chore: Extract shared sans-I/O cores and add config read-protocols

CONTRIBUTING.md

@@ -78,6 +78,10 @@ A special case is the module `ldclient.impl`, and any modules within it. Everyth
 
 So, if there is a class whose existence is entirely an implementation detail, it should be in `impl`. Similarly, classes that are _not_ in `impl` must not expose any public members (i.e. symbols that do not have an underscore prefix) that are not meant to be part of the supported public API. This is important because of our guarantee of backward compatibility for all public APIs within a major version: we want to be able to change our implementation details to suit the needs of the code, without worrying about breaking a customer's code. Due to how the language works, we can't actually prevent an application developer from referencing those classes in their code, but this convention makes it clear that such use is discouraged and unsupported.
 
+### Sync/async parity
+
+The SDK maintains parallel sync (`foo.py`) and async (`async_foo.py`) implementations by hand. When you change a method in a sync module, make the matching change in its `async_` sibling (and vice versa), and justify any difference beyond `async`/`await` keywords. Shared I/O-free ("sans-I/O") logic lives in modules with a `_common` suffix that are imported by both siblings: `impl/client_common.py`, `impl/datasystem/fdv2_common.py`, and `impl/events/event_processor_common.py`. Per-side logic that genuinely differs (more than `async`/`await`) lives directly in each sibling, not in a separate `_common` module — for example `impl/evaluator.py`/`impl/async_evaluator.py` and the in-memory feature stores `feature_store.py`/`async_feature_store.py`. Both the sync and async contract test suites must pass.
+
 ### Type hints
 
 Python does not require the use of type hints, but they can be extremely helpful for spotting mistakes and for improving the IDE experience, so we should always use them in the SDK. Every method in the public API is expected to have type hints for all non-`self` parameters, and for its return value if any.

ldclient/client.py

@@ -2,8 +2,6 @@
 This submodule contains the client class that provides most of the SDK functionality.
 """
 
-import hashlib
-import hmac
 import threading
 import traceback
 from typing import Any, Callable, Dict, List, Mapping, Optional, Tuple
@@ -19,6 +17,11 @@
     _EvaluationWithHookResult
 )
 from ldclient.impl.big_segments import BigSegmentStoreManager
+from ldclient.impl.client_common import (
+    get_environment_metadata,
+    get_plugin_hooks
+)
+from ldclient.impl.client_common import secure_mode_hash as _secure_mode_hash
 from ldclient.impl.datasource.feature_requester import FeatureRequesterImpl
 from ldclient.impl.datasource.polling import PollingUpdateProcessor
 from ldclient.impl.datasource.status import (
@@ -57,12 +60,7 @@
     ReadOnlyStore
 )
 from ldclient.migrations import OpTracker, Stage
-from ldclient.plugin import (
-    ApplicationMetadata,
-    EnvironmentMetadata,
-    SdkMetadata
-)
-from ldclient.version import VERSION
+from ldclient.plugin import EnvironmentMetadata
 from ldclient.versioned_data_kind import FEATURES, SEGMENTS, VersionedDataKind
 
 from .impl import AnyNum
@@ -239,8 +237,8 @@ def postfork(self, start_wait: float = 5):
         self.__start_up(start_wait)
 
     def __start_up(self, start_wait: float):
-        environment_metadata = self.__get_environment_metadata()
-        plugin_hooks = self.__get_plugin_hooks(environment_metadata)
+        environment_metadata = get_environment_metadata(self._config, "python-server-sdk")
+        plugin_hooks = get_plugin_hooks(self._config, environment_metadata)
 
         self.__hooks_lock = ReadWriteLock()
         self.__hooks = self._config.hooks + plugin_hooks  # type: List[Hook]
@@ -305,36 +303,6 @@ def __start_up(self, start_wait: float):
         else:
             log.warning("Initialization timeout exceeded for LaunchDarkly Client or an error occurred. " "Feature Flags may not yet be available.")
 
