Response

The sequence of channel responses the client answers with, what ends it, what a finish with nothing before it means, and what the server does with the answer.

• The sequence. Exactly one channel response, in the form the proxy’s /fuse/stat/{channel} page defines, followed by the channel response finish.
• A finish with nothing. A channel response finish that no channel response precedes states that the client did not serve the ask. The server relays that to the proxy as the ask not served, and does not ask again.

The channel response is defined by diverge-provider-sdk/src/shared/containers/fuse/stat/response/frame.rs:

//! The answer to a stat.

use std::convert::Infallible;

use super::super::super::ResponseError;
use super::super::Stat;
use crate::encode::{Encode, Writer};

/// The one message that answers a stat.
///
/// ```text
/// [kind: u8][stat… | message…]
/// ```
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Frame<'a> {
    /// Kind `0`. What the entry is and how long: a [`Stat`].
    Present(Stat),
    /// Kind `1`. There is nothing at the path. On a file mount, the
    /// caller holds nothing under the id yet, and the file reads as
    /// empty — the same absence [`read`](super::super::super::read)
    /// reports.
    Missing,
    /// Kind `2`. The stat was refused or failed, and this says why,
    /// for a reader rather than a program.
    Error(&'a str),
}

impl Encode for Frame<'_> {
    /// [`Infallible`]: a kind byte and fixed bytes, or a message
    /// copied.
    type Error = Infallible;

    fn encode(&self, out: &mut Writer<'_>) -> Result<(), Infallible> {
        match self {
            Frame::Present(stat) => {
                out.extend_from_slice(&[0]);
                stat.encode(out);
            }
            Frame::Missing => out.extend_from_slice(&[1]),
            Frame::Error(message) => {
                out.extend_from_slice(&[2]);
                out.extend_from_slice(message.as_bytes());
            }
        }
        Ok(())
    }
}

impl<'a> Frame<'a> {
    /// Decode the one message. The message borrows from `bytes`.
    pub fn decode(bytes: &'a [u8]) -> Result<Self, ResponseError> {
        let (kind, rest) = bytes.split_first().ok_or(ResponseError::Empty)?;
        match *kind {
            0 => Stat::decode(rest).map(|(stat, _)| Frame::Present(stat)),
            1 => Ok(Frame::Missing),
            2 => std::str::from_utf8(rest)
                .map(Frame::Error)
                .map_err(|_| ResponseError::MessageUtf8),
            other => Err(ResponseError::UnknownKind(other)),
        }
    }
}