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

What type of PR is this?

Description

🔁 Pull Request Template – BharatMLStack

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 grpc auto-lowercases keys, but Python 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 and comply with HTTP/2 header requirements.

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

📊 Benchmark / Metrics (if applicable)

N/A — constant value change only.

Key Requirement Doc

Pod Type:

H0
H1
H2

Why KRD is not required?
This is a one-line bug fix changing constant values from uppercase to lowercase. No architectural or design decisions involved.

Added Tests

👍 yes
🙅 no, because they aren't needed
🙋 no, because I need help

If yes, what is the strategy?

Manual
Unit Tests
API/Integration Tests

Root Cause

The Python SDK defined gRPC metadata headers with uppercase characters:

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

Python grpcio enforces RFC 7540 §8.1.2 strictly: HTTP/2 header names MUST be lowercase. Go grpc-go auto-lowercases metadata keys, so the Go SDK works. Python grpcio does not auto-lowercase and rejects them.

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.

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 test selection made (Yes/No/Need Help!)
KRD link missing — provide a KRD document or check 'KRD is not required'
downstream systems impact not specified

Please fill out the form to fix this: Open Form

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

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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.

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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

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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 •

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

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What type of PR is this?

Description

🔁 Pull Request Template – BharatMLStack

Context:

Describe your changes:

Checklist before requesting a review

📂 Modules Affected

✅ Type of Change

📊 Benchmark / Metrics (if applicable)

Key Requirement Doc

Added Tests

If yes, what is the strategy?

Root Cause

Fix

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PR Validation Failed

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Walkthrough

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coding-shalabh commented Mar 16, 2026 •

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