Files
shopdb-flask/shopdb/plugins/loader.py
cproudlock 5b19f3b554 ADR-013 Phase 2: enforcement + signed shelf + adopt
Completes the marketplace security model. Verification stops being advisory:
a plugin only loads or migrates when its tree matches a trusted signature, and
plugins are pulled from a signed shelf with anti-rollback and revocation.

Enforcement (default OFF - existing deploys unchanged):
- verification.py PluginVerifier, shared by the loader (verify-at-load, before
  plugin.py is imported) and the migration manager (verify-at-migrate, before
  any DDL). Fail-closed: an unsigned/tampered/wrong-key plugin does not run.
- Gated by PLUGIN_REQUIRE_SIGNED. PLUGIN_DEV_TRUST_DIRS exempts named dirs but
  only under DEBUG/TESTING; production ignores it.
- flask plugin stamp-bundled writes provenance into in-tree plugins so
  verify-at-load applies to bundled plugins too (image build step).
- tier:core manifest guard: uninstall/disable refuse a core-tier plugin.

Shelf (shelf.py):
- Signed shelf-index.json (+ .sig): monotonic serial (a site refuses an older
  index - anti-rollback), revoked list carried across builds, per-entry
  version/tier/core_version for browse. Index is a browse layer only; adopt
  reads security-bearing fields from the verified artifact.
- flask plugin shelf-build / shelf-list / adopt / audit. adopt verifies index +
  artifact (signature + every file hash), unpacks to staging, re-verifies, then
  atomically moves into place and installs+enables the closure. Refuses a
  downgrade without --force-downgrade. Anti-rollback serial stored in
  instance/shelf-state.json.
- config PLUGIN_SHELF_DIR; the app only reads the folder, never speaks a
  network. .env.example + docs/PLUGIN-SIGNING.md document the flow.

22 tests: verifier policy (off / no-keys / signed / tampered / wrong-key /
dev-exempt), verify-at-load + verify-at-migrate integration, tier guard, index
sign/verify + tamper/wrong-key, serial state, revocation, version resolution,
verified atomic unpack + tamper refusal. Live-smoked keygen->pack->shelf-build
->list->adopt->audit + serial guard. 1050 pass, naming green.
2026-07-18 20:44:54 -04:00

