fix(py-sdk): lowercase gRPC metadata headers for Python compatibility by coding-shalabh · Pull Request #359 · Meesho/BharatMLStack

coding-shalabh · 2026-03-16T17:45:01Z

🔁 Pull Request Template – BharatMLStack

Please fill out the following sections to help us review your changes efficiently.

Context:

Python gRPC clients fail with metadata was invalid error because header keys use uppercase characters, which violates HTTP/2 spec (RFC 7540 §8.1.2). Go's grpc auto-lowercases keys, but Python's grpcio rejects them.

Describe your changes:

Lowercased HEADER_CALLER_ID and HEADER_CALLER_TOKEN constants in py-sdk/grpc_feature_client/grpc_feature_client/client.py to match the Go server middleware expectations.

Testing:

Verified header values match Go server middleware constants in middleware.go. The fix is a constant value change — no logic changes.

Monitoring:

NA

Rollback plan

Revert the two constant values back to uppercase.

Checklist before requesting a review

I have reviewed my own changes?
Relevant or critical functionality is covered by tests?
Monitoring needs have been evaluated?
Any necessary documentation updates have been considered?

📂 Modules Affected

horizon (Real-time systems / networking)
online-feature-store (Feature serving infra)
trufflebox-ui (Admin panel / UI)
infra (Docker, CI/CD, GCP/AWS setup)
docs (Documentation updates)
Other: py-sdk

✅ Type of Change

Root Cause

The Python SDK defined headers as:

HEADER_CALLER_ID = "ONLINE-FEATURE-STORE-CALLER-ID"
HEADER_CALLER_TOKEN = "ONLINE-FEATURE-STORE-AUTH-TOKEN"

Python grpcio enforces RFC 7540 §8.1.2: header field names MUST be lowercase in HTTP/2. Go's grpc-go auto-lowercases metadata keys before sending, so the Go SDK works with uppercase constants. Python's grpcio does not — it raises:

Illegal header key
metadata was invalid: [('ONLINE-FEATURE-STORE-CALLER-ID', 'demo'), ...]

Fix

HEADER_CALLER_ID = "online-feature-store-caller-id"
HEADER_CALLER_TOKEN = "online-feature-store-auth-token"

These match the server-side constants in online-feature-store/internal/server/grpc/middleware.go:

callerIdHeader  = "online-feature-store-caller-id"
AuthTokenHeader = "online-feature-store-auth-token"

Fixes #165

…lity Python grpcio rejects metadata keys containing uppercase characters (HTTP/2 spec requires lowercase). The Go SDK works because Go's grpc library auto-lowercases keys, but Python's grpcio does not. Changed HEADER_CALLER_ID and HEADER_CALLER_TOKEN to lowercase to match the Go server middleware expectations in middleware.go. Fixes Meesho#165

readytoreview · 2026-03-16T17:45:08Z

PR Validation Failed

PR description validation failed

Issues found:

no PR type selected
no test selection made (Yes/No/Need Help!)
downstream systems impact not specified

Please fill out the form to fix this: Open Form

turbo-turtle-github · 2026-03-16T17:45:21Z

⚠️ CI Workflow did not complete successfully ⚠️

Links:
No additional links available.

Reason:

IsCICDConfigFilesPresentActivity: GET https://api.github.com/repos/Meesho/BharatMLStack/contents/?ref=fix%2Fpy-sdk-grpc-header-case-165: 404 No commit found for the ref fix/py-sdk-grpc-header-case-165 []

📘 Please check the Turbo Turtle FAQs for more details.

👉 If the reason is not self-explanatory or not covered in the FAQ, please reach out to @devops-oncall in the #devops-tech channel.

coderabbitai · 2026-03-16T17:45:24Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 9235751a-2955-461c-b1a4-c596592c065b

📥 Commits

Reviewing files that changed from the base of the PR and between aec2c74 and 00b5892.

📒 Files selected for processing (1)

py-sdk/grpc_feature_client/grpc_feature_client/client.py

Walkthrough

Updated gRPC authentication header constants from uppercase to lowercase format in the Python gRPC feature client. The changes modify two public header constants to use lowercase ASCII characters, aligning with HTTP/2 metadata requirements enforced by Python gRPC.

Changes

Cohort / File(s)	Summary
gRPC Header Constants `py-sdk/grpc_feature_client/grpc_feature_client/client.py`	Updated `HEADER_CALLER_ID` and `HEADER_CALLER_TOKEN` from uppercase to lowercase format to comply with Python gRPC HTTP/2 metadata validation requirements.

Assessment against linked issues

Objective	Addressed	Explanation
Resolve metadata validation errors in Python gRPC client [`#165`]	✅
Update header keys to lowercase ASCII format [`#165`]	✅

Suggested labels

coderabbit-bugfix

🚥 Pre-merge checks | ✅ 1

✅ Passed checks (1 passed)

Check name	Status	Explanation
Dynamic Configuration Validation	✅ Passed	PR modified only Python SDK source code header constants, with no changes to application-dyn-*.yml configuration files.

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

📝 Coding Plan

Generate coding plan for human review comments

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

Tip

CodeRabbit can scan for known vulnerabilities in your dependencies using OSV Scanner.

OSV Scanner will automatically detect and report security vulnerabilities in your project's dependencies. No additional configuration is required.

erk1nya

LGTM

erk1nya

Disregard previous approval - was automated test

coderabbitai bot added the coderabbit-bugfix label Mar 16, 2026

erk1nya approved these changes Mar 20, 2026

View reviewed changes

erk1nya reviewed Mar 20, 2026

View reviewed changes

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

fix(py-sdk): lowercase gRPC metadata headers for Python compatibility#359

fix(py-sdk): lowercase gRPC metadata headers for Python compatibility#359
coding-shalabh wants to merge 1 commit intoMeesho:mainfrom
coding-shalabh:fix/py-sdk-grpc-header-case-165

coding-shalabh commented Mar 16, 2026 •

edited

Loading

Uh oh!

readytoreview bot commented Mar 16, 2026

Uh oh!

turbo-turtle-github bot commented Mar 16, 2026 •

edited

Loading

Uh oh!

coderabbitai bot commented Mar 16, 2026 •

edited

Loading

Uh oh!

erk1nya left a comment

Uh oh!

erk1nya left a comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Conversation

coding-shalabh commented Mar 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

🔁 Pull Request Template – BharatMLStack

Context:

Describe your changes:

Testing:

Monitoring:

Rollback plan

Checklist before requesting a review

📂 Modules Affected

✅ Type of Change

Root Cause

Fix

Uh oh!

readytoreview bot commented Mar 16, 2026

PR Validation Failed

Uh oh!

turbo-turtle-github bot commented Mar 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

coderabbitai bot commented Mar 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Walkthrough

Changes

Assessment against linked issues

Suggested labels

Uh oh!

erk1nya left a comment

Choose a reason for hiding this comment

Uh oh!

erk1nya left a comment

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

coding-shalabh commented Mar 16, 2026 •

edited

Loading

turbo-turtle-github bot commented Mar 16, 2026 •

edited

Loading

coderabbitai bot commented Mar 16, 2026 •

edited

Loading