Request
The payload of the channel request: the tag byte 0 and the request of the channel.
[0][connection_id: u32, big-endian]connection_id. Four bytes, big-endian, the id of the connection.
The channel request is defined by diverge-sdk-rs/src/container_proxy/outside/endpoints/tools/begin/server/channel_request/frame.rs:
//! What a server's channel request frame carries for a tool
//! container begin.
use std::convert::Infallible;
use std::fmt;
use crate::wire::decode::Decode;
use crate::wire::encode::{Encode, Writer};
use crate::shared::containers::{daemon, postgres};
/// What the proxy asks the server for once a tool container
/// has begun.
///
/// A payload leads with one byte saying which, and the rest is that
/// variant's own bytes.
///
/// | tag | asks for |
/// |-----|----------|
/// | `0` | [`Postgres`](Self::Postgres) |
/// | `1` | [`Daemon`](Self::Daemon) |
///
/// Two: everything a tool container asks of the world outside — its
/// database connections, its daemon connection — which the server
/// relays to the caller as the provider protocol's own channel
/// requests. No tool call outward: a tool container makes none, and
/// a proxy serving one answers its program's MCP client with an
/// error; an agent container's begin has those asks and no daemon
/// connection. The fuse asks are not here; each rides the scope of
/// the mount it belongs to.
#[derive(Debug, Clone, PartialEq)]
pub enum Frame {
/// The proxy's half of a database connection the container's
/// driver opened. Tag `0`.
///
/// An id the proxy minted. What comes back is everything the
/// database says; the server opens the other half, or declines by
/// finishing this one with nothing before it. See
/// [`postgres`](crate::shared::containers::postgres).
Postgres(postgres::request::Postgres),
/// A daemon connection the program opened, by the id the proxy
/// minted. Tag `1`.
///
/// This half is the proxy's own. What comes back on it is
/// everything the DAEMON says, as
/// [`daemon::server::Frame`](crate::shared::containers::daemon::server::Frame)s;
/// its finish is the connection closed, and an empty finish is the
/// connection declined. See
/// [`daemon`](crate::shared::containers::daemon) for the pair.
Daemon(daemon::request::Daemon),
}
/// Tag for [`Frame::Postgres`].
const POSTGRES: u8 = 0;
/// Tag for [`Frame::Daemon`].
const DAEMON: u8 = 1;
impl Encode for Frame {
/// [`Infallible`]: both asks are an id, bytes copied.
type Error = Infallible;
fn encode(&self, out: &mut Writer<'_>) -> Result<(), Infallible> {
match self {
Frame::Postgres(request) => {
out.extend_from_slice(&[POSTGRES]);
request.encode(out)
}
Frame::Daemon(request) => {
out.extend_from_slice(&[DAEMON]);
request.encode(out)
}
}
}
}
impl Decode<'_> for Frame {
/// Four ways to fail, and each names which ask it was.
type Error = FrameError;
fn decode(bytes: &[u8]) -> Result<Self, Self::Error> {
let (tag, rest) = bytes.split_first().ok_or(FrameError::Empty)?;
match *tag {
POSTGRES => postgres::request::Postgres::decode(rest)
.map(Frame::Postgres)
.map_err(FrameError::Postgres),
DAEMON => daemon::request::Daemon::decode(rest)
.map(Frame::Daemon)
.map_err(FrameError::Daemon),
tag => Err(FrameError::UnknownTag(tag)),
}
}
}
/// A tools begin channel request that could not be read.
#[derive(Debug)]
pub enum FrameError {
/// No bytes at all, so not even a tag.
Empty,
/// A tag that is none of this frame's two.
UnknownTag(u8),
/// The connection id was not four bytes.
Postgres(postgres::request::PostgresError),
/// The daemon connection's id was not four bytes.
Daemon(daemon::request::DaemonError),
}
impl fmt::Display for FrameError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
FrameError::Empty => {
f.write_str("tools begin channel request frame is empty")
}
FrameError::UnknownTag(tag) => {
write!(f, "unknown tools begin channel request tag {tag}")
}
FrameError::Postgres(error) => write!(f, "{error}"),
FrameError::Daemon(error) => write!(f, "{error}"),
}
}
}
impl std::error::Error for FrameError {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
match self {
FrameError::Daemon(error) => Some(error),
FrameError::Postgres(error) => Some(error),
FrameError::Empty | FrameError::UnknownTag(_) => None,
}
}
}and by diverge-sdk-rs/src/shared/containers/postgres/request/postgres.rs:
//! Naming a connection.
use std::error::Error;
use std::fmt;
use crate::wire::decode::Decode;
use crate::wire::encode::{Encode, Writer};
/// Which connection a channel is one half of.
///
/// The provider opens its half carrying this with an id it minted,
/// and the caller opens the other half quoting the same id. That is
/// the whole of the correlation: a caller with several connections in
/// flight learns which one it is being asked to feed.
///
/// # It is the provider's to choose and the provider's to keep unique
///
/// Unique among the connections this provider has open in this scope
/// — reusing one that is still live makes two connections
/// indistinguishable, and the provider is the only party that could
/// have prevented it. A number that counts up is the obvious way and
/// nothing requires it. Reusing one after both channels have finished
/// is fine; nothing here remembers.
///
/// # Why not the channel it arrived on
///
/// Because channels are numbered per SENDER. The provider opens its
/// half on a channel of its own, the caller opens the other on a
/// channel of its own, and neither side's header can name the other's
/// — so a payload quoting a channel number would be quoting one out of
/// a namespace its reader does not share. An id invented for the
/// connection belongs to neither channel, which is what makes it
/// readable on both sides — the same argument a
/// [`write_id`](crate::shared::containers::write_path::request::Request::write_id)
/// makes.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
pub struct Postgres {
/// What this connection is called, chosen by the provider.
pub connection_id: u32,
}
/// The bytes a connection id occupies.
const CONNECTION_ID_LEN: usize = 4;
/// Four big-endian bytes. No serialization, because a fixed-width
/// integer does not need one.
impl Encode for Postgres {
/// [`Infallible`](std::convert::Infallible): four known bytes.
type Error = std::convert::Infallible;
fn encode(&self, out: &mut Writer<'_>) -> Result<(), Self::Error> {
out.extend_from_slice(&self.connection_id.to_be_bytes());
Ok(())
}
}
impl Decode<'_> for Postgres {
/// One way to fail: the wrong number of bytes.
type Error = PostgresError;
fn decode(bytes: &[u8]) -> Result<Self, Self::Error> {
<[u8; CONNECTION_ID_LEN]>::try_from(bytes)
.map(|bytes| Postgres {
connection_id: u32::from_be_bytes(bytes),
})
.map_err(|_| PostgresError::Length(bytes.len()))
}
}
/// A Postgres channel request that could not be read.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum PostgresError {
/// A payload that was not four bytes, carrying however many there
/// were.
Length(usize),
}
impl fmt::Display for PostgresError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
PostgresError::Length(len) => {
write!(f, "postgres connection request is {len} bytes, not 4")
}
}
}
}
impl Error for PostgresError {}