Streaming support #365

Tymek · 2025-08-12T16:43:06Z

Description

Added streaming support.

Fixes internal issue CTO-249

Type of change

Please delete options that are not relevant.

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to not work as expected)
This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

Unit tests
Spec Tests
Integration tests / Manual Tests

Checklist:

My code follows the style guidelines of this project
I have performed a self-review of my own code
I have commented my code, particularly in hard-to-understand areas
I have made corresponding changes to the documentation
My changes generate no new warnings
I have added tests that prove my fix is effective or that my feature works
New and existing unit tests pass locally with my changes
Any dependent changes have been merged and published in downstream modules

Tymek · 2025-08-19T14:19:01Z

UnleashClient/__init__.py

+                    else:
+                        # MODE: offline
+
+                        job_args = base_job_args
+                        job_func = load_features


Python SDK sets up periodic update on bootstrapped toggles. I don't think this is consistent across SDKs

coveralls · 2025-08-19T17:07:33Z

Pull Request Test Coverage Report for Build 17217536564

Details

112 of 134 (83.58%) changed or added relevant lines in 5 files are covered.
No unchanged relevant lines lost coverage.
Overall coverage decreased (-2.6%) to 92.397%

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
UnleashClient/init.py	24	28	85.71%
UnleashClient/streaming/event_processor.py	33	37	89.19%
UnleashClient/streaming/connector.py	51	65	78.46%

Totals
Change from base Build 16809197061:	-2.6%
Covered Lines:	559
Relevant Lines:	605

💛 - Coveralls

kwasniew

do we have any unit or integration tests showing how streaming works?

UnleashClient/__init__.py

UnleashClient/streaming/manager.py

…ingEventProcessor

for more information, see https://pre-commit.ci

kwasniew

I still don't see any tests

kwasniew · 2025-08-22T07:38:26Z

UnleashClient/__init__.py

@@ -111,7 +113,7 @@ class UnleashClient:
    :param event_callback: Function to call if impression events are enabled.  WARNING: Depending on your event library, this may have performance implications!
    """

-    def __init__(
+    def __init__(  # noqa: PLR0915


why was it added?

"too many statements" linting exception

kwasniew · 2025-08-22T07:49:21Z

UnleashClient/__init__.py

@@ -136,6 +138,8 @@ def __init__(
        scheduler_executor: Optional[str] = None,


In Ruby we managed to re-use fetcher_scheduled_executor that is either polling toggle fetcher or streaming. Check usage of https://github.com/Unleash/unleash-ruby-sdk/blob/main/lib/unleash/client.rb#L14 for details. @sighphyre started a great discussion about it here https://github.com/Unleash/unleash-ruby-sdk/pull/248/files#r2262867667. Since Python is similar to Ruby it should be doable too. In Java it was too difficult. In Node I will try to migrate towards this approach too in a subsequent PR.

kwasniew · 2025-08-22T07:54:06Z

UnleashClient/__init__.py

@@ -169,6 +173,9 @@ def __init__(
        self.unleash_verbose_log_level = verbose_log_level
        self.unleash_event_callback = event_callback
        self._ready_callback = build_ready_callback(event_callback)
+        self.experimental_mode = experimental_mode


I don't like the fact that we have explosion of fields that work for either polling or streaming. In clear OO design we'd have swappable mechanism for one fetching strategy at a time. I know in Java and .NET we also mix but I plan to fix this in Node. Maybe worth investigating this option in Python?

UnleashClient/streaming/event_processor.py

kwasniew · 2025-08-22T08:40:14Z

UnleashClient/streaming/connector.py

+        self._headers = {**headers, "Accept": "text/event-stream"}
+        self._timeout = request_timeout
+        self._on_ready = on_ready
+        self._sse_factory = sse_client_factory


creating testability/swapping option is only valuable if you gonnd use this option. From my review it looks like we exposed this option (increased complexity) but we never exercised this option. I think in the production implementation of a connector.py we only need to wrap LD client. More detail why too much dependency inversion can be harmful: https://dannorth.net/blog/cupid-the-back-story/#dependency-inversion-principle

kwasniew · 2025-08-22T08:46:11Z

tests/unit_tests/streaming/test_client_streaming.py

+        self.data = data
+
+
+class FiniteSSEClient:


The current approach with FiniteSSEClient and factory pattern is:

More isolated (unit test style)

Faster but less realistic

Requires production code changes (factory parameter)

Network-level testing (check Java and Ruby, Node is not doing this) would be more realistic because:

