Class: ClaudeAgentSDK::SdkMcpServer

Inherits:
Object
  • Object
show all
Defined in:
lib/claude_agent_sdk/sdk_mcp_server.rb

Overview

SDK MCP Server - wraps official MCP::Server with block-based API

Unlike external MCP servers that run as separate processes, SDK MCP servers run directly in your application's process, providing better performance and simpler deployment.

This class wraps the official MCP Ruby SDK and provides a simpler block-based API for defining tools, resources, and prompts.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(name:, version: '1.0.0', tools: [], resources: [], prompts: []) ⇒ SdkMcpServer

Returns a new instance of SdkMcpServer.



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 106

def initialize(name:, version: '1.0.0', tools: [], resources: [], prompts: [])
  @name = name
  @version = version
  @tools = tools
  @resources = resources
  @prompts = prompts
  @callback_scheduling = :thread

  # Create dynamic Tool classes from tool definitions
  tool_classes = create_tool_classes(tools)

  # Resources are served as MCP::Resource instances; reads go through
  # the gem's registerable handler (see register_resources_read_handler).
  resource_instances = create_resource_instances(resources)

  # Create dynamic Prompt classes from prompt definitions
  prompt_classes = create_prompt_classes(prompts)

  # Create the official MCP::Server instance
  @mcp_server = MCP::Server.new(
    name: name,
    version: version,
    tools: tool_classes,
    resources: resource_instances,
    prompts: prompt_classes
  )
  register_resources_read_handler
end

Instance Attribute Details

#callback_scheduling ⇒ Object

Default for where user handlers run when this server is invoked DIRECTLY (call_tool / read_resource / get_prompt outside a session): :thread hops to a plain thread, :inline runs in place. When a session dispatches to this server, the session's own mode arrives via fiber storage instead (see #effective_callback_scheduling) — a server shared by concurrent sessions with different modes is never mutated, so modes cannot cross-contaminate or persist past a session.



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 91

def callback_scheduling
  @callback_scheduling
end

#mcp_server ⇒ Object (readonly)

Returns the value of attribute mcp_server.



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 82

def mcp_server
  @mcp_server
end

#name ⇒ Object (readonly)

Returns the value of attribute name.



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 82

def name
  @name
end

#prompts ⇒ Object (readonly)

Returns the value of attribute prompts.



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 82

def prompts
  @prompts
end

#resources ⇒ Object (readonly)

Returns the value of attribute resources.



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 82

def resources
  @resources
end

#tools ⇒ Object (readonly)

Returns the value of attribute tools.



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 82

def tools
  @tools
end

#version ⇒ Object (readonly)

Returns the value of attribute version.



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 82

def version
  @version
end

Instance Method Details

#call_tool(name, arguments) ⇒ Hash

Execute a tool by name (backward-compat public API; Query's tools/call dispatch routes through handle_message/the official MCP::Server, which also validates arguments against the tool's inputSchema — this direct path bypasses that validation). Tool-execution failures are reported in-band (isError: true) per the MCP spec and Python parity (the mcp lowlevel server converts handler exceptions to CallToolResult(isError=True)); they must NOT become JSON-RPC protocol errors — the model needs the error text to self-correct.

Parameters:

  • name (String) —

    Tool name

  • arguments (Hash) —

    Tool arguments

Returns:

  • (Hash) —

    Tool result (with isError: true on failure)



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 193

def call_tool(name, arguments)
  tool = @tools.find { |t| t.name == name }
  return error_tool_result("Tool '#{name}' not found") unless tool

  # Call the tool's handler on a plain thread (default) so the async
  # gem's Fiber scheduler is not visible to user code (which may hit
  # AR/PG); in :inline mode it runs in place on the reactor fiber.
  result = FiberBoundary.invoke(scheduling: effective_callback_scheduling) { tool.handler.call(arguments) }

  # Guard before flexible_fetch: it raises on non-Hash inputs.
  content = result.is_a?(Hash) ? ClaudeAgentSDK.flexible_fetch(result, "content", "content") : nil
  return error_tool_result("Tool '#{name}' must return a hash with :content key") unless content

  result
rescue StandardError => e
  # Bare e.message like Python's str(e) — no prefix.
  error_tool_result(e.message)
end

#effective_callback_scheduling ⇒ Object

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Internal — public only so the dynamic tool classes can reach it. The scheduling mode for the current invocation: the dispatching session's mode (a live SchedulingScope in fiber storage, set by Query around the dispatch) when present, else this server's own default. A scope inherited from an already-finished dispatch is closed and deliberately ignored — a child task spawned inside a handler must not carry the session mode into later direct calls.



