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

Context:

Python gRPC clients fail with metadata was invalid when calling the online-feature-store service because the py-sdk defines metadata header keys in uppercase. HTTP/2 (RFC 7540 §8.1.2) requires header field names to be lowercase. The Go SDK works because grpc-go auto-lowercases metadata keys, but Python's grpcio enforces the spec strictly and rejects them.

Fixes #165.

Describe your changes:

Lowercased HEADER_CALLER_ID and HEADER_CALLER_TOKEN in py-sdk/grpc_feature_client/grpc_feature_client/client.py:

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

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

These now match the server-side constants in online-feature-store/internal/server/grpc/middleware.go, which the Go SDK was already sending in lowercase form (via grpc-go's auto-normalization).

Testing:

Manual:

Built the py-sdk locally with the patch.
Pointed it at a local online-feature-store instance.
Confirmed that a GetFeatures call now succeeds; without the fix it returns metadata was invalid.

Existing automated tests: the constants are only consumed by the gRPC client header builder, which is exercised by every integration call. No new unit test added — verifying a 2-line constant change is best done at the wire/metadata level which the existing call paths cover.

Monitoring:

No new instrumentation required. Failures previously surfaced as metadata was invalid errors in gRPC client logs; after the fix those errors should no longer occur for Python callers. Existing gRPC server-side metrics for request count / error rate already cover regression detection.

Rollback plan

Single-file, two-line constant change. To revert: git revert <commit-sha> on the merge commit, or change the two constants back to uppercase. No data migrations, no schema changes, no config rollout. Rollback is instant on the next SDK release.

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 (Python gRPC client)

✅ Type of Change

📊 Benchmark / Metrics (if applicable)

N/A — constant value change only, no perf impact.

…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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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 []

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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

coding-shalabh · 2026-05-28T06:46:43Z

Hi @erk1nya — sorry I missed the prior pings. I noticed the earlier "approval" was an automated test and you retracted it. Cleaning house here:

Rewrote the PR description to match the current pull_request_template.md (Testing / Monitoring / Rollback plan sections all filled, plus the standard checklists).
The PR Validation check appears to 404 because it's looking for the branch on Meesho/BharatMLStack instead of the fork coding-shalabh/BharatMLStack:
```
GET /repos/Meesho/BharatMLStack/contents/?ref=fix/py-sdk-grpc-header-case-165 → 404 No commit found
```
That's outside what I can fix from a fork — flagging in case it's a known bot issue with external contributors.

The actual change is a 2-line lowercase fix in py-sdk that unblocks Python gRPC clients (matches what the Go SDK already does via grpc-go's auto-normalization). Could someone do a fresh review when convenient? Thanks!

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

erk1nya approved these changes Mar 20, 2026

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erk1nya reviewed 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 into
Meesho:mainfrom
coding-shalabh:fix/py-sdk-grpc-header-case-165

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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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🔁 Pull Request Template – BharatMLStack

Context:

Describe your changes:

Testing:

Monitoring:

Rollback plan

Checklist before requesting a review

📂 Modules Affected

✅ Type of Change

📊 Benchmark / Metrics (if applicable)

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coding-shalabh commented May 28, 2026

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coding-shalabh commented Mar 16, 2026 •

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