Request
The payload of the channel request: the tag byte 1 and the request of the channel.
[1][params JSON …]- The params. The params of the MCP method
tools/list, as JSON, as the program sent them. _meta. The server sets nothing under_meta. Every member of_meta, and every other member of the params, is sent as the program sent it.
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/list_tools/request/request.rs:
//! Asking what tools there are.
use rmcp::model::{PaginatedRequestParams};
use serde_json::Error;
use crate::wire::decode::Decode;
use crate::wire::encode::{Encode, Writer};
/// Where in the listing to start, if anywhere in particular.
///
/// [`None`] asks for the first page, and is also what a caller with
/// nothing to say sends. It is optional because
/// [`rmcp`](rmcp::model::ListToolsRequest) makes it optional: params
/// absent and a cursor absent are different things to a server that
/// reads them.
///
/// # It is a wrapper, and a thin one
///
/// [`rmcp`] already defines the shape and this crate has no business
/// redefining it — an MCP request has one form and it is MCP's. What
/// the wrapper adds is the two impls beneath it, so that a channel
/// request carrying one writes `request.encode(out)` like every other
/// payload in this crate rather than reaching for `serde_json` itself.
#[derive(Debug, Clone, PartialEq, Default)]
pub struct Request(
/// The parameters, as [`rmcp`] defines them.
pub Option<PaginatedRequestParams>,
);
/// Its JSON, and nothing in front of it. The tag that says which
/// request this is belongs to whichever frame carries it.
impl Encode for Request {
/// The ordinary JSON failure.
type Error = Error;
fn encode(&self, out: &mut Writer<'_>) -> Result<(), Error> {
serde_json::to_writer(out, &self.0)
}
}
impl Decode<'_> for Request {
/// The ordinary JSON failure. There is nothing else here to get
/// wrong — no tag to be unknown, and no empty case, since no bytes
/// at all is a JSON document that ended too early and is reported
/// as one.
type Error = Error;
fn decode(bytes: &[u8]) -> Result<Self, Error> {
serde_json::from_slice(bytes).map(Request)
}
}