feat: Add async FDv1 streaming and data source status tracking

[jsonbailey]

Overview

Adds the async FDv1 streaming data source and its companion async data source status tracking, plus a new shared sans-I/O datasource_common module. This is one slice of the async Python SDK work.

What's included

• Async FDv1 streaming data source (ldclient/impl/datasource/async_streaming.py) — driven by ld_eventsource's AsyncSSEClient and owning its own aiohttp session via make_client_session. It consumes SSE put/patch/delete events and pushes the resulting data into the async data source update sink.

• Async data source status tracking (ldclient/impl/datasource/async_status.py — AsyncDataSourceUpdateSinkImpl and friends). The streaming source pushes data and status transitions into this update sink, so the two are runtime-coupled and land together in this slice.

• New shared sans-I/O datasource_common module (ldclient/impl/datasource/datasource_common.py) — STREAM_ALL_PATH, sink_or_store, and parse_path. Both the sync data sources and the new async streaming source use it.

• Behavior-preserving extraction of the sync data sources. streaming.py and polling.py are routed through datasource_common: the inline _sink_or_store/_parse_path/STREAM_ALL_PATH/ParsedPath definitions are removed in favor of importing the shared helpers, with call sites switched accordingly. No behavior change. The shared module is also needed by the upcoming async polling slice.

• Unified status provider (sync/async). The async status provider was unified with the sync one: the redundant AsyncDataSourceStatusProviderImpl (which had no async-specific behavior — byte-identical to the sync provider apart from its sink type) is removed, and the async data system now reuses the sync DataSourceStatusProviderImpl. To let both sinks satisfy it structurally, the sync provider's update_sink parameter was widened to a small status-only Protocol (_DataSourceStatusSource). This is the same interface-segregation pattern as the PR 1b config read-protocols and mirrors the already-unified big-segment status provider. This adds a small behavior-preserving change to sync status.py.

Notes

• The async public class carries the experimental .. caution:: block.
• No CHANGELOG entries or version bumps (handled at release time).

Tracked internally: SDK-2743

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Note

Medium Risk
New experimental async data-path code affects how flag data and change notifications are delivered; interface change on async delete return type is breaking for custom async stores.

Overview
Adds async FDv1 streaming (AsyncStreamingUpdateProcessor) that consumes SSE put/patch/delete events via AsyncSSEClient, applies updates through the config update sink (or store fallback), and reports VALID / INTERRUPTED / OFF like the sync processor—including owned aiohttp session lifecycle when no SSE factory is injected.

Introduces AsyncDataSourceUpdateSinkImpl for async stores: dependency tracking, data-source status broadcasts, and flag-change notifications on init/applied upsert/delete. AsyncFeatureStore.delete now returns bool (mirroring upsert) so stale version-rejected deletes do not fire spurious flag-change events.

Extracts shared datasource_common (STREAM_ALL_PATH, sink_or_store, parse_path) and wires sync polling and streaming through it. DataSourceStatusProviderImpl accepts a small _DataSourceStatusSource protocol so sync and async sinks share one status provider.

Broad unit coverage for the async sink and streaming processor.

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[cursor]

Init skips store-error status update

Medium Severity

When flag-change listeners are registered, init reads prior store data via all outside the store-error try/except. A failure there propagates without recording a STORE_ERROR or moving status to INTERRUPTED, unlike the sync sink where that read is inside the monitored update path.

 

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[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

There are 2 total unresolved issues (including 1 from previous review).

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[cursor]

Store error kind overwritten

Medium Severity

When the update sink reports STORE_ERROR and re-raises, the streaming processor's broad Exception handler calls update_status again with UNKNOWN. Because a new error is supplied, status is broadcast again and the more specific STORE_ERROR kind is replaced.

Additional Locations (1)

• ldclient/impl/datasource/async_status.py#L41-L47

 

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