6.2: Implement Streaming for Comments

[justin808]

Overview

Enable RSC streaming for comment loading on story detail pages.

Parent Epic: #70
Priority: P1

Prerequisites

• 4.7: Create Item Detail Page Component #88 (4.7: Create Item Detail Page Component)
• 4.8: Create Comment Component (Recursive) #89 (4.8: Create Comment Component)
• 4.11: Create Loading Skeletons #92 (4.11: Create Loading Skeletons)

Next Issues (after this is complete)

• 7.3: Write Integration Tests (verify streaming behavior)

Acceptance Criteria

• Comments load progressively (don't block story details)
• Deep comment threads handled efficiently
• Suspense boundaries wrap comment tree
• Comment skeletons show during loading
• Story header/details visible before comments load

Implementation Notes

Comments are often the slowest part of HN pages due to:

1. Many nested API calls for child comments
2. Deep recursion in comment trees

Streaming allows the story details to appear immediately while comments load in the background.

Consider wrapping comment tree in Suspense:

<Suspense fallback={<CommentTreeSkeleton />}>
  <CommentTree comments={comments} />
</Suspense>

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Examples

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🔗 Similar & Duplicate Issues

Related Issues

• shakacode/react_on_rails-demos#96
• shakacode/react_on_rails-demos#92
• shakacode/react_on_rails-demos#89
• shakacode/react_on_rails-demos#88
• shakacode/react_on_rails-demos#90

🔗 Related PRs

shakacode/react_on_rails#2015 - Concurrently drain streaming fibers [merged] | react_on_rails_pro/CHANGELOG.md:
"""

AI-generated summary of changes

• Adds two new Unreleased sections: Improved and Added.
• Improved: introduces concurrent processing for streaming React components to replace sequential processing, reducing latency for stream_view_containing_react_components.
• Added: introduces config.concurrent_component_streaming_buffer_size with default 64 to tune memory buffer for concurrent streaming (trade-off between memory usage and performance).
• Added: adds async gem dependency (>= 2.6) to support the new concurrent streaming feature.

"""

---

react_on_rails_pro/lib/react_on_rails_pro/concerns/stream.rb:
"""

AI-generated summary of changes

• Replaces the direct iterative draining of fibers with a concurrent streaming model using Async and a LimitedQueue.
• Introduces drain_streams_concurrently to coordinate producer tasks (build_producer_tasks) and a writer task (build_writer_task) that dequeues chunks and writes them in order.
• Adds memory-bounded buffering via a queue; producers enqueue [index, chunk], writer dequeues and writes, and the queue is closed to signal end-of-stream.
• Moves stream finalization to an ensure block that closes the stream after draining, instead of closing inside the original loop.
• Replaces the in-loop fiber.resume iteration with a multi-task flow: starts producers and writer, waits on producers, then signals end-of-stream and waits for writer.
• Adds private helper methods for building producer tasks and the writer task; each producer resumes fibers and enqueues chunks with their index.
• Introduces explicit end-of-stream signaling via queue.close and handling of nil dequeues by the writer.

Alterations to the declarations of exported or public entities

• None

Estimated code review effort: High

Estimated code review effort: High
"""

---

react_on_rails_pro/lib/react_on_rails_pro/configuration.rb:
"""

AI-generated summary of changes

• Adds a new configuration option concurrent_component_streaming_buffer_size with a default value of 64.
• Exposes concurrent_component_streaming_buffer_size as a public attribute on the Configuration class.
• Extends the Configuration initializer to accept concurrent_component_streaming_buffer_size and stores it on the instance.
• Includes concurrent_component_streaming_buffer_size in the public configuration hash produced by ReactOnRailsPro.configuration.
• Wires concurrent_component_streaming_buffer_size into the initial Configuration.new(...) call.
• Introduces a public method validate_concurrent_component_streaming_buffer_size to enforce that concurrent_component_streaming_buffer_size is a positive numeric value.
• Invokes validate_concurrent_component_streaming_buffer_size during setup_config_values.

Alterations to the declarations of exported or public entities

• Constant added: DEFAULT_CONCURRENT_COMPONENT_STREAMING_BUFFER_SIZE = 64 in class ReactOnRailsPro::Configuration
• Attribute accessor updated: :concurrent_component_streaming_buffer_size in ReactOnRailsPro::Configuration
• Constructor signature updated: include concurrent_component_streaming_buffer_size: in def initialize(...)
• Initialization assignment updated: self.concurrent_component_streaming_buffer_size = concurrent_component_streaming_buffer_size in ReactOnRailsPro::Configuration#initialize
• Public API change: concurrent_component_streaming_buffer_size appears in the configuration hash returned by ReactOnRailsPro.configuration
• Wiring change: pass concurrent_component_streaming_buffer_size in the initial Configuration.new(...) call
• Public method added: validate_concurrent_component_streaming_buffer_size in ReactOnRailsPro::Configuration to validate the new setting
• Validation invocation: call to validate_concurrent_component_streaming_buffer_size inside setup_config_values

