Fix connection leaks in broker and transport access

[ShubhAtWork]

Summary

Several places call capp.connection() without using a context manager, creating AMQP/Redis connections that are never closed. Each leaked connection holds open a socket and file descriptor. Under sustained use (e.g. the Broker view refreshing, or /api/queues/length being polled by monitoring), this causes gradual file descriptor exhaustion, eventually leading to Too many open files errors that crash the process.

Leaks fixed

Location	Problem	Fix
Flower.transport property	Called on every request that checks broker type. Opens connection, reads driver type, discards without closing.	Cache the result (transport type never changes at runtime) + context manager for initial lookup
print_banner()	app.connection().as_uri() opens a connection to format the broker URL for the startup log. Never closed.	Context manager
BrokerView.get()	Two separate capp.connection() calls — one for Broker creation, one for display URL. Neither closed.	Single context-managed connection for both
GetQueueLengths.get()	capp.connection().as_uri() opens a connection to get broker URI. Never closed.	Context manager
WorkersView.get()	capp.connection().as_uri() opens a connection on every non-JSON page render. Never closed.	Context manager

Test plan

• Verify existing tests pass — no behavioral change, only resource management
• In long-running deployment, confirm no file descriptor growth over time (lsof -p <pid> | wc -l)

🤖 Generated with Claude Code

[mher]

I suggest doing something like this instead

  from functools import cached_property

  class Flower(tornado.web.Application):
      @cached_property
      def broker_uri(self):
          with self.capp.connection() as conn:
              return conn.as_uri()

      @cached_property
      def broker_uri_with_password(self):
          with self.capp.connection() as conn:
              return conn.as_uri(include_password=True)

      @cached_property
      def transport(self):
          with self.capp.connection() as conn:
              return getattr(conn.transport, "driver_type", None)