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new file mode 100644
index 000000000000..2043902c77cd
--- /dev/null
+++ b/awscli/lazy_emitter.py
@@ -0,0 +1,157 @@
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"). You
+# may not use this file except in compliance with the License. A copy of
+# the License is located at
+#
+# http://aws.amazon.com/apache2.0/
+#
+# or in the "license" file accompanying this file. This file is
+# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
+# ANY KIND, either express or implied. See the License for the specific
+# language governing permissions and limitations under the License.
+"""Lazy-initializing event emitter for the AWS CLI plugin system.
+
+LazyInitEmitter wraps a HierarchicalEmitter and uses the plugin registry
+to initialize plugins on demand. Before emitting event X, it finds all
+initializer entries whose event patterns match X (using the same
+prefix/wildcard semantics as HierarchicalEmitter), calls each initializer
+at most once, then delegates to the underlying emitter for normal dispatch.
+"""
+
+import copy
+import importlib
+import logging
+
+from botocore.hooks import HierarchicalEmitter, PrefixTrie
+
+from awscli.handlers_registry import (
+ PLUGIN_REGISTRY,
+ CommandTableOp,
+)
+from awscli.lazy import LazyCommand
+
+logger = logging.getLogger(__name__)
+
+
+class LazyInitEmitter(HierarchicalEmitter):
+ """HierarchicalEmitter that lazily initializes plugins from a registry.
+
+ The registry maps event patterns to lists of (module, fn_name) tuples.
+ Before emitting any event, this emitter checks whether there are
+ uninitialised plugins whose event patterns match the event being emitted.
+ If so, it imports and calls them, then proceeds with normal dispatch.
+ """
+
+ def __init__(self, plugin_registry=None, main_command_table_ops=None):
+ super().__init__()
+ self._init_trie = PrefixTrie()
+ # set of (module, fn_name)
+ self._initialized = set()
+ # number of entries not yet initialized
+ self._pending_count = 0
+ # event_name -> list of entries from init trie
+ self._init_cache: dict[str, list] = {}
+ self._main_ops = main_command_table_ops
+ self._main_ops_applied = False
+ if plugin_registry:
+ self.load_registry(plugin_registry)
+
+ def load_registry(self, registry):
+ unique = set()
+ for event_pattern, entries in registry.items():
+ for entry in entries:
+ self._init_trie.append_item(event_pattern, entry)
+ if entry not in unique:
+ unique.add(entry)
+ self._pending_count += 1
+ self._init_cache = {}
+
+ @property
+ def initialized_count(self):
+ return len(self._initialized)
+
+ def _apply_main_command_table_ops(self, kwargs):
+ """Apply pre-computed renames and LazyCommand additions.
+
+ This replaces the normal lazy-init path for
+ building-command-table.main entries, avoiding the import of
+ heavy plugin modules until the command is actually invoked.
+ """
+ command_table = kwargs.get('command_table')
+ session = kwargs.get('session')
+ if command_table is None or session is None:
+ return
+
+ for op in self._main_ops:
+ if op[0] == CommandTableOp.RENAME:
+ _, old_name, new_name = op
+ if old_name in command_table:
+ current = command_table[old_name]
+ command_table[new_name] = current
+ current.name = new_name
+ del command_table[old_name]
+ elif op[0] == CommandTableOp.ADD:
+ _, cmd_name, cmd_module, cmd_class = op
+ command_table[cmd_name] = LazyCommand(
+ cmd_name,
+ session,
+ cmd_module,
+ cmd_class,
+ )
+ else:
+ raise RuntimeError(f'Unknown command table ops entry: {op}')
+
+ # Mark all building-command-table.main entries as initialized so
+ # _ensure_initialized never imports them. The ops list fully
+ # accounts for all plugins registered against this event.
+ for entry in PLUGIN_REGISTRY.get('building-command-table.main', []):
+ entry = tuple(entry)
+ if entry not in self._initialized:
+ self._initialized.add(entry)
+ self._pending_count -= 1
+
+ def _ensure_initialized(self, event_name):
+ """Initialize any plugins whose event patterns match event_name."""