Tests the actual SSE client library behavior

Verifies correct handling of SSE format

Catches integration issues

More confidence in production behavior

This code uses responses library for polling mode tests.
It could theoretically mock SSE responses

ruby example: https://github.com/Unleash/unleash-ruby-sdk/pull/248/files#diff-9f5de0ba29bb75d4bbc376507bb2ecbde605866a7a2bfcdf550c370298ae8f54R766

UnleashClient/streaming/connector.py

Tymek · 2025-08-25T10:26:59Z

UnleashClient/__init__.py

+                        job_args = {
+                            **base_job_args,
+                            "url": self.unleash_url,
+                            "app_name": self.unleash_app_name,
+                            "instance_id": self.unleash_instance_id,
+                            "headers": {
+                                **base_headers,
+                                "unleash-interval": self.unleash_refresh_interval_str_millis,
+                            },
+                            "custom_options": self.unleash_custom_options,
+                            "request_timeout": self.unleash_request_timeout,
+                            "request_retries": self.unleash_request_retries,
+                            "event_callback": self.unleash_event_callback,
+                            "project": self.unleash_project_name,
+                        }
+
+                        job_func: Callable
+                        job_func = fetch_and_load_features


My goal here was to avoid larger refactor. I'd like to extract 'mode' (fetching strategy / connector) into a separate layer, but in this SDK fetching runs on the same 'scheduler' as metrics. Decoupling this should be done in another PR in my opinion.

initial streaming support

fe6832e

thomasheartman added this to Issues and PRs Aug 12, 2025

github-project-automation bot moved this to New in Issues and PRs Aug 12, 2025

Tymek added 3 commits August 12, 2025 19:03

streaming example

db0a837

delta polling

86dd667

formatting

f2eab4f

Tymek force-pushed the feat/streaming branch from 0252e92 to f2eab4f Compare August 12, 2025 17:09

update example

b25e820

Tymek force-pushed the feat/streaming branch from ee3f641 to b25e820 Compare August 12, 2025 17:17

gastonfournier moved this from New to In Progress in Issues and PRs Aug 13, 2025

Tymek added 3 commits August 19, 2025 11:00

refactor: consolidate job arguments

5c5e542

refactor: simplify mode selection

f7596b7

refactor: update mode selection logic

394ac5f

Tymek commented Aug 19, 2025

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Tymek added 3 commits August 19, 2025 17:01

refactor: enhance job scheduling logic for streaming and polling modes

6bbc162

fix: lint errors

fecb283

fix: update client specification version to 5.2.2

9ffc01a

chore: remove streaming example and its dependencies

c4ffef3

Tymek force-pushed the feat/streaming branch from 2bba842 to c4ffef3 Compare August 19, 2025 17:08

Tymek requested a review from kwasniew August 19, 2025 17:37

Tymek marked this pull request as ready for review August 20, 2025 07:47

update yggdrasil

2cafba5

kwasniew reviewed Aug 20, 2025

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kwasniew reviewed Aug 20, 2025

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kwasniew reviewed Aug 20, 2025

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Tymek added 3 commits August 20, 2025 14:04

fix: polling

ac8ce42

remove delta-polling

23be09e

refactor: replace StreamingManager with StreamingConnector and Stream…

2072ab4

…ingEventProcessor

Tymek and others added 2 commits August 21, 2025 11:15

fix: add retry strategies and error handling

d6b0293

[pre-commit.ci] auto fixes from pre-commit.com hooks

2beb595

for more information, see https://pre-commit.ci

Tymek requested a review from kwasniew August 21, 2025 09:29

kwasniew reviewed Aug 21, 2025

View reviewed changes

Tymek added 2 commits August 21, 2025 14:50

add tests

3e4500b

lint

a76d913

Tymek force-pushed the feat/streaming branch 2 times, most recently from 9f44f35 to 364a973 Compare August 21, 2025 14:43

Tymek requested a review from kwasniew August 21, 2025 14:44

refactor tests

3cf0222

Tymek force-pushed the feat/streaming branch from 364a973 to 3cf0222 Compare August 21, 2025 14:54

kwasniew reviewed Aug 22, 2025

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kwasniew reviewed Aug 22, 2025

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kwasniew reviewed Aug 22, 2025

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remove heartbeat

f626b57

Tymek force-pushed the feat/streaming branch from 96d811c to f626b57 Compare August 25, 2025 09:20

add TODO for backup file in event processing

4fcfce9

Tymek commented Aug 25, 2025

View reviewed changes

Tymek requested a review from sighphyre August 25, 2025 18:35

		@@ -136,6 +138,8 @@ def __init__(
		scheduler_executor: Optional[str] = None,

Streaming support #365

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Streaming support #365

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Tymek commented Aug 12, 2025 •

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coveralls commented Aug 19, 2025 •

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