# ping.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/h2-0.3.2/src/frame/ping.rs`.
Keywords: rust, rustlang, rust-lang

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    use crate::frame::{Error, Frame, Head, Kind, StreamId};
    use bytes::BufMut;

    const ACK_FLAG: u8 = 0x1;

    pub type Payload = [u8; 8];

    #[derive(Debug, Eq, PartialEq)]
    pub struct Ping {
        ack: bool,
        payload: Payload,
    }

    // This was just 8 randomly generated bytes. We use something besides just
    // zeroes to distinguish this specific PING from any other.
    const SHUTDOWN_PAYLOAD: Payload = [0x0b, 0x7b, 0xa2, 0xf0, 0x8b, 0x9b, 0xfe, 0x54];
    const USER_PAYLOAD: Payload = [0x3b, 0x7c, 0xdb, 0x7a, 0x0b, 0x87, 0x16, 0xb4];

    impl Ping {
        #[cfg(feature = "unstable")]
        pub const SHUTDOWN: Payload = SHUTDOWN_PAYLOAD;

        #[cfg(not(feature = "unstable"))]
        pub(crate) const SHUTDOWN: Payload = SHUTDOWN_PAYLOAD;

        #[cfg(feature = "unstable")]
        pub const USER: Payload = USER_PAYLOAD;

        #[cfg(not(feature = "unstable"))]
        pub(crate) const USER: Payload = USER_PAYLOAD;

        pub fn new(payload: Payload) -> Ping {
            Ping {
                ack: false,
                payload,
            }
        }

        pub fn pong(payload: Payload) -> Ping {
            Ping { ack: true, payload }
        }

        pub fn is_ack(&self) -> bool {
            self.ack
        }

        pub fn payload(&self) -> &Payload {
            &self.payload
        }

        pub fn into_payload(self) -> Payload {
            self.payload
        }

        /// Builds a `Ping` frame from a raw frame.
        pub fn load(head: Head, bytes: &[u8]) -> Result<Ping, Error> {
            debug_assert_eq!(head.kind(), crate::frame::Kind::Ping);

            // PING frames are not associated with any individual stream. If a PING
            // frame is received with a stream identifier field value other than
            // 0x0, the recipient MUST respond with a connection error
            // (Section 5.4.1) of type PROTOCOL_ERROR.
            if !head.stream_id().is_zero() {
                return Err(Error::InvalidStreamId);
            }

            // In addition to the frame header, PING frames MUST contain 8 octets of opaque
            // data in the payload.
            if bytes.len() != 8 {
                return Err(Error::BadFrameSize);
            }

            let mut payload = [0; 8];
            payload.copy_from_slice(bytes);

            // The PING frame defines the following flags:
            //
            // ACK (0x1): When set, bit 0 indicates that this PING frame is a PING
            //    response. An endpoint MUST set this flag in PING responses. An
            //    endpoint MUST NOT respond to PING frames containing this flag.
            let ack = head.flag() & ACK_FLAG != 0;

            Ok(Ping { ack, payload })
        }

        pub fn encode<B: BufMut>(&self, dst: &mut B) {
            let sz = self.payload.len();
            tracing::trace!("encoding PING; ack={} len={}", self.ack, sz);

            let flags = if self.ack { ACK_FLAG } else { 0 };
            let head = Head::new(Kind::Ping, flags, StreamId::zero());

            head.encode(sz, dst);
            dst.put_slice(&self.payload);
        }
    }

    impl<T> From<Ping> for Frame<T> {
        fn from(src: Ping) -> Frame<T> {
            Frame::Ping(src)
        }
    }