+ if self._pending_count == 0:
+ return
+ candidates = self._init_cache.get(event_name)
+ if candidates is None:
+ candidates = self._init_trie.prefix_search(event_name)
+ self._init_cache[event_name] = candidates
+ for entry in candidates:
+ if entry not in self._initialized:
+ self._initialized.add(entry)
+ self._pending_count -= 1
+ module_path, fn_name = entry
+ logger.debug(
+ 'Lazy-initializing plugin %s.%s for event %s',
+ module_path,
+ fn_name,
+ event_name,
+ )
+ mod = importlib.import_module(module_path)
+ fn = getattr(mod, fn_name)
+ fn(self)
+
+ def _emit(self, event_name, kwargs, stop_on_response=False):
+ if (
+ self._main_ops
+ and not self._main_ops_applied
+ and event_name == 'building-command-table.main'
+ ):
+ self._main_ops_applied = True
+ self._apply_main_command_table_ops(kwargs)
+ self._ensure_initialized(event_name)
+ return super()._emit(event_name, kwargs, stop_on_response)
+
+ def __copy__(self):
+ new_instance = self.__class__()
+ new_state = self.__dict__.copy()
+ new_state['_handlers'] = copy.copy(self._handlers)
+ new_state['_unique_id_handlers'] = copy.copy(self._unique_id_handlers)
+ new_state['_init_trie'] = copy.copy(self._init_trie)
+ new_state['_initialized'] = copy.copy(self._initialized)
+ new_state['_main_ops_applied'] = self._main_ops_applied
+ new_instance.__dict__ = new_state
+ return new_instance
diff --git a/tests/unit/test_lazy_emitter.py b/tests/unit/test_lazy_emitter.py
new file mode 100644
index 000000000000..281b6d38a6d7
--- /dev/null
+++ b/tests/unit/test_lazy_emitter.py
@@ -0,0 +1,236 @@
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"). You
+# may not use this file except in compliance with the License. A copy of
+# the License is located at
+#
+# http://aws.amazon.com/apache2.0/
+#
+# or in the "license" file accompanying this file. This file is
+# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
+# ANY KIND, either express or implied. See the License for the specific
+# language governing permissions and limitations under the License.
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from awscli.handlers_registry import CommandTableOp
+from awscli.lazy import LazyCommand
+from awscli.lazy_emitter import LazyInitEmitter
+
+
+@pytest.fixture
+def mock_module():
+ """Create a mock module with a callable init function."""
+ module = MagicMock()
+ module.my_init = MagicMock()
+ return module
+
+
+class TestLazyInitEmitterPrefixMatching:
+ def test_bare_prefix_entry_initialized_on_dotted_emit(self, mock_module):
+ registry = {
+ 'building-command-table': [
+ ('test.module', 'my_init'),
+ ],
+ }
+ emitter = LazyInitEmitter()
+ emitter.load_registry(registry)
+
+ with patch('importlib.import_module', return_value=mock_module):
+ emitter.emit('building-command-table.main', command_table={})
+
+ assert emitter.initialized_count == 1
+ mock_module.my_init.assert_called_once()
+
+ def test_exact_match_entry_initialized(self, mock_module):
+ registry = {
+ 'building-command-table.main': [
+ ('test.module', 'my_init'),
+ ],
+ }
+ emitter = LazyInitEmitter()
+ emitter.load_registry(registry)
+
+ with patch('importlib.import_module', return_value=mock_module):
+ emitter.emit('building-command-table.main', command_table={})
+
+ assert emitter.initialized_count == 1
+ mock_module.my_init.assert_called_once()
+
+ def test_unrelated_entry_not_initialized(self, mock_module):
+ registry = {
+ 'building-command-table.ecs': [
+ ('test.module', 'my_init'),
+ ],
+ }
+ emitter = LazyInitEmitter()
+ emitter.load_registry(registry)
+
+ with patch('importlib.import_module', return_value=mock_module):
+ emitter.emit('building-command-table.main', command_table={})
+
+ assert emitter.initialized_count == 0
+ mock_module.my_init.assert_not_called()
+
+ def test_multiple_prefix_levels_all_initialized(self, mock_module):
+ mock_module.other_init = MagicMock()
+ registry = {
+ 'building-command-table': [
+ ('test.module', 'my_init'),
+ ],
+ 'building-command-table.main': [
+ ('test.module', 'other_init'),
+ ],
+ }
+ emitter = LazyInitEmitter()
+ emitter.load_registry(registry)
