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. The id the server announced on its own postgres channel, as four bytes, big-endian.- Malformed. A channel request whose payload does not decode as stated is answered by a channel response finish that no channel response precedes, and the server does nothing else for it.
The channel request is defined by diverge-sdk-rs/src/container_proxy/outside/endpoints/agents/begin/client/channel_request/frame.rs:
//! What a client's channel request frame carries for an agent
//! container begin.
use std::error::Error;
use std::fmt;
use crate::wire::decode::Decode;
use crate::wire::encode::{Encode, Writer};
use crate::shared::containers::secrets::Values;
use crate::shared::containers::{dequeue, enqueue, postgres};
/// What the server asks the proxy for once an agent 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` | [`Info`](Self::Info) |
/// | `2` | [`Enqueue`](Self::Enqueue) |
/// | `3` | [`Dequeue`](Self::Dequeue) |
/// | `4` | [`Secrets`](Self::Secrets) |
///
/// The first two are the same in both begin scopes, so a reader of
/// one is a reader of both; what follows is this family's own
/// exchange — no daemon connection among them, since an agent
/// container holds no account and asks the daemon nothing — and
/// then the feed, which both scopes have again under a tag of their
/// own. All of them reach INTO the container: the last hop of what a
/// caller opened on the provider, or of what the caller fed. What
/// comes OUT of the agent — its conversation — is no channel: it
/// rides the begin's own main stream.
#[derive(Debug, Clone, PartialEq)]
pub enum Frame {
/// The server's half of a database connection. Tag `0`.
///
/// Opened once the server has taken the proxy's half, quoting the
/// same connection; what comes back is everything the container's
/// driver wrote. See
/// [`postgres`](crate::shared::containers::postgres) for the pair.
Postgres(postgres::request::Postgres),
/// What the arguments may be. Tag `1`.
///
/// Carries nothing — the variant is bare — and the proxy answers
/// with the image's DIVERGE.md, parsed — read from the
/// container's root, the program never asked — or that it has
/// none. See [`info`](crate::shared::containers::info).
Info,
/// A message for the agent. Tag `2`.
///
/// The one way into it: a message with no loop running starts one,
/// on that message, and a message while one runs joins its queue.
/// Answered once — by an
/// [`enqueue::response::Frame`](crate::shared::containers::enqueue::response::Frame)
/// naming the message's fate, whenever that is known — and then the
/// finish. What the agent says in reply is the begin's main stream.
/// See [`enqueue`](crate::shared::containers::enqueue).
Enqueue(enqueue::request::Request),
/// Withdraw every message still waiting under a key. Tag `3`.
///
/// Carries the key, as the enqueues gave it. Answered once — by a
/// [`dequeue::response::Frame`](crate::shared::containers::dequeue::response::Frame)
/// saying whether anything waited under it — and then the finish.
/// Each message it withdraws is ALSO answered, on its own enqueue
/// channel. See [`dequeue`](crate::shared::containers::dequeue).
Dequeue(dequeue::request::Request),
/// The secrets' values, fed to the program. Tag `4`.
///
/// Carries the [`Values`] as JSON — every name the program
/// declared, each to its value — which the proxy hands the
/// program on `POST /secrets` and holds until that call answers.
/// Opened by the server once before it sends the run's id and
/// again at every activation, relaying the caller's own feed.
/// Answered once — by a
/// [`feed::response::Frame`](crate::shared::containers::secrets::feed::response::Frame),
/// `Fed` or the program's refusal — and then the finish; a `Fed`
/// opens the gate the proxy holds every delivery behind. See
/// [`secrets`](crate::shared::containers::secrets).
Secrets(Values),
}
/// Tag for [`Frame::Postgres`].
const POSTGRES: u8 = 0;
/// Tag for [`Frame::Info`].
const INFO: u8 = 1;
/// Tag for [`Frame::Enqueue`].
const ENQUEUE: u8 = 2;
/// Tag for [`Frame::Dequeue`].
const DEQUEUE: u8 = 3;
/// Tag for [`Frame::Secrets`].
const SECRETS: u8 = 4;
impl Encode for Frame {
/// The ordinary JSON failure, from whichever ask has one.
type Error = serde_json::Error;
fn encode(&self, out: &mut Writer<'_>) -> Result<(), Self::Error> {
match self {
Frame::Postgres(request) => {
out.extend_from_slice(&[POSTGRES]);
// Its error is `Infallible`, and an empty match on one
// is how you say so: there is no value to handle.
request.encode(out).map_err(|error| match error {})
}
Frame::Info => {
out.extend_from_slice(&[INFO]);
Ok(())
}
Frame::Enqueue(request) => {
out.extend_from_slice(&[ENQUEUE]);
request.encode(out)
}
Frame::Dequeue(request) => {
out.extend_from_slice(&[DEQUEUE]);
request.encode(out)
}
Frame::Secrets(values) => {
out.extend_from_slice(&[SECRETS]);
serde_json::to_writer(out, values)
}
}
}
}
impl Decode<'_> for Frame {
/// Several ways to fail, and the parses among them name which.
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),
INFO => Ok(Frame::Info),
ENQUEUE => enqueue::request::Request::decode(rest)
.map(Frame::Enqueue)
.map_err(FrameError::Enqueue),
DEQUEUE => dequeue::request::Request::decode(rest)
.map(Frame::Dequeue)
.map_err(FrameError::Dequeue),
SECRETS => serde_json::from_slice(rest)
.map(Frame::Secrets)
.map_err(FrameError::Secrets),
tag => Err(FrameError::UnknownTag(tag)),
}
}
}
/// An agents 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.
UnknownTag(u8),
/// The connection id was not four bytes.
Postgres(postgres::request::PostgresError),
/// The enqueued message did not parse as JSON.
Enqueue(serde_json::Error),
/// The dequeue's key did not parse as JSON.
Dequeue(serde_json::Error),
/// The secrets' values did not parse as JSON. The message is the
/// parser's, which quotes no value.
Secrets(serde_json::Error),
}
impl fmt::Display for FrameError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
FrameError::Empty => {
f.write_str("agents begin channel request frame is empty")
}
FrameError::UnknownTag(tag) => {
write!(f, "unknown agents begin channel request tag {tag}")
}
FrameError::Postgres(error) => write!(f, "{error}"),
FrameError::Enqueue(error) => {
write!(f, "enqueue request did not parse: {error}")
}
FrameError::Dequeue(error) => {
write!(f, "dequeue request did not parse: {error}")
}
FrameError::Secrets(error) => {
write!(f, "secrets feed did not parse: {error}")
}
}
}
}
impl Error for FrameError {
fn source(&self) -> Option<&(dyn Error + 'static)> {
match self {
FrameError::Enqueue(error) | FrameError::Dequeue(error) | FrameError::Secrets(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 {}