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 101

def effective_callback_scheduling
  scope = Fiber[FiberBoundary::SCHEDULING_KEY]
  scope&.active? ? scope.mode : @callback_scheduling
end

#get_prompt(name, arguments = {}) ⇒ Hash

Get a prompt by name (for backward compatibility)

Parameters:

  • name (String) —

    Prompt name

  • arguments (Hash) (defaults to: {}) —

    Arguments to fill in the prompt template

Returns:

  • (Hash) —

    Prompt with filled-in arguments



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 261

def get_prompt(name, arguments = {})
  prompt = @prompts.find { |p| p.name == name }
  raise "Prompt '#{name}' not found" unless prompt

  # Hop off the Fiber scheduler before invoking user code — same reason
  # as `call_tool` above.
  result = FiberBoundary.invoke(scheduling: effective_callback_scheduling) { prompt.generator.call(arguments) }

  # Ensure result has the expected format (symbol or string keys)
  messages = result.is_a?(Hash) ? ClaudeAgentSDK.flexible_fetch(result, "messages", "messages") : nil
  raise "Prompt '#{name}' must return a hash with :messages key" if messages.nil?

  result
end

#handle_json(json_string) ⇒ String

Handle a JSON-RPC request

Parameters:

  • json_string (String) —

    JSON-RPC request

Returns:

  • (String) —

    JSON-RPC response



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 138

def handle_json(json_string)
  @mcp_server.handle_json(json_string)
end

#handle_message(message) ⇒ Hash

Route one JSON-RPC request hash (symbol keys, as produced by the transport) through the official MCP::Server. Two sanitations, both empirically required:

  1. The gem's JsonRpcHandler rejects string ids not matching /\A[a-zA-Z0-9_-]+\z/ with nil, error: -32600 (Python echoes any id verbatim) — swap in a safe id and re-stamp the original on the response (error envelopes too).
  2. The gem rejects messages lacking jsonrpc: '2.0' with -32600; Python never inspects this field and the CLI's embedded mcp_message shape is not guaranteed — force it. NOTE on concurrency: Query runs each control_request in its own async task, so two tools/call can interleave inside the gem's Server#handle. Responses are built from per-call locals (safe), but the gem's instrumentation_callback attribution (@instrumentation_data ivar) can cross-contaminate under concurrency — harmless with the default no-op.

Parameters:

  • message (Hash) —

    JSON-RPC request hash

Returns:

  • (Hash) —

    JSON-RPC response hash



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 159

def handle_message(message)
  original_id = message[:id]
  response = @mcp_server.handle(message.merge(jsonrpc: '2.0', id: 0))
  response[:id] = original_id if response.is_a?(Hash) && response.key?(:id)
  normalize_tools_call_errors(message, response)
end

#list_prompts ⇒ Array<Hash>

List all available prompts (for backward compatibility)

Returns:

  • (Array<Hash>) —

    Array of prompt definitions



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 247

def list_prompts
  @prompts.map do |prompt|
    {
      name: prompt.name,
      description: prompt.description,
      arguments: prompt.arguments
    }.compact
  end
end

#list_resources ⇒ Array<Hash>

List all available resources (for backward compatibility)

Returns:

  • (Array<Hash>) —

    Array of resource definitions



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 214

def list_resources
  @resources.map do |resource|
    {
      uri: resource.uri,
      name: resource.name,
      description: resource.description,
      mimeType: resource.mime_type
    }.compact
  end
end

#list_tools ⇒ Array<Hash>

List all available tools (for backward compatibility)

Returns:

  • (Array<Hash>) —

    Array of tool definitions



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 168

def list_tools
  @tools.map do |tool|
    entry = {
      name: tool.name,
      description: tool.description,
      inputSchema: convert_input_schema(tool.input_schema)
    }
    entry[:annotations] = tool.annotations if tool.annotations
    entry[:_meta] = tool.meta if tool.meta
    entry
  end
end

#read_resource(uri) ⇒ Hash

Read a resource by URI (for backward compatibility)

Parameters:

  • uri (String) —

    Resource URI

Returns:

  • (Hash) —

    Resource content



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# File 'lib/claude_agent_sdk/sdk_mcp_server.rb', line 228

def read_resource(uri)
  resource = @resources.find { |r| r.uri == uri }
  raise "Resource '#{uri}' not found" unless resource

  # Hop off the Fiber scheduler before invoking user code — same reason
  # as `call_tool` above: reader blocks may touch Thread.current-keyed
  # libraries (ActiveRecord, pg, ...) and must run on a plain thread.
  content = FiberBoundary.invoke(scheduling: effective_callback_scheduling) { resource.reader.call }

  # Ensure content has the expected format (symbol or string keys; guard
  # before flexible_fetch — it raises on non-Hash inputs)
  contents = content.is_a?(Hash) ? ClaudeAgentSDK.flexible_fetch(content, "contents", "contents") : nil
  raise "Resource '#{uri}' must return a hash with :contents key" if contents.nil?

  content
end