Class: DebugMcp::Tools::RailsRecentEvents

Inherits:
MCP::Tool
  • Object
show all
Defined in:
lib/debug_mcp/tools/rails_recent_events.rb

Overview

Read recent Rails internal events (SQL, render, cache, job enqueue, request lifecycle) from the in-process Notifications buffer, independent of trigger_request.

IMPORTANT semantics, surfaced in every response so the model does not mistake “empty” for “nothing happened”:

  • forward-only: only events fired AFTER the subscriber was installed are visible. The first call installs the subscriber, so it usually returns little or nothing — that is not evidence that no SQL/jobs ran.

  • paused-only: the target must be paused at a debugger prompt (we send commands over the debug socket).

  • NOT read-only: installing the subscriber subscribes to ActiveSupport::Notifications inside the target — an in-process instrumentation side effect (no application data is written).

Constant Summary collapse

DEFAULT_LIMIT = 
50
MAX_LIMIT = 
500
KIND_MATCHERS = 
{
  "sql" => ->(name) { name == "sql.active_record" },
  "render" => ->(name) { name.start_with?("render_") },
  "cache" => ->(name) { name.start_with?("cache_") },
  "job" => ->(name) { name == "enqueue.active_job" },
  "request" => ->(name) { name.end_with?(".action_controller") },
}.freeze

Class Method Summary collapse

Class Method Details

.call(kinds: nil, limit: nil, after_seq: nil, include_debug_eval: false, session_id: nil, server_context:) ⇒ Object 



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# File 'lib/debug_mcp/tools/rails_recent_events.rb', line 82

def call(kinds: nil, limit: nil, after_seq: nil, include_debug_eval: false, session_id: nil,
         server_context:)
  client = server_context[:session_manager].client(session_id)
  client.auto_repause!
  RailsHelper.require_rails!(client)

  # Reads and install both send commands over the debug socket and both
  # take the buffer/Notifications mutex, which fails in trap context.
  if RailsHelper.trap_context?(client)
    return text_response("Rails recent events: unavailable in trap context.\n\n" \
                         "#{RailsHelper::TRAP_CONTEXT_HINT}")
  end

  installed = NotificationsSubscriber.install(client)
  unless installed
    return text_response("Rails recent events: could not install the Notifications subscriber " \
                         "in the target process.\n\n#{RailsHelper::TRAP_CONTEXT_HINT}")
  end

  limit = resolve_limit(limit)
  events = fetch_events(client, after_seq: after_seq, limit: limit)
  events = filter_by_kinds(events, kinds)
  metadata = NotificationsSubscriber.metadata(client)

  # `installed` is the result of the install we just performed — the only
  # trustworthy signal here. metadata[:installed] can be missing if the
  # metadata round-trip itself returned no parseable object.
  text_response(build_output(events, metadata, kinds, include_debug_eval, limit, installed))
rescue DebugMcp::Error => e
  text_response("Error: #{e.message}")
end