Stream Gemini Summary Response by trett · Pull Request #142 · trett/rssreader

trett · 2026-02-12T19:01:58Z

This PR introduces streaming summary generation using Gemini's API.

Key Changes:

Backend: Refactored to stream content using Gemini's streaming API.
API: Updated to return Server-Sent Events (SSE).
Frontend: Updated to consume the SSE stream and update the UI incrementally.
Dependencies: Added for streaming JSON parsing.

This change significantly improves the user experience by displaying the summary as it is generated, reducing the perceived waiting time.

gemini-code-assist · 2026-02-12T19:02:18Z

Summary of Changes

Hello @trett, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a fundamental shift in how AI summaries are delivered to the user, moving from a batch-processing model to a real-time streaming approach. By leveraging Gemini's streaming capabilities and Server-Sent Events, the system can now progressively render summary content, metadata, and fun facts, providing a more dynamic and responsive user interface. This enhancement aims to make the summary generation process feel faster and more interactive for the end-user.

Highlights

Streaming Summary Generation: The application now generates summaries using Gemini's streaming API, allowing for incremental display of content.
API Update to Server-Sent Events (SSE): The backend API endpoint for summaries has been updated to return Server-Sent Events, enabling real-time updates to the client.
Frontend Integration of SSE: The frontend has been modified to consume the SSE stream, updating the UI incrementally as summary content is received.
Dependency Addition: The circe-fs2 library was added to handle streaming JSON parsing on the server side.
Improved User Experience: This change significantly reduces perceived waiting time by displaying summaries as they are generated, enhancing the user experience.

Changelog

build.sbt
- Updated the project version to 2.4.3.
- Added io.circe:circe-fs2 dependency for streaming JSON parsing.
client/src/main/scala/client/Models.scala
- Added Decoder instances for various SummaryEvent types (Content, Metadata, FunFact, Error, Done) to handle streamed data.
client/src/main/scala/client/NetworkUtils.scala
- Imported SummaryEvent.
- Introduced a new streamSummary function that establishes an EventSource connection to receive Server-Sent Events and emits them via an EventBus.
client/src/main/scala/client/SummaryPage.scala
- Removed imports for SummaryResponse, SummarySuccess, SummaryError and Try.
- Replaced the batch-fetching fetchSummaryBatch and batchObserver with startStreaming and cleanup functions.
- Implemented logic to manage EventSource subscriptions and incrementally update the UI based on SummaryEvent types (Content, Metadata, FunFact, Error, Done).
scripts/local-docker/docker-compose.yml
- Updated the server image version to server:2.4.3.
server/src/main/scala/ru/trett/rss/server/codecs/SummaryCodecs.scala
- Imported SummaryEvent.
- Added Encoder instances for SummaryEvent types (Content, Metadata, FunFact, Error, Done) to serialize them for SSE.
server/src/main/scala/ru/trett/rss/server/controllers/SummarizeController.scala
- Replaced CirceEntityEncoder import with ServerSentEvent and io.circe.syntax.
- Modified the /api/summarize endpoint to return a Stream[IO, ServerSentEvent] by mapping SummaryEvent instances to ServerSentEvent.
server/src/main/scala/ru/trett/rss/server/services/SummarizeService.scala
- Imported fs2.Stream.
- Updated imports to use SummaryEvent instead of SummaryResponse, SummaryResult, SummarySuccess, and SummaryError.
- Modified getEndpoint to include a stream parameter, allowing selection between generateContent and streamGenerateContent.
- Added a stream parameter to buildGeminiRequest to enable streaming requests.
- Replaced the getSummary method with streamSummary, which now returns an fs2.Stream[IO, SummaryEvent].
- Refactored the summary generation logic within streamSummary to emit SummaryEvent instances (Metadata, FunFact, Content, Error, Done) as a stream.
- Changed summarize to summarizeStream, which now builds a streaming Gemini request and processes the response body as a stream of GeminiResponse objects, mapping them to SummaryEvent.Content.
shared/src/main/scala/ru/trett/rss/models/SummaryEvent.scala
- Added a new file defining the SummaryEvent sealed trait and its case classes: Content, Metadata, FunFact, Error, and Done.

