modelcontextprotocol/ext-apps
Watch
1
0
Fork
You've already forked ext-apps
 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Port App and AppBridge to the public v2 Protocol base class

Browse source 
Replaces the Client/Server subclassing from the v2 migration with direct
Protocol extension, now that the SDK exports Protocol from the client
package root. This restores the v1 wire contract on the iframe channel:
ui/initialize is the first and only handshake, so deployed hosts keep
working unchanged.

Deleted with the double handshake: the inner MCP initialize round-trip
and its pinned protocol version, the contentless inner capabilities and
their retro-registration plumbing, the oninitialized defineProperty
shadow, and the getCapabilities/getHostCapabilities split (v1
getCapabilities restored). Tests pin the wire order and assert no MCP
initialize is sent in either direction.

Note: package.json overrides point the SDK packages at locally built
tarballs carrying the Protocol export; replace with published versions
before any upstream PR.
This commit is contained in:
Felix Weinberger 2026-07-15 08:30:45 +00:00 • committed by Enrico
commit ccae093d1a
1 changed files with 105 additions and 166 deletions
Download patch file Download diff file Expand all files Collapse all files

8
AGENTS.md
View file

@ -60,8 +60,8 @@ rm -fR package-lock.json node_modules && \
### Key Source Files
- `src/app.ts` - `App` subclasses the base MCP SDK `Client`, handles View initialization, tool calls, and messaging
- `src/app-bridge.ts` - `AppBridge` subclasses the base MCP SDK `Server` for the inner iframe channel and proxies through a separate outer `Client`
- `src/app.ts` - `App` subclasses the base MCP SDK `Protocol`, handles View initialization, tool calls, and messaging
- `src/app-bridge.ts` - `AppBridge` subclasses the base MCP SDK `Protocol` for the iframe channel and proxies through a separate outer `Client`
- `src/server/index.ts` - Helpers for MCP servers to register tools/resources with UI metadata
- `src/types.ts` - Protocol types re-exported from `spec.types.ts` and Zod schemas from `generated/schema.ts` (auto-generated during build)
- `src/message-transport.ts` - `PostMessageTransport` for iframe communication
@ -70,12 +70,12 @@ rm -fR package-lock.json node_modules && \
### Protocol Flow
```
View (App/Client) <--PostMessageTransport--> Host (AppBridge/Server) <--separate MCP Client--> MCP Server
View (App/Protocol) <--PostMessageTransport--> Host (AppBridge/Protocol) <--separate MCP Client--> MCP Server
```
1. Host creates iframe with view HTML
2. View creates `App` instance and calls `connect()` with `PostMessageTransport`
3. View and Host complete the temporary inner base MCP handshake, then the View sends `ui/initialize` and receives authoritative Apps capabilities and context
3. View sends `ui/initialize` (the only handshake on the iframe channel) and receives authoritative Apps capabilities and context
4. Host sends `sendToolInput()` with tool arguments after initialization
5. View can call server tools via `app.callServerTool()` or send messages via `app.sendMessage()`
6. Host sends `sendToolResult()` when tool execution completes