Class: Prescient::MCP::Rack

Inherits:
Object
  • Object
show all
Defined in:
lib/prescient/mcp/rack.rb

Overview

Optional Rack-compatible MCP HTTP handler with explicit authentication. rubocop:disable Metrics/ClassLength

Constant Summary collapse

PROTOCOL_VERSION =

MCP protocol version supported by the HTTP transport.

Returns:

  • (String) —

    Protocol version identifier

"2025-06-18"
SESSION_HEADER =

Rack environment key containing the MCP session identifier.

Returns:

  • (String) —

    Rack header key

"HTTP_MCP_SESSION_ID"
PROTOCOL_HEADER =

Rack environment key containing the MCP protocol version.

Returns:

  • (String) —

    Rack header key

"HTTP_MCP_PROTOCOL_VERSION"
ALLOWED_ORIGINS_DEFAULT =

Default policy allowing requests without an Origin header restriction.

Returns:

  • (Array<String>) —

    Empty Origin allowlist

[].freeze

Instance Method Summary collapse

Constructor Details

#initialize(authentication:, server: Server.new, request_context: nil, max_body_bytes: Configuration::DEFAULT_MAX_INPUT_BYTES, allowed_origins: ALLOWED_ORIGINS_DEFAULT, session_ttl: 3600) ⇒ Rack

Returns a new instance of Rack.



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# File 'lib/prescient/mcp/rack.rb', line 26

def initialize(authentication:, server: Server.new, request_context: nil,
               max_body_bytes: Configuration::DEFAULT_MAX_INPUT_BYTES,
               allowed_origins: ALLOWED_ORIGINS_DEFAULT, session_ttl: 3600)
  @server = server
  @authentication = authentication
  @request_context = request_context
  @max_body_bytes = validate_limit(max_body_bytes)
  @allowed_origins = Array(allowed_origins).map(&:to_s).freeze
  @session_ttl = validate_session_ttl(session_ttl)
  @sessions = {}
  @sessions_lock = Monitor.new
end

Instance Method Details

#call(env) ⇒ Array

Handle one MCP Streamable HTTP request.

Parameters:

  • env (Hash) —

    Rack environment

Returns:

  • (Array) —

    Rack response



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# File 'lib/prescient/mcp/rack.rb', line 42

def call(env)
  method = env.fetch("REQUEST_METHOD", "GET").upcase
  unless %w[POST GET DELETE].include?(method)
    return response(
      405, { error: "method_not_allowed" }, { "allow" => "POST, GET, DELETE" }
    )
  end
  return response(403, { error: "origin_not_allowed" }) unless origin_allowed?(env)

  authentication = authenticate(env)
  unless authentication
    return response(401, { error: "authentication_required" }, { "www-authenticate" => "Bearer" })
  end

  return post(env, authentication) if method == "POST"
  return get(env, authentication) if method == "GET"

  delete(env, authentication)
rescue JSON::ParserError
  response(400, { error: "invalid_json" })
rescue SessionNotFoundError
  response(404, { error: "session_not_found" })
rescue AuthenticationError
  response(401, { error: "authentication_failed" })
rescue ArgumentError
  response(400, { error: "invalid_request" })
rescue StandardError
  response(500, { error: "internal_error" })
end