feat: add ETag/caching support in OFREP by toddbaert · Pull Request #1854 · open-feature/flagd

toddbaert · 2026-01-27T20:37:06Z

Implement caching in bulk evaluations as per OFREP spec.

See: https://openfeature.dev/docs/reference/other-technologies/ofrep/openapi

This is a requirement for deprecating the flagd-web-provider, as without it, polling would be substantially more expensive.

Relates to: open-feature/js-sdk-contrib#1459

netlify · 2026-01-27T20:37:14Z

✅ Deploy Preview for polite-licorice-3db33c canceled.

Name	Link
🔨 Latest commit	`ae50fdb`
🔍 Latest deploy log	https://app.netlify.com/projects/polite-licorice-3db33c/deploys/697921f6d7f4c100082db7c3

netlify · 2026-01-27T20:37:14Z

✅ Deploy Preview for polite-licorice-3db33c ready!

Name	Link
🔨 Latest commit	`73f07a4`
🔍 Latest deploy log	https://app.netlify.com/projects/polite-licorice-3db33c/deploys/697bb94e399f0e000791c808
😎 Deploy Preview	https://deploy-preview-1854--polite-licorice-3db33c.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

To edit notification comments on pull requests, go to your Netlify project configuration.

gemini-code-assist · 2026-01-27T20:37:24Z

Summary of Changes

Hello @toddbaert, 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 robust caching capabilities to the OFREP bulk evaluation endpoint by implementing HTTP ETag support. This enhancement significantly optimizes performance for clients, particularly those using polling mechanisms, by preventing redundant data transfers when flag configurations remain unchanged. It's a critical step towards deprecating the flagd-web-provider by ensuring efficient data handling.

Highlights

ETag/Caching Support for OFREP Bulk Evaluations: Implemented ETag-based caching for bulk evaluation responses in the OpenFeature Remote Evaluation Protocol (OFREP) service. This allows clients to cache responses and receive 304 Not Modified status codes if the content has not changed, reducing network traffic and improving performance.
New HTTP Header Constants: Introduced new constants for HTTP headers such as ETag, If-None-Match, Content-Type, and application/json to standardize their usage.
ETag Calculation Logic: Added a calculateETag helper function that computes a SHA256 hash of the JSON response body to generate a unique ETag for each bulk evaluation response.
Bulk Evaluation Response Handling: Refactored the HandleBulkEvaluation method to utilize a new writeBulkEvaluationResponse function, which encapsulates the ETag generation, If-None-Match header validation, and conditional response sending (either 200 OK with content or 304 Not Modified).
Comprehensive Unit Tests: Added extensive unit tests for the new ETag functionality, covering scenarios for writeBulkEvaluationResponse (no If-None-Match, matching ETag, non-matching ETag) and calculateETag (valid response, empty response, deterministic output).

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	`/gemini review`	Performs a code review for the current pull request in its current state.
Pull Request Summary	`/gemini summary`	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	`/gemini help`	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

gemini-code-assist

Code Review

This pull request adds ETag-based caching to the OFREP bulk evaluation endpoint, which is a great feature for improving performance and reducing server load. The implementation is solid and includes good test coverage. I've provided a few suggestions to further improve performance by avoiding redundant JSON marshaling and to enhance logging by using structured fields, which will improve maintainability.

flagd/pkg/service/flag-evaluation/ofrep/handler.go

leakonvalinka · 2026-01-28T10:34:16Z

flagd/pkg/service/flag-evaluation/ofrep/handler.go

+}
+
+// calculateETag generates an ETag from the bulk evaluation response
+func calculateETag(response ofrep.BulkEvaluationResponse) (string, []byte, error) {


Q: For the ETag calculation the flags must be in the same order every time, is this guaranteed?

Great point!

Ordering in maps in Go is intentionally non-deterministic so that devs cannot rely on it, but the JSON marshalling in Go does sort them:

https://github.com/golang/go/blob/master/src/encoding/json/encode.go#L183-L189

So we can rely on that.

Okay good to know, thank you!

TIL as well (the json marshall ordering bit). I know maps were purposely random in Go, so I was quite scared for a second.

erka

Overall it looks great. I’m not sure whether SHA-256 is really required here, and it could add extra CPU load. SHA-1 or xxHash might be just as good for this use case.

toddbaert · 2026-01-28T13:47:12Z

Overall it looks great. I’m not sure whether SHA-256 is really required here, and it could add extra CPU load. SHA-1 or xxHash might be just as good for this use case.

I went back and forth on this as well. SHA-1 was my first thought. It's not spec'd or anything so we could change it later... I will go back to sha1 and save some CPU cycles.

toddbaert · 2026-01-28T13:52:18Z

Overall it looks great. I’m not sure whether SHA-256 is really required here, and it could add extra CPU load. SHA-1 or xxHash might be just as good for this use case.

