Request
The payload of the channel request: the tag byte 5 and the request of the channel.
[5]- No parameter. The channel request carries nothing after the tag.
The channel request is defined by diverge-sdk-rs/src/container_proxy/outside/endpoints/agents/begin/server/channel_request/frame.rs:
//! What a server's channel request frame carries for an agent
//! container begin.
use std::fmt;
use crate::wire::decode::Decode;
use crate::wire::encode::{Encode, Writer};
use crate::shared::containers::postgres;
use crate::shared::mcp;
/// What the proxy asks the server 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` | [`McpListTools`](Self::McpListTools) |
/// | `2` | [`McpListResources`](Self::McpListResources) |
/// | `3` | [`McpCallTool`](Self::McpCallTool) |
/// | `4` | [`McpReadResource`](Self::McpReadResource) |
/// | `5` | [`McpNotifications`](Self::McpNotifications) |
///
/// Six: everything an agent container asks of the world outside —
/// its database connections, its tool calls outward to the caller's
/// MCP servers — which the server relays to the caller as the
/// provider protocol's own channel requests. No daemon connection:
/// an agent container holds no account and asks the daemon nothing;
/// a tool container's begin has that ask and no tool call outward.
/// 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),
/// What tools the caller's servers have. Tag `1`.
///
/// The container asking OUTWARD: an agent's tool calls go to
/// servers that live with the caller, so the five exchanges in
/// [`shared::mcp`](crate::shared::mcp) travel this direction too.
McpListTools(mcp::list_tools::request::Request),
/// What resources they have. Tag `2`.
McpListResources(mcp::list_resources::request::Request),
/// Run one of their tools. Tag `3`.
McpCallTool(mcp::call_tool::request::Request),
/// Read one of their resources. Tag `4`.
McpReadResource(mcp::read_resource::request::Request),
/// Everything they say on their own account. Tag `5`.
McpNotifications(mcp::notifications::request::Request),
}
/// Tag for [`Frame::Postgres`].
const POSTGRES: u8 = 0;
/// Tag for [`Frame::McpListTools`].
const MCP_LIST_TOOLS: u8 = 1;
/// Tag for [`Frame::McpListResources`].
const MCP_LIST_RESOURCES: u8 = 2;
/// Tag for [`Frame::McpCallTool`].
const MCP_CALL_TOOL: u8 = 3;
/// Tag for [`Frame::McpReadResource`].
const MCP_READ_RESOURCE: u8 = 4;
/// Tag for [`Frame::McpNotifications`].
const MCP_NOTIFICATIONS: u8 = 5;
impl Encode for Frame {
/// The JSON failure from the asks that are JSON; everything else
/// is bytes copied.
type Error = FrameEncodeError;
fn encode(&self, out: &mut Writer<'_>) -> Result<(), FrameEncodeError> {
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::McpListTools(request) => {
out.extend_from_slice(&[MCP_LIST_TOOLS]);
request.encode(out).map_err(FrameEncodeError::Json)
}
Frame::McpListResources(request) => {
out.extend_from_slice(&[MCP_LIST_RESOURCES]);
request.encode(out).map_err(FrameEncodeError::Json)
}
Frame::McpCallTool(request) => {
out.extend_from_slice(&[MCP_CALL_TOOL]);
request.encode(out).map_err(FrameEncodeError::Json)
}
Frame::McpReadResource(request) => {
out.extend_from_slice(&[MCP_READ_RESOURCE]);
request.encode(out).map_err(FrameEncodeError::Json)
}
Frame::McpNotifications(request) => {
out.extend_from_slice(&[MCP_NOTIFICATIONS]);
request.encode(out).map_err(|error| match error {})
}
}
}
}
/// A agents begin channel request that could not be written.
#[derive(Debug)]
pub enum FrameEncodeError {
/// A JSON ask did not serialize.
Json(serde_json::Error),
}
impl fmt::Display for FrameEncodeError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
FrameEncodeError::Json(error) => {
write!(f, "channel request did not serialize: {error}")
}
}
}
}
impl std::error::Error for FrameEncodeError {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
match self {
FrameEncodeError::Json(error) => Some(error),
}
}
}
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),
MCP_LIST_TOOLS => mcp::list_tools::request::Request::decode(rest)
.map(Frame::McpListTools)
.map_err(FrameError::McpParams),
MCP_LIST_RESOURCES => {
mcp::list_resources::request::Request::decode(rest)
.map(Frame::McpListResources)
.map_err(FrameError::McpParams)
}
MCP_CALL_TOOL => mcp::call_tool::request::Request::decode(rest)
.map(Frame::McpCallTool)
.map_err(FrameError::McpParams),
MCP_READ_RESOURCE => {
mcp::read_resource::request::Request::decode(rest)
.map(Frame::McpReadResource)
.map_err(FrameError::McpParams)
}
MCP_NOTIFICATIONS => Ok(Frame::McpNotifications(
mcp::notifications::request::Request::decode(rest)
.unwrap_or_else(|error| match error {}),
)),
tag => Err(FrameError::UnknownTag(tag)),
}
}
}
/// A 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 six.
UnknownTag(u8),
/// The connection id was not four bytes.
Postgres(postgres::request::PostgresError),
/// One of the five MCP exchanges' params did not parse.
///
/// One variant for five tags, because they fail the same way and
/// the tag already said which was meant.
McpParams(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::McpParams(error) => {
write!(f, "mcp request params did not parse: {error}")
}
}
}
}
impl std::error::Error for FrameError {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
match self {
FrameError::McpParams(error) => Some(error),
FrameError::Postgres(error) => Some(error),
FrameError::Empty | FrameError::UnknownTag(_) => None,
}
}
}and by diverge-sdk-rs/src/shared/mcp/notifications/request/request.rs:
//! Asking to hear what a server says.
use std::convert::Infallible;
use crate::wire::decode::Decode;
use crate::wire::encode::{Encode, Writer};
/// Open the notification stream.
///
/// It carries nothing, and MCP is the reason rather than an economy.
/// Every other exchange here is a JSON-RPC method, and a request naming
/// one carries its params. This is not a method: in Streamable HTTP a
/// client opens the notification stream with a bare `GET` on the same
/// url it POSTs everything else to — no method name, no body, nothing
/// to say. There is no `notifications/subscribe` to mirror.
///
/// So the empty payload is the request, whole.
///
/// # It exists anyway
///
/// Rather than the channel request simply carrying no payload for this
/// one case. A frame that names five things should name them the same
/// way, and a variant with nothing in it is a variant a reader has to
/// check twice — once for what it means, once for why it is shaped
/// differently.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
pub struct Request;
/// Nothing at all. Which channel it arrives on says what it is, and
/// there is nothing else to say.
impl Encode for Request {
/// [`Infallible`]: no bytes.
type Error = Infallible;
fn encode(&self, _out: &mut Writer<'_>) -> Result<(), Infallible> {
Ok(())
}
}
impl Decode<'_> for Request {
/// [`Infallible`]: nothing is read, so nothing can be wrong.
type Error = Infallible;
/// Whatever bytes are there are ignored rather than rejected. There
/// is nothing this could carry, so a reader that found something
/// has met a writer from a version that gave it one — and the
/// channel already said what was meant.
fn decode(_bytes: &[u8]) -> Result<Self, Infallible> {
Ok(Request)
}
}