-    def __get_environment_metadata(self) -> EnvironmentMetadata:
-        sdk_metadata = SdkMetadata(
-            name="python-server-sdk",
-            version=VERSION,
-            wrapper_name=self._config.wrapper_name,
-            wrapper_version=self._config.wrapper_version
-        )
-
-        application_metadata = None
-        if self._config.application:
-            application_metadata = ApplicationMetadata(
-                id=self._config.application.get('id'),
-                version=self._config.application.get('version'),
-            )
-
-        return EnvironmentMetadata(
-            sdk=sdk_metadata,
-            application=application_metadata,
-            sdk_key=self._config.sdk_key
-        )
-
-    def __get_plugin_hooks(self, environment_metadata: EnvironmentMetadata) -> List[Hook]:
-        hooks = []
-        for plugin in self._config.plugins:
-            try:
-                hooks.extend(plugin.get_hooks(environment_metadata))
-            except Exception as e:
-                log.error("Error getting hooks from plugin %s: %s", plugin.metadata.name, e)
-        return hooks
-
     def __register_plugins(self, environment_metadata: EnvironmentMetadata):
         for plugin in self._config.plugins:
             try:
@@ -693,10 +661,7 @@ def secure_mode_hash(self, context: Context) -> str:
         :param context: the evaluation context
         :return: the hash string
         """
-        if not context.valid:
-            log.warning("Context was invalid for secure_mode_hash (%s); returning empty hash" % context.error)
-            return ""
-        return hmac.new(str(self._config.sdk_key).encode(), context.fully_qualified_key.encode(), hashlib.sha256).hexdigest()
+        return _secure_mode_hash(self._config, context)
 
     def add_hook(self, hook: Hook):
         """

ldclient/config.py

@@ -160,12 +160,87 @@ def disable_ssl_verification(self) -> bool:
 T_co = TypeVar("T_co", covariant=True)
 
 
+class SdkIdentityConfig(Protocol):
+    """
+    The SDK's self-identity fields — read by the shared environment-metadata and
+    secure-mode helpers, and included in request headers.
+    """
+
+    @property
+    def sdk_key(self) -> Optional[str]:
+        """The SDK key used to authenticate requests."""
+
+    @property
+    def application(self) -> dict:
+        """The application metadata included in request headers."""
+
+    @property
+    def wrapper_name(self) -> Optional[str]:
+        """The wrapper name included in request headers."""
+
+    @property
+    def wrapper_version(self) -> Optional[str]:
+        """The wrapper version included in request headers."""
+
+
+class DataSourceBuilderConfig(SdkIdentityConfig, Protocol):
+    """
+    The subset of configuration that data source builders and the data sources
+    they build read. Extends :class:`SdkIdentityConfig` with the transport and
+    endpoint fields. It is the structural contract a config object must satisfy
+    to be passed to :meth:`DataSourceBuilder.build`.
+    """
+
+    @property
+    def base_uri(self) -> str:
+        """The base URI for polling requests."""
+
+    @property
+    def stream_base_uri(self) -> str:
+        """The base URI for streaming requests."""
+
+    @property
+    def http(self) -> HTTPConfig:
+        """The HTTP configuration used for requests."""
+
+    @property
+    def initial_reconnect_delay(self) -> float:
+        """The initial reconnect delay for the streaming data source."""
+
+    @property
+    def poll_interval(self) -> float:
+        """The interval between polling requests."""
+
+    @property
+    def payload_filter_key(self) -> Optional[str]:
+        """The payload filter key applied as a query parameter."""
+
+    # Set by the client after construction, so it is a read-write attribute
+    # rather than a read-only property.
+    _instance_id: Optional[str]
+
+
+class PrivateAttributesConfig(Protocol):
+    """
+    The private-attribute redaction settings read by the event output formatter
+    when building analytics events.
+    """
+
+    @property
+    def all_attributes_private(self) -> bool:
+        """Whether all context attributes should be treated as private."""
+
+    @property
+    def private_attributes(self) -> List[str]:
+        """The context attribute references to treat as private."""
+
+
 class DataSourceBuilder(Protocol[T_co]):  # pylint: disable=too-few-public-methods
     """
     Protocol for building data sources.
     """
 
-    def build(self, config: 'Config') -> T_co:
+    def build(self, config: DataSourceBuilderConfig) -> T_co:
         """
         Builds the data source.
 