I went back and forth on this as well. SHA-1 was my first thought. It's not spec'd or anything so we could change it later... I will go back to sha1 and save some CPU cycles.

Did this and also added some minor docs.

docs/reference/flagd-ofrep.md

flagd/pkg/service/flag-evaluation/ofrep/handler.go

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

Co-authored-by: Roman Dmytrenko <rdmytrenko@gmail.com> Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

sonarqubecloud · 2026-01-29T19:50:00Z

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

toddbaert · 2026-01-30T17:16:43Z

Hey @erka @jonathannorris @jonathannorris @leakonvalinka If you have time, take a look at this alternative, which does something more like @jonathannorris suggested: #1858

toddbaert requested review from a team as code owners January 27, 2026 20:37

dosubot bot added the size:L This PR changes 100-499 lines, ignoring generated files. label Jan 27, 2026

toddbaert requested review from alexandraoberaigner, beeme1mr, jonathannorris and marcozabel January 27, 2026 20:37

gemini-code-assist bot reviewed Jan 27, 2026

View reviewed changes

flagd/pkg/service/flag-evaluation/ofrep/handler.go Show resolved Hide resolved

flagd/pkg/service/flag-evaluation/ofrep/handler.go Outdated Show resolved Hide resolved

flagd/pkg/service/flag-evaluation/ofrep/handler.go Outdated Show resolved Hide resolved

toddbaert mentioned this pull request Jan 27, 2026

feat: deprecate flagd-web provider open-feature/js-sdk-contrib#1459

Draft

marcozabel approved these changes Jan 27, 2026

View reviewed changes

erka reviewed Jan 27, 2026

View reviewed changes

flagd/pkg/service/flag-evaluation/ofrep/handler.go Outdated Show resolved Hide resolved

leakonvalinka reviewed Jan 28, 2026

View reviewed changes

toddbaert requested review from erka and leakonvalinka January 28, 2026 12:48

erka approved these changes Jan 28, 2026

View reviewed changes

jonathannorris reviewed Jan 29, 2026

View reviewed changes

docs/reference/flagd-ofrep.md Outdated Show resolved Hide resolved

jonathannorris reviewed Jan 29, 2026

View reviewed changes

flagd/pkg/service/flag-evaluation/ofrep/handler.go Show resolved Hide resolved

toddbaert requested a review from jonathannorris January 29, 2026 17:51

toddbaert and others added 6 commits January 29, 2026 14:47

feat: add ETag/caching support in OFREP

46db024

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

fixup: gemini recommendations for avoiding more marshalling

d6b50a5

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

Update flagd/pkg/service/flag-evaluation/ofrep/handler.go

bfa8a17

Co-authored-by: Roman Dmytrenko <rdmytrenko@gmail.com> Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

fixup: unused import

f1b017f

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

fixup: sha1, and docs

567fcbb

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

fixup: use md5

73f07a4

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

toddbaert force-pushed the feat/ofrep-caching branch from 1c64261 to 73f07a4 Compare January 29, 2026 19:47

toddbaert marked this pull request as draft January 30, 2026 14:07

leakonvalinka approved these changes Jan 30, 2026

View reviewed changes

toddbaert mentioned this pull request Jan 30, 2026

feat: cross-replica, OFREP bulk evaluation caching #1858

Open

Conversation

toddbaert commented Jan 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

netlify bot commented Jan 27, 2026

✅ Deploy Preview for polite-licorice-3db33c canceled.

Uh oh!

netlify bot commented Jan 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

✅ Deploy Preview for polite-licorice-3db33c ready!

Uh oh!

gemini-code-assist bot commented Jan 27, 2026

Summary of Changes

Highlights

Footnotes

Uh oh!

gemini-code-assist bot left a comment

Choose a reason for hiding this comment

Code Review

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

leakonvalinka Jan 28, 2026

Choose a reason for hiding this comment

Uh oh!

toddbaert Jan 28, 2026

Choose a reason for hiding this comment

Uh oh!

leakonvalinka Jan 28, 2026

Choose a reason for hiding this comment

Uh oh!

toddbaert Jan 28, 2026

Choose a reason for hiding this comment

Uh oh!

erka left a comment

Choose a reason for hiding this comment

Uh oh!

toddbaert commented Jan 28, 2026

Uh oh!

toddbaert commented Jan 28, 2026

Uh oh!

Uh oh!

Uh oh!

sonarqubecloud bot commented Jan 29, 2026

Quality Gate passed

Uh oh!

toddbaert commented Jan 30, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

toddbaert commented Jan 27, 2026 •

edited

Loading

netlify bot commented Jan 27, 2026 •

edited

Loading