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Code Review

This pull request is a significant improvement, refactoring the summary generation to use a streaming approach with Gemini's API and Server-Sent Events. The changes on the backend, API, and frontend are well-executed and will greatly enhance the user experience by providing incremental updates. I've identified a couple of areas for improvement in the backend service to increase robustness, particularly around error handling and response parsing in the new streaming logic.

server/src/main/scala/ru/trett/rss/server/services/SummarizeService.scala

trett · 2026-02-14T18:11:25Z

/gemini review

gemini-code-assist

Code Review

This pull request successfully refactors summary generation to a streaming model using Gemini's API and Server-Sent Events, significantly enhancing the user experience by displaying summaries incrementally. However, it introduces security vulnerabilities related to LLM input/output handling. Specifically, the direct concatenation of untrusted RSS feed content into prompts allows for prompt injection, and the unsafe rendering of LLM-generated HTML on the client side leads to Cross-Site Scripting (XSS). These security concerns should be addressed by implementing client-side HTML sanitization and more secure prompt construction techniques. Additionally, there are suggestions to improve error handling and response parsing on the backend.

client/src/main/scala/client/SummaryPage.scala

server/src/main/scala/ru/trett/rss/server/services/SummarizeService.scala

gemini-code-assist · 2026-02-14T18:13:03Z

server/src/main/scala/ru/trett/rss/server/services/SummarizeService.scala

                            .map { geminiResp =>
                                geminiResp.candidates.headOption
                                    .flatMap(_.content.parts.flatMap(_.headOption))
-                                    .map(_.text)
-                                    .map { text =>
-                                        if text.startsWith("```html") then
-                                            text.stripPrefix("```html").stripSuffix("```").trim
-                                        else text.trim
-                                    } match
-                                    case Some(html) if html.nonEmpty => SummarySuccess(html)
-                                    case _ =>
-                                        SummaryError("Could not extract summary from response.")
+                                    .map(_.text.replace("```html", "").replace("```", ""))
+                                    .getOrElse("")
                            }
+                            .map(SummaryEvent.Content(_))


Using .replace() to strip markdown fences is a bit too broad and could corrupt the generated HTML if the fence characters appear within the content itself. The previous, non-streaming implementation's use of stripPrefix and stripSuffix is safer as it only targets the beginning and end of the string.

Additionally, filtering out empty content chunks would be a good practice to avoid sending unnecessary events to the client.

.map { geminiResp => geminiResp.candidates.headOption .flatMap(_.content.parts.flatMap(_.headOption)) .map(_.text) .getOrElse("") } .map { text => if (text.startsWith("```html")) { text.stripPrefix("```html").stripSuffix("```").trim } else { text.trim } } .filter(_.nonEmpty) .map(SummaryEvent.Content(_))

…ervice

trett · 2026-02-14T18:40:35Z

Applied the suggested fix for markdown stripping and empty chunk filtering.

trett · 2026-02-14T18:41:09Z

I have addressed the unresolved comment regarding markdown stripping and empty chunk filtering. The changes have been pushed to the branch.

trett · 2026-02-14T18:54:01Z

Ran scalafix and scalafmt. Refactored SummaryPage.scala to remove mutable state and improve stream lifecycle management.

…EventSource - Replace onMountCallback with EventStream.merge to guarantee initial request in SummaryPage - Use ListBuffer in NetworkUtils to properly track and close EventSource connections - Update AGENTS.md to enforce scalafix/scalafmt usage

streaming response

e72b6d5

gemini-code-assist bot reviewed Feb 12, 2026

View reviewed changes

trett added 2 commits February 14, 2026 19:02

Refactor SummaryPage using Scala.js and Laminar best practices

55e6675

Fix robust HTML stripping for streaming response

8ae6457

trett commented Feb 14, 2026

View reviewed changes

server/src/main/scala/ru/trett/rss/server/services/SummarizeService.scala Show resolved Hide resolved

Make summarizeStream self-contained by ensuring Done event on all paths

d744a78

trett commented Feb 14, 2026

View reviewed changes

server/src/main/scala/ru/trett/rss/server/services/SummarizeService.scala Show resolved Hide resolved

gemini-code-assist bot reviewed Feb 14, 2026

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fix: Improve markdown stripping and filter empty chunks in SummarizeS…

79e628c

…ervice

trett added 2 commits February 14, 2026 21:06

style: apply scalafmt formatting to SummarizeService

13c48e4

trett force-pushed the stream-reposponse branch from fa9f38f to 13c48e4 Compare February 14, 2026 20:07

clear source

8b5a35a

trett merged commit c0eff9b into main Feb 15, 2026
1 check passed

trett deleted the stream-reposponse branch February 15, 2026 12:01

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Stream Gemini Summary Response#142

Stream Gemini Summary Response#142
trett merged 8 commits intomainfrom
stream-reposponse

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