+
+ with patch('importlib.import_module', return_value=mock_module):
+ emitter.emit('building-command-table.main', command_table={})
+
+ assert emitter.initialized_count == 2
+ mock_module.my_init.assert_called_once()
+ mock_module.other_init.assert_called_once()
+
+ def test_entry_initialized_only_once(self, mock_module):
+ registry = {
+ 'building-command-table': [
+ ('test.module', 'my_init'),
+ ],
+ }
+ emitter = LazyInitEmitter()
+ emitter.load_registry(registry)
+
+ with patch('importlib.import_module', return_value=mock_module):
+ emitter.emit('building-command-table.main', command_table={})
+ emitter.emit('building-command-table.ecs', command_table={})
+
+ assert emitter.initialized_count == 1
+ mock_module.my_init.assert_called_once()
+
+
+class TestMainCommandTableOps:
+ def test_covered_plugins_not_imported(self, mock_module):
+ registry = {
+ 'building-command-table.main': [
+ ('heavy.module', 'register_add_cmd'),
+ ],
+ }
+ main_ops = [
+ (CommandTableOp.ADD, 'my-cmd', 'heavy.module', 'MyCommand'),
+ ]
+ emitter = LazyInitEmitter(main_command_table_ops=main_ops)
+ emitter.load_registry(registry)
+
+ command_table = {'existing': MagicMock(name='existing')}
+ session = MagicMock()
+
+ with (
+ patch('awscli.lazy_emitter.PLUGIN_REGISTRY', registry),
+ patch('importlib.import_module', return_value=mock_module) as imp,
+ ):
+ emitter.emit(
+ 'building-command-table.main',
+ command_table=command_table,
+ session=session,
+ )
+
+ imp.assert_not_called()
+ assert emitter.initialized_count == 1
+
+ def test_rename_op_applied_to_command_table(self):
+ registry = {
+ 'building-command-table.main': [
+ ('rename.module', 'register_rename'),
+ ],
+ }
+ main_ops = [
+ (CommandTableOp.RENAME, 'old-name', 'new-name'),
+ ]
+ emitter = LazyInitEmitter(main_command_table_ops=main_ops)
+ emitter.load_registry(registry)
+
+ cmd = MagicMock()
+ cmd.name = 'old-name'
+ command_table = {'old-name': cmd}
+ session = MagicMock()
+
+ with patch('awscli.lazy_emitter.PLUGIN_REGISTRY', registry):
+ emitter.emit(
+ 'building-command-table.main',
+ command_table=command_table,
+ session=session,
+ )
+
+ assert 'old-name' not in command_table
+ assert 'new-name' in command_table
+ assert command_table['new-name'] is cmd
+ assert cmd.name == 'new-name'
+
+ def test_add_op_creates_lazy_command(self):
+ registry = {
+ 'building-command-table.main': [
+ ('add.module', 'register_add'),
+ ],
+ }
+ main_ops = [
+ (CommandTableOp.ADD, 'my-cmd', 'add.module.impl', 'MyCommand'),
+ ]
+ emitter = LazyInitEmitter(main_command_table_ops=main_ops)
+ emitter.load_registry(registry)
+
+ command_table = {}
+ session = MagicMock()
+
+ with patch('awscli.lazy_emitter.PLUGIN_REGISTRY', registry):
+ emitter.emit(
+ 'building-command-table.main',
+ command_table=command_table,
+ session=session,
+ )
+
+ assert 'my-cmd' in command_table
+ assert isinstance(command_table['my-cmd'], LazyCommand)
+ assert command_table['my-cmd'].name == 'my-cmd'
+
+ def test_main_ops_skips_covered_but_initializes_bare_prefix(
+ self, mock_module
+ ):
+ registry = {
+ 'building-command-table': [
+ ('global.module', 'register_global'),
+ ],
+ 'building-command-table.main': [
+ ('heavy.module', 'register_add_cmd'),
+ ],
+ }
+ main_ops = [
+ (CommandTableOp.ADD, 'my-cmd', 'heavy.module', 'MyCommand'),
+ ]
+ emitter = LazyInitEmitter(main_command_table_ops=main_ops)
+ emitter.load_registry(registry)
+
+ command_table = {}
+ session = MagicMock()
+
+ mock_global = MagicMock()
+ mock_global.register_global = MagicMock()
+
+ def import_side_effect(mod_path):
+ if mod_path == 'global.module':
+ return mock_global
+ raise AssertionError(f'Unexpected import of {mod_path!r}')
+
+ with (
+ patch('awscli.lazy_emitter.PLUGIN_REGISTRY', registry),
+ patch('importlib.import_module', side_effect=import_side_effect),
+ ):
+ emitter.emit(
+ 'building-command-table.main',
+ command_table=command_table,
+ session=session,
+ )
+
+ mock_global.register_global.assert_called_once()
+ assert emitter.initialized_count == 2
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