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## Motivation and Context SEP-1865 "MCP Apps - Interactive User Interfaces for MCP" is Final on the Extensions Track: (https://github.com/modelcontextprotocol/modelcontextprotocol/pull/1865) an optional extension, negotiated through the SEP-2133 `capabilities.extensions` mechanism, that lets a server ship HTML user interfaces which the host renders for tool results. The normative spec lives in the ext-apps repository (`specification/2026-01-26/apps.mdx`). The Python SDK implements it in-SDK (python-sdk#3003, the `Apps` extension); the TypeScript ecosystem ships it as the separate `@modelcontextprotocol/ext-apps` package on top of the core SDK's SEP-2133 support. Server-side support is a thin convention layer over primitives this SDK already has (SEP-2133 extension capabilities, `_meta` on tools and resources, free-form resource URIs and MIME types). New `MCP::Apps` module: - Wire vocabulary constants shared with the reference implementations: `EXTENSION_ID` (`"io.modelcontextprotocol/ui"` - note `/ui`, not `/apps`), `RESOURCE_MIME_TYPE` (`"text/html;profile=mcp-app"`), `URI_SCHEME` (`"ui://"`), and the legacy flat meta key `RESOURCE_URI_META_KEY` (`"ui/resourceUri"`). - `Apps.capability(mime_types:)` builds the `capabilities.extensions` fragment for `support_extensions` on the server or `connect` on the client. - `Apps.ui_resource(uri:, name:, ...)` builds an `MCP::Resource` for a UI template, enforcing the spec's MUSTs (a `ui://` URI; the parameterized HTML MIME type by default). - `Apps.tool_meta(resource_uri:, visibility:, meta:, legacy:)` builds the `_meta.ui.resourceUri` linkage (optionally also emitting the legacy flat alias, matching the reference server helper that keeps both shapes in sync), merged non-destructively into caller-supplied meta. - `Apps.client_supports?(client_capabilities, mime_type:)` gates the text-only fallback the extension requires for clients that did not declare the capability (symbol/string tolerant). Everything else the extension defines (the sandboxed iframe, the `ui/*` postMessage bridge methods, consent for UI-initiated calls) is HOST responsibility and out of scope for a server SDK; a server only ever receives ordinary `resources/read` and `tools/call` requests. The README section states this boundary. Resolves #376. ## How Has This Been Tested? New `test/mcp/apps_test.rb` pins the wire vocabulary and covers the capability fragment, `ui_resource` scheme validation and MIME default, `tool_meta` non-destructive merging, visibility, the legacy alias, and `client_supports?` across symbol/string keys, mimeTypes narrowing, and missing declarations. New integration tests in `test/mcp/server_test.rb` drive a full server: the `initialize` result advertises the extension, tools/list serializes `_meta.ui.resourceUri`, `resources/read` serves the HTML template, and `client_supports?` distinguishes hosts with and without the declared extension. `bundle exec rake` (tests, RuboCop, and conformance baseline) passes. Also verified end-to-end over stdio: a client connecting with the extension declared negotiates the capability, discovers the tool linkage via `_meta.ui.resourceUri`, and reads the `ui://` template as `text/html;profile=mcp-app` content. ## Breaking Changes None. Purely additive helper module; no existing code paths change.
34 lines
914 B
Ruby
34 lines
914 B
Ruby
# frozen_string_literal: true
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require_relative "json_rpc_handler"
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require_relative "mcp/configuration"
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require_relative "mcp/string_utils"
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require_relative "mcp/transport"
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require_relative "mcp/version"
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module MCP
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autoload :Annotations, "mcp/annotations"
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autoload :Apps, "mcp/apps"
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autoload :Cancellation, "mcp/cancellation"
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autoload :CancelledError, "mcp/cancelled_error"
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autoload :Client, "mcp/client"
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autoload :Content, "mcp/content"
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autoload :Icon, "mcp/icon"
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autoload :Prompt, "mcp/prompt"
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autoload :Resource, "mcp/resource"
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autoload :ResourceTemplate, "mcp/resource_template"
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autoload :Server, "mcp/server"
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autoload :ServerSession, "mcp/server_session"
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autoload :Tool, "mcp/tool"
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autoload :TraceContext, "mcp/trace_context"
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class << self
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def configure
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yield(configuration)
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end
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def configuration
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@configuration ||= Configuration.new
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end
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end
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end
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