Add MessageBufferConfig to allow custom back-pressure config for message.new events

[VelikovPetar]

Goal

Ports V6 PR #6406 (commit 3b6c6546418d010ba4dc29847459bece845bd878) to develop.

Linear issue: AND-1166

Manual port (not a clean cherry-pick) — v7 restructured stream-chat-android-state into stream-chat-android-client and merged StatePluginConfig fields into ChatClientConfig. As a consequence the file paths, packages, and the MessageLimitConfig location all moved:

V6	develop (v7)
stream-chat-android-state module	stream-chat-android-client module
io.getstream.chat.android.state.plugin.config.MessageLimitConfig	io.getstream.chat.android.client.api.MessageLimitConfig
StatePluginConfig.messageLimitConfig	ChatClientConfig.messageLimitConfig

Same intent as the V6 PR — high-traffic channel types (e.g. livestreams) can produce a flood of message.new events that arrive faster than the sequential event-handling pipeline can process them. The current implementation funnels every socket event through a single MutableSharedFlow with extraBufferCapacity = Int.MAX_VALUE, which means there is no back-pressure: a burst of new-message events queues up unbounded memory and starves more important signals (reads, bans, member updates) of timely processing.

This PR introduces a MessageBufferConfig (under MessageLimitConfig.messageBufferConfig) that lets integrators opt specific channel types into a bounded buffer for NewMessageEvents, with a configurable overflow strategy (DROP_OLDEST / DROP_LATEST). Signal-critical events and events for non-opted-in channel types are unaffected. Default is a no-op.

Implementation

• Added MessageBufferConfig (under MessageLimitConfig.messageBufferConfig) exposing:
  • channelTypes: Set<String> — channel types whose NewMessageEvents go through the bounded buffer (empty by default → feature is a no-op).
  • capacity: Int — buffer capacity (defaults to Int.MAX_VALUE).
  • overflow: MessageBufferOverflow — overflow strategy (DROP_OLDEST / DROP_LATEST, defaults to DROP_OLDEST).
• EventHandlerSequential now allocates a secondary MutableSharedFlow (bufferedNewMessageEvents) lazily, only when buffering is enabled, so the default configuration pays no cost for it.
• Two listener variants:
  • defaultSocketEventListener — the existing unbuffered path; used when no channel types are opted in.
  • bufferedSocketEventListener — routes NewMessageEvents for opted-in channel types to the bounded flow, and everything else (including non-opted-in NewMessageEvents and all other event types) to the unbuffered flow.
• startListening() picks the listener based on bufferConfig.channelTypes.isNotEmpty() and only collects from bufferedNewMessageEvents when buffering is enabled.
• StreamStatePluginFactory wires the config from ChatClientConfig.messageLimitConfig.messageBufferConfig into EventHandlerSequential.

The bounded flow shares the same downstream pipeline (socketEventCollector → handleBatchEvent) as the unbuffered flow, so ordering inside each flow is preserved and back-pressure is applied independently per flow.

Files changed (7)

• stream-chat-android-client/api/stream-chat-android-client.api — auto-regenerated via apiDump
• stream-chat-android-client/.../api/ChatClientConfig.kt
• stream-chat-android-client/.../internal/state/event/handler/internal/EventHandlerSequential.kt
• stream-chat-android-client/.../internal/state/plugin/factory/StreamStatePluginFactory.kt
• stream-chat-android-client/.../test/.../internal/state/event/TotalUnreadCountTest.kt
• stream-chat-android-client/.../test/.../internal/state/event/handler/internal/EventHandlerSequentialTest.kt
• stream-chat-android-client/.../test/.../internal/state/event/handler/internal/EventHandlerSequentialUserMessagesDeletedTest.kt

Stats match V6 exactly: +392 / −26.

UI Changes

No UI changes.

Testing

• Added unit tests in EventHandlerSequentialTest covering:
  • NewMessageEvents for opted-in channel types are routed through the bounded buffer.
  • NewMessageEvents for non-opted-in channel types and all non-NewMessageEvent events keep using the unbuffered path.
  • DROP_OLDEST / DROP_LATEST overflow strategies behave as expected when the buffer is full.
  • Bombarding the listener with 5,000 events at capacity 100 drops oldest events under load.
• Existing tests (TotalUnreadCountTest, EventHandlerSequentialUserMessagesDeletedTest) updated to pass the new bufferConfig argument.

Verification on develop:

• detekt ✅
• spotless ✅ (no changes)
• apiDump ✅
• unit tests ✅ (EventHandlerSequentialTest, EventHandlerSequentialUserMessagesDeletedTest, TotalUnreadCountTest, StateRegistryTest)

Summary by CodeRabbit

• New Features
  • Added configurable message buffering for inbound message events by channel type with customizable capacity limits
  • Introduced message overflow strategies to handle capacity limits: drop oldest or drop latest messages when buffer is full
  • Extended message limit configuration to support bounded buffering with flexible overflow handling

[github-actions]

PR checklist ✅

All required conditions are satisfied:

• Title length is OK (or ignored by label).
• At least one pr: label exists.
• Sections ### Goal, ### Implementation, and ### Testing are filled, or the PR is bot-authored.
• An issue is linked (Linear ticket or GitHub issue), or the PR is bot-authored.

🎉 Great job! This PR is ready for review.

