfu8, 0x42u8,
            0xa9u8, 0xbbu8, 0xcfu8, 0x48u8, 0xf3u8, 0x11u8, 0xc7u8, 0xfdu8, 0x73u8, 0x2du8, 0xe1u8,
            0xeau8, 0x47u8, 0x5cu8, 0x5du8, 0x11u8, 0x96u8, 0x1eu8, 0xc4u8, 0x70u8, 0x32u8, 0x77u8,
            0xabu8, 0x31u8, 0x7au8, 0xb1u8, 0x22u8, 0x14u8, 0x8du8, 0x2bu8, 0xecu8, 0x3du8, 0x67u8,
            0x97u8, 0xa4u8, 0x40u8, 0x21u8, 0x1eu8, 0xceu8, 0xb0u8, 0x63u8, 0x01u8, 0x75u8, 0x77u8,
            0x03u8, 0x15u8, 0xcdu8, 0x35u8, 0xa1u8, 0x2fu8, 0x4bu8, 0xa0u8, 0xacu8, 0x8du8, 0xd7u8,
            0x78u8, 0x02u8, 0x23u8, 0xcbu8, 0xfdu8, 0x82u8, 0x4eu8, 0x0bu8, 0x79u8, 0x7fu8, 0x39u8,
            0x70u8, 0x26u8, 0x66u8, 0x37u8, 0xe9u8, 0x93u8, 0x91u8, 0x7bu8, 0xc4u8, 0x80u8, 0xa9u8,
            0x18u8, 0x23u8, 0xb3u8, 0xa1u8, 0x04u8, 0x72u8, 0x53u8, 0xa0u8, 0xb4u8, 0xffu8, 0x79u8,
            0x1fu8, 0x07u8, 0xe2u8, 0x5du8, 0x01u8, 0x7du8, 0x63u8, 0xc1u8, 0x16u8, 0x89u8, 0x23u8,
            0x4au8, 0x17u8, 0xbbu8, 0x6du8, 0x0du8, 0x81u8, 0x1au8, 0xbbu8, 0x94u8, 0x5bu8, 0xcbu8,
            0x2du8, 0xdeu8, 0x98u8, 0x40u8, 0x22u8, 0x62u8, 0x41u8, 0xc2u8, 0x9bu8, 0x95u8, 0x85u8,
            0x60u8, 0xf0u8, 0xdeu8, 0x6fu8, 0xeeu8, 0x93u8, 0xccu8, 0x15u8, 0x76u8, 0xfbu8, 0xf8u8,
            0x8au8, 0x1du8, 0xe1u8, 0x83u8, 0x12u8, 0xabu8, 0x25u8, 0x6au8, 0x7bu8, 0x89u8, 0xedu8,
            0x70u8, 0x4eu8, 0xcdu8, 0x1eu8, 0xa9u8, 0xfcu8, 0xa8u8, 0x22u8, 0x91u8, 0x5fu8, 0x50u8,
            0x68u8, 0x6au8, 0x35u8, 0xf7u8, 0xc1u8, 0x1eu8, 0x15u8, 0x37u8, 0xb4u8, 0x30u8, 0x62u8,
            0x56u8, 0x1eu8, 0x2eu8, 0xe0u8, 0x2du8, 0xa4u8, 0x1eu8, 0x75u8, 0x5bu8, 0xc7u8, 0xd0u8,
            0x5bu8, 0x9du8, 0xd0u8, 0x25u8, 0x76u8, 0xdfu8, 0xa7u8, 0x19u8, 0x12u8, 0x93u8, 0xf4u8,
            0xebu8, 0x02u8, 0xf2u8, 0x4au8, 0x13u8, 0xe9u8, 0x1cu8, 0x17u8, 0xccu8, 0x11u8, 0x87u8,
            0x9cu8, 0xa6u8, 0x40u8, 0x27u8, 0xb7u8, 0x2bu8, 0x9bu8, 0x6fu8, 0x23u8, 0x06u8, 0x2cu8,
            0xc6u8, 0x6eu8, 0xc1u8, 0x9au8, 0xbdu8, 0x59u8, 0x37u8, 0xe9u8, 0x9eu8, 0x76u8, 0xf6u8,
            0xc1u8, 0xbcu8, 0x81u8, 0x18u8, 0x60u8, 0xc9u8, 0x64u8, 0x0au8, 0xb3u8, 0x6eu8, 0xf3u8,
            0x6bu8, 0xb9u8, 0xd0u8, 0xf6u8, 0xe0u8, 0x9bu8, 0x91u8, 0xc1u8, 0x0fu8, 0x96u8, 0xefu8,
            0xbcu8, 0x5fu8, 0x8eu8, 0x86u8, 0x56u8, 0x5au8, 0xfcu8, 0x7au8, 0x8bu8, 0xddu8, 0x9au8,
            0x1cu8, 0xf6u8, 0xb4u8, 0x85u8, 0xf4u8, 0xb0u8, 
        ];
        let header = RtpReader { buf: &data };
        assert_eq!(2, header.version());
        assert!(!header.padding());
        assert!(!header.extension());
        assert_eq!(0, header.csrc_count());
        assert!(header.mark());
        assert_eq!(96, header.payload_type());
        assert_eq!(10040, header.sequence_number());
        assert_eq!(1692665255, header.timestamp());
        assert_eq!(0xa242af01, header.ssrc());
        assert_eq!(379, header.payload().len());
    }
}