@@ -199,7 +274,7 @@ class DataSystemConfig:
     """An optional fallback synchronizer that will read from FDv1"""
 
 
-class Config:
+class Config(DataSourceBuilderConfig, PrivateAttributesConfig):
     """Advanced configuration options for the SDK client.
 
     To use these options, create an instance of ``Config`` and pass it to either :func:`ldclient.set_config()`

ldclient/impl/client_common.py

@@ -0,0 +1,66 @@
+"""
+Genuinely I/O-free, await-free helpers shared by the sync :class:`ldclient.client.LDClient`
+and async :class:`ldclient.async_client.AsyncLDClient`.
+
+These functions contain no awaits and touch no store/network/event I/O, so they
+can live in a single module imported by both clients. Anything that reads the
+store, sends events, or runs hook stages is I/O-adjacent and is hand-duplicated
+across the two client classes instead (differing only in ``async``/``await``).
+"""
+
+import hashlib
+import hmac
+from typing import List
+
+from ldclient.config import Config, SdkIdentityConfig
+from ldclient.context import Context
+from ldclient.hook import Hook
+from ldclient.impl.util import log
+from ldclient.plugin import (
+    ApplicationMetadata,
+    EnvironmentMetadata,
+    SdkMetadata
+)
+from ldclient.version import VERSION
+
+
+def get_environment_metadata(config: SdkIdentityConfig, sdk_name: str) -> EnvironmentMetadata:
+    sdk_metadata = SdkMetadata(
+        name=sdk_name,
+        version=VERSION,
+        wrapper_name=config.wrapper_name,
+        wrapper_version=config.wrapper_version
+    )
+
+    application_metadata = None
+    if config.application:
+        application_metadata = ApplicationMetadata(
+            id=config.application.get('id'),
+            version=config.application.get('version'),
+        )
+
+    return EnvironmentMetadata(
+        sdk=sdk_metadata,
+        application=application_metadata,
+        sdk_key=config.sdk_key
+    )
+
+
+def get_plugin_hooks(config: Config, environment_metadata: EnvironmentMetadata) -> List[Hook]:
+    hooks = []
+    for plugin in config.plugins:
+        try:
+            hooks.extend(plugin.get_hooks(environment_metadata))
+        except Exception as e:
+            log.error("Error getting hooks from plugin %s: %s", plugin.metadata.name, e)
+    return hooks
+
+
+def secure_mode_hash(config: SdkIdentityConfig, context: Context) -> str:
+    """Computes the secure-mode HMAC for a context, or an empty string for an
+    invalid context. Pure: depends only on the SDK key and the context's
+    fully-qualified key."""
+    if not context.valid:
+        log.warning("Context was invalid for secure_mode_hash (%s); returning empty hash" % context.error)
+        return ""
+    return hmac.new(str(config.sdk_key).encode(), context.fully_qualified_key.encode(), hashlib.sha256).hexdigest()

ldclient/impl/datasourcev2/polling.py

@@ -13,7 +13,11 @@
 
 import urllib3
 
-from ldclient.config import Config, DataSourceBuilder, HTTPConfig
+from ldclient.config import (
+    DataSourceBuilder,
+    DataSourceBuilderConfig,
+    HTTPConfig
+)
 from ldclient.impl.datasource.feature_requester import FDV1_POLLING_ENDPOINT
 from ldclient.impl.datasystem.protocolv2 import (
     DeleteObject,
@@ -257,7 +261,7 @@ class Urllib3PollingRequester(Requester):
     requests.
     """
 