[github-actions]

SDK Size Comparison 📏

SDK	Before	After	Difference	Status
stream-chat-android-client	5.83 MB	5.84 MB	0.00 MB	🟢
stream-chat-android-ui-components	11.07 MB	11.07 MB	0.00 MB	🟢
stream-chat-android-compose	12.46 MB	12.46 MB	0.00 MB	🟢

[coderabbitai]

Walkthrough

This PR introduces configurable bounded buffering for socket NewMessageEvents in the Stream chat client. It adds public configuration types (MessageBufferConfig, MessageBufferOverflow), implements buffering logic with overflow strategy selection in EventHandlerSequential, wires configuration through the plugin factory, and validates overflow behavior with new test coverage.

Changes

Message Buffering and Overflow Handling

Layer / File(s)	Summary
Public API contract for buffering configuration stream-chat-android-client/api/stream-chat-android-client.api, stream-chat-android-client/src/main/java/io/getstream/chat/android/client/api/ChatClientConfig.kt	MessageBufferConfig data class exposes channel types, integer capacity, and MessageBufferOverflow strategy. MessageBufferOverflow enum defines DROP_OLDEST and DROP_LATEST overflow strategies. MessageLimitConfig is updated to include messageBufferConfig as a component.
EventHandlerSequential buffering implementation stream-chat-android-client/src/main/java/io/getstream/chat/android/client/internal/state/event/handler/internal/EventHandlerSequential.kt	Constructor accepts bufferConfig parameter. Introduces lazily-created bounded bufferedNewMessageEvents flow that maps MessageBufferOverflow to MutableSharedFlow overflow behavior. Routes socket events conditionally through buffered or default listeners based on channel type configuration. Centralizes emit outcome logging and refactors startListening() to support optional buffering.
Plugin factory configuration wiring stream-chat-android-client/src/main/java/io/getstream/chat/android/client/internal/state/plugin/factory/StreamStatePluginFactory.kt	Extracts messageBufferConfig from ChatClientConfig.messageLimitConfig and passes it through createEventHandler into EventHandlerSequential constructor.
Test infrastructure and buffering behavior validation stream-chat-android-client/src/test/java/io/getstream/chat/android/client/internal/state/event/TotalUnreadCountTest.kt, stream-chat-android-client/src/test/java/io/getstream/chat/android/client/internal/state/event/handler/internal/EventHandlerSequentialTest.kt, stream-chat-android-client/src/test/java/io/getstream/chat/android/client/internal/state/event/handler/internal/EventHandlerSequentialUserMessagesDeletedTest.kt	Test fixtures updated to pass bufferConfig = MessageBufferConfig() into EventHandlerSequential. EventHandlerSequentialTest enhanced with listener capture via AtomicReference, side-effect gating using CompletableDeferred, and new overflow behavior tests validating DROP_OLDEST, DROP_LATEST, non-buffered passthrough, and stress testing with thousands of concurrent NewMessageEvents.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• GetStream/stream-chat-android#6406: Both PRs add the same MessageBufferConfig/overflow wiring to EventHandlerSequential so NewMessageEvent handling uses a lazily-created bounded buffer (with DROP_OLDEST/DROP_LATEST) for configured channel types, and the buffer config is threaded through the respective plugin/factory wiring.

Suggested reviewers

• gpunto

Poem

🐰 Bounded buffers now keep messages in line,
Drop the oldest or newest by your design,
Channel types buffered with care and with grace,
Events flow swiftly through the right place,
Configuration complete, overflow at rest! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 4.35% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description check	✅ Passed	The PR description comprehensively covers Goal, Implementation, Testing, and Files changed sections, thoroughly documenting the feature port, configuration details, and test coverage.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title directly and accurately describes the main change: introducing MessageBufferConfig for back-pressure configuration of message.new events.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch port/v6-to-develop/message-buffer-config

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In
`@stream-chat-android-client/src/main/java/io/getstream/chat/android/client/api/ChatClientConfig.kt`:
- Around line 133-136: Revert MessageLimitConfig to keep the original
primary-constructor shape (single parameter channelMessageLimits) and make
messageBufferConfig an additive property declared in the class body (public val
messageBufferConfig: MessageBufferConfig = MessageBufferConfig()) instead of
adding it to the primary constructor; this preserves the existing generated
one-arg constructor, copy and componentN signatures for binary compatibility
while still exposing the new messageBufferConfig field.
- Around line 218-221: Add an API-level guard to reject non-positive buffer
sizes: in the MessageBufferConfig data class (symbol MessageBufferConfig)
validate the capacity property on construction and throw an
IllegalArgumentException if capacity <= 0 (except when using sentinel values you
intentionally allow), since capacity is used as extraBufferCapacity for
MutableSharedFlow with onBufferOverflow (MessageBufferOverflow) and
MutableSharedFlow requires extraBufferCapacity > 0 for DROP_* policies; ensure
the error message clearly names capacity and MessageBufferConfig so callers see
what's wrong.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: c56d6018-28d0-4d38-a129-e44964a672b9

📥 Commits

Reviewing files that changed from the base of the PR and between 4f2d20b and a9972f1.

📒 Files selected for processing (7)

• stream-chat-android-client/api/stream-chat-android-client.api
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/api/ChatClientConfig.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/internal/state/event/handler/internal/EventHandlerSequential.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/internal/state/plugin/factory/StreamStatePluginFactory.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/internal/state/event/TotalUnreadCountTest.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/internal/state/event/handler/internal/EventHandlerSequentialTest.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/internal/state/event/handler/internal/EventHandlerSequentialUserMessagesDeletedTest.kt

[sonarqubecloud]

Quality Gate failed

Failed conditions
78.6% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud

[stream-public-bot]

🚀 Available in v7.3.0