Manifest File Analyzer

Estimated code review effort: Medium
"""

---

react_on_rails_pro/lib/react_on_rails_pro/utils.rb:
"""

AI-generated summary of changes

• Updated inline documentation to refer to Shakapacker instead of Webpacker for two methods.
• bundle_file_name now uses ReactOnRails::PackerUtils.bundle_js_uri_from_packer to obtain the path and Pathname.basename for the file name, replacing the previous webpacker-based semantics.
• server_bundle_file_name signature remains unchanged, but its implementation shifts from deriving a hash via a simple wrapper around bundle_file_name to caching via an instance variable and computing the server bundle name through bundle_file_name, centralizing the name resolution.
• Updated comments to reflect “Shakapacker” usage and clarified the purpose of keys (cache keys vs fragment-caching keys) accordingly.
• No observable changes to return values or control flow aside from the moved/renamed processing path and updated comments.

Alterations to the declarations of exported or public entities

• No signature changes detected in exported/public entities.

Estimated code review effort: Medium
"""

---

react_on_rails_pro/react_on_rails_pro.gemspec:
"""

AI-generated summary of changes

Adds a new runtime dependency "async" with version constraint ">= 2.6" to the gemspec, increasing runtime requirements. No other dependencies or metadata are modified; the change is a single addition to s.add_runtime_dependency.

• Method added: s.add_runtime_dependency "async", ">= 2.6" in file react_on_rails_pro/react_on_rails_pro.gemspec

Estimated code review effort: Medium
"""

---

react_on_rails_pro/spec/dummy/spec/helpers/react_on_rails_pro_helper_spec.rb:
"""

AI-generated summary of changes

• Adds Async::Queue-based streaming support to tests by allowing mock_request_and_response to handle both Async::Queue and Array inputs. When a queue is provided, chunks are dequeued in a loop until nil and yielded as before; when an array is provided, behavior remains unchanged.
• Introduces execute_stream_view_containing_react_components as a new test helper that wires an Async queue to mock_request_and_response, drives the streaming flow via stream_view_containing_react_components, enqueues chunks progressively with delays, and asserts that written chunks mirror received chunks during streaming.
• Replaces direct invocations of stream_view_containing_react_components(template: ...) with the new execute_stream_view_containing_react_components helper in multiple tests to drive the Async-based path.
• Extends the stream_view_containing_react_components describe block to use Async::Queue-driven mocks, mirroring the same async-chunk delivery behavior used for streaming tests.
• Keeps existing assertions around chunk writing timing, Rails context and component tagging, and content checks, but adapts control flow to support both synchronous array inputs and asynchronous queue inputs.
• Adds require statements for async and async/queue to enable new Async-based test paths.

Alterations to the declarations of exported or public entities

• None

Estimated code review effort: Major
"""

---

react_on_rails_pro/spec/react_on_rails_pro/stream_spec.rb:
"""

AI-generated summary of changes

• Adds a new StreamController class inside react_on_rails_pro/spec/react_on_rails_pro/stream_spec.rb that includes ReactOnRailsPro::Stream, exposes a public response reader, and implements initialize(component_queues:, initial_response: "TEMPLATE") and render_to_string(**_opts). The render_to_string method sets up per-queue Fibers to yield chunks from Async::Queue instances and returns the initial_response.
• Extends tests with a new "Component streaming concurrency" suite, introducing helpers run_stream and setup_stream_test. The setup mocks ActionController::Live::Response and Buffer, wires controller.response to the mocked response, and configures stream.write/close expectations.
• Adds test scenarios for concurrent streaming, per-component ordering, empty component lists, single components, and backpressure with a slow writer, including assertions on interleaving and timing.
• Duplicates or augments streaming tests across sections to reinforce concurrency behavior and cleanup paths.
• Introduces backpressure and disconnect-handling logic in tests by simulating slow writes and observing write timings and closures.

Alterations to the declarations of exported or public entities

• New class added: StreamController in react_on_rails_pro/spec/react_on_rails_pro/stream_spec.rb
• Public module include added to the new class: include ReactOnRailsPro::Stream
• Public attribute reader added: attr_reader :response in StreamController
• Public method added: def initialize(component_queues:, initial_response: "TEMPLATE") in StreamController
• Public method added: def render_to_string(**_opts) in StreamController
• Public attribute and parameter usage: @component_queues, @initial_response in StreamController initialization
• New test helper methods and test-scoped public-like constructs introduced within the spec (e.g., run_stream, setup_stream_test) to drive public-facing streaming behavior tests
  """

👤 Suggested Assignees

• justin808
• ihabadham

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