-    def __init__(self, config: Config, base_uri: str, http_options: HTTPConfig):
+    def __init__(self, config: DataSourceBuilderConfig, base_uri: str, http_options: HTTPConfig):
         self._etag = None
         factory = HTTPFactory(_base_headers(config), http_options)
         self._http = factory.create_pool_manager(1, base_uri)
@@ -422,7 +426,7 @@ def requester(self, requester: Requester) -> 'PollingDataSourceBuilder':
         self.__requester = requester
         return self
 
-    def build(self, config: Config) -> PollingDataSource:
+    def build(self, config: DataSourceBuilderConfig) -> PollingDataSource:
         """Builds the PollingDataSource with the configured parameters."""
         requester = (
             self.__requester
@@ -465,7 +469,7 @@ def http_options(self, http_options: HTTPConfig) -> 'FallbackToFDv1PollingDataSo
         self.__http_options = http_options
         return self
 
-    def build(self, config: Config) -> PollingDataSource:
+    def build(self, config: DataSourceBuilderConfig) -> PollingDataSource:
         """Builds the PollingDataSource with the configured parameters."""
         builder = PollingDataSourceBuilder()
         builder.requester(
@@ -487,7 +491,7 @@ class Urllib3FDv1PollingRequester(Requester):
     requests.
     """
 
-    def __init__(self, config: Config, base_uri: str, http_options: HTTPConfig):
+    def __init__(self, config: DataSourceBuilderConfig, base_uri: str, http_options: HTTPConfig):
         self._etag = None
         self._http = HTTPFactory(_base_headers(config), http_options).create_pool_manager(
             1, base_uri

ldclient/impl/datasourcev2/streaming.py

@@ -18,7 +18,11 @@
 )
 from ld_eventsource.errors import HTTPStatusError
 
-from ldclient.config import Config, DataSourceBuilder, HTTPConfig
+from ldclient.config import (
+    DataSourceBuilder,
+    DataSourceBuilderConfig,
+    HTTPConfig
+)
 from ldclient.impl.datasystem import DiagnosticAccumulator, DiagnosticSource
 from ldclient.impl.datasystem.protocolv2 import (
     DeleteObject,
@@ -59,7 +63,7 @@
 STREAMING_ENDPOINT = "/sdk/stream"
 
 SseClientBuilder = Callable[
-    [str, HTTPConfig, float, Config, SelectorStore],
+    [str, HTTPConfig, float, DataSourceBuilderConfig, SelectorStore],
     Tuple[SSEClient, Optional[urllib3.PoolManager]],
 ]
 
@@ -68,7 +72,7 @@ def create_sse_client(
     base_uri: str,
     http_options: HTTPConfig,
     initial_reconnect_delay: float,
-    config: Config,
+    config: DataSourceBuilderConfig,
     ss: SelectorStore
 ) -> Tuple[SSEClient, Optional[urllib3.PoolManager]]:
     """ "
@@ -158,7 +162,7 @@ def __init__(self,
                  uri: str,
                  http_options: HTTPConfig,
                  initial_reconnect_delay: float,
-                 config: Config):
+                 config: DataSourceBuilderConfig):
         self.__uri = uri
         self.__http_options = http_options
         self.__initial_reconnect_delay = initial_reconnect_delay
@@ -519,7 +523,7 @@ def http_options(self, http_options: HTTPConfig) -> 'StreamingDataSourceBuilder'
         self.__http_options = http_options
         return self
 
-    def build(self, config: Config) -> StreamingDataSource:
+    def build(self, config: DataSourceBuilderConfig) -> StreamingDataSource:
         """Builds a StreamingDataSource instance with the configured parameters."""
         return StreamingDataSource(
             self.__base_uri or config.stream_base_uri,