301 lines
11 KiB
Python

"""Plugin discovery and loading.
The loader reads each plugin's manifest.json before instantiating the
plugin class. Dependency sorting and contract-version compatibility
checks operate on manifests, not plugin instances. The plugin class is
imported and instantiated only after the manifest passes validation.
Failure policy (per the enforcing-plugin-contract skill):
- In dev/test (app.config.DEBUG or TESTING true): re-raise the original
exception so failures are loud.
- In production: log the failure with full context and exclude the
plugin from registration. The framework keeps booting.
"""
import importlib
import importlib.util
import json
import logging
from pathlib import Path
from typing import Dict, List, Type, Optional
from flask import Flask
from packaging.specifiers import SpecifierSet, InvalidSpecifier
from packaging.version import Version, InvalidVersion
from .base import BasePlugin
from .registry import PluginRegistry
from ..exceptions import (
PluginError,
PluginNotFoundError,
PluginContractError,
PluginVersionError,
PluginDependencyError,
)
logger = logging.getLogger(__name__)
class PluginLoader:
"""Discovers and loads plugins from the plugins directory."""
def __init__(self, plugins_dir: Path, registry: PluginRegistry):
self.plugins_dir = plugins_dir
self.registry = registry
self._loaded_plugins: Dict[str, BasePlugin] = {}
self._plugin_classes: Dict[str, Type[BasePlugin]] = {}
self._manifests: Dict[str, dict] = {}
# Set by PluginManager.init_app; a PluginVerifier or None (no policy).
self.verifier = None
def _is_strict_mode(self, app: Optional[Flask]) -> bool:
"""Return True if loader should re-raise instead of isolating failures."""
if app is None:
return True
return bool(app.config.get('DEBUG') or app.config.get('TESTING'))
def _handle_failure(self, app: Optional[Flask], exc: Exception, name: str) -> None:
"""In strict mode re-raise; in production log with context and continue."""
if self._is_strict_mode(app):
raise exc
logger.exception(f'Plugin {name} failed to load: {exc}')
def discover_plugins(self) -> List[str]:
"""Discover available plugins in plugins directory."""
available = []
if not self.plugins_dir.exists():
return available
for item in self.plugins_dir.iterdir():
if not item.is_dir():
continue
if (item / 'plugin.py').exists():
available.append(item.name)
return available
def load_manifest(self, name: str) -> dict:
"""Load the plugin's manifest.json.
Raises PluginNotFoundError if the manifest does not exist or is
unparseable. The result is cached.
"""
if name in self._manifests:
return self._manifests[name]
manifest_path = self.plugins_dir / name / 'manifest.json'
if not manifest_path.exists():
raise PluginNotFoundError(
f'Plugin {name} has no manifest.json at {manifest_path}',
plugin_name=name,
)
try:
with open(manifest_path) as f:
manifest = json.load(f)
except json.JSONDecodeError as e:
raise PluginContractError(
f'Plugin {name} has invalid manifest.json: {e}',
plugin_name=name,
) from e
for required in ('name', 'version', 'description'):
if not manifest.get(required):
raise PluginContractError(
f'Plugin {name} manifest.json missing required field "{required}"',
plugin_name=name,
)
if manifest['name'] != name:
raise PluginContractError(
f'Plugin directory "{name}" does not match manifest name "{manifest["name"]}"',
plugin_name=name,
)
self._manifests[name] = manifest
return manifest
def check_contract_version(self, name: str, contract_version: str) -> None:
"""Verify the plugin's core_version range includes contract_version.
Raises PluginVersionError on mismatch.
"""
manifest = self.load_manifest(name)
core_version_spec = manifest.get('core_version', '')
if not core_version_spec:
return
try:
specifier = SpecifierSet(core_version_spec)
framework_version = Version(contract_version)
except (InvalidSpecifier, InvalidVersion) as e:
raise PluginContractError(
f'Plugin {name} has invalid version specifier "{core_version_spec}": {e}',
plugin_name=name,
) from e
if framework_version not in specifier:
raise PluginVersionError(
f'Plugin {name} requires core_version {core_version_spec} '
f'but framework is at {contract_version}',
plugin_name=name,
)
def load_plugin_class(self, name: str) -> Type[BasePlugin]:
"""Import the plugin's plugin.py and return the BasePlugin subclass.
Raises PluginNotFoundError if plugin.py is missing.
Raises PluginContractError if the module has no BasePlugin subclass
or import fails.
"""
if name in self._plugin_classes:
return self._plugin_classes[name]
plugin_module_path = self.plugins_dir / name / 'plugin.py'
if not plugin_module_path.exists():
raise PluginNotFoundError(
f'Plugin {name} plugin.py not found at {plugin_module_path}',
plugin_name=name,
)
try:
spec = importlib.util.spec_from_file_location(
f'plugins.{name}.plugin', plugin_module_path,
)
module = importlib.util.module_from_spec(spec)
spec.loader.exec_module(module)
except Exception as e:
raise PluginContractError(
f'Plugin {name} import failed: {e}',
plugin_name=name,
) from e
for attr_name in dir(module):
attr = getattr(module, attr_name)
if (isinstance(attr, type)
and issubclass(attr, BasePlugin)
and attr is not BasePlugin):
self._plugin_classes[name] = attr
return attr
raise PluginContractError(
f'Plugin {name} module has no BasePlugin subclass',
plugin_name=name,
)
def load_plugin(self, name: str, app: Flask, db) -> Optional[BasePlugin]:
"""Load and instantiate a plugin.
Returns the plugin instance on success. In strict mode (dev/test),
any failure raises. In production, returns None and logs the
failure with full context.
"""
if name in self._loaded_plugins:
return self._loaded_plugins[name]
try:
from shopdb import __contract_version__
manifest = self.load_manifest(name)
self.check_contract_version(name, __contract_version__)
# verify-at-load: refuse to import plugin.py unless the tree matches
# a trusted signature (when the site enforces it). Runs BEFORE any
# plugin code is imported, so a tampered/unsigned plugin never runs.
if self.verifier is not None:
ok, reason = self.verifier.check(name)
if not ok:
raise PluginError(
f'Plugin {name} failed signature verification: {reason}',
plugin_name=name,
)
for dep in manifest.get('dependencies', []):
if not self.registry.is_enabled(dep):
raise PluginDependencyError(
f'Plugin {name} requires {dep} which is not enabled',
plugin_name=name,
)
plugin_class = self.load_plugin_class(name)
plugin = plugin_class()
plugin.init_app(app, db)
self._loaded_plugins[name] = plugin
return plugin
except PluginError as e:
self._handle_failure(app, e, name)
return None
except Exception as e:
wrapped = PluginError(
f'Unexpected failure loading plugin {name}: {e}',
plugin_name=name,
)
self._handle_failure(app, wrapped, name)
return None
def load_enabled_plugins(self, app: Flask, db) -> Dict[str, BasePlugin]:
"""Load all enabled plugins in dependency order."""
loaded = {}
enabled = self.registry.get_enabled_plugins()
sorted_plugins = self._sort_by_dependencies(enabled)
for name in sorted_plugins:
plugin = self.load_plugin(name, app, db)
if plugin:
loaded[name] = plugin
logger.info(f'Loaded plugin: {name} v{plugin.meta.version}')
return loaded
def _sort_by_dependencies(self, plugin_names: List[str]) -> List[str]:
"""Sort plugins so dependencies come first.
Reads dependencies from manifest.json directly; does not
instantiate plugin classes during sort. Detects a dependency cycle
(a back edge in the DFS) and raises PluginDependencyError rather than
looping or silently dropping a plugin.
"""
sorted_list = []
visited = set() # fully processed (post-order emitted)
visiting = set() # on the current DFS stack; a revisit here is a cycle
def visit(name):
if name in visited:
return
if name in visiting:
raise PluginDependencyError(
f'Circular plugin dependency involving "{name}"',
plugin_name=name,
)
visiting.add(name)
# Only the manifest read is tolerant; a cycle raised by a nested
# visit must propagate, so the dep recursion sits outside the guard
# (PluginDependencyError is itself a PluginError).
try:
deps = self.load_manifest(name).get('dependencies', [])
except PluginError:
deps = []
for dep in deps:
if dep in plugin_names:
visit(dep)
visiting.discard(name)
visited.add(name)
sorted_list.append(name)
for name in plugin_names:
visit(name)
return sorted_list
def get_loaded_plugin(self, name: str) -> Optional[BasePlugin]:
"""Get an already loaded plugin."""
return self._loaded_plugins.get(name)
def get_all_loaded(self) -> Dict[str, BasePlugin]:
"""Get all loaded plugins."""
return self._loaded_plugins.copy()