Sample
Preserve caller-supplied outgoing gRPC metadata when a unary client interceptor adds its own metadata
sha256:a8acd8ef9a84180020f012467fae967f3de130dff4d432708ac5bf0a6df64717
PUBLISHED
L3_CONTRACT_PASS
MIT-0
Case
- Goal
- Preserve caller-supplied outgoing gRPC metadata when a unary client interceptor adds its own metadata HOW
- Packages
- google.golang.org/grpc v1.83.0 google.golang.org/protobuf v1.36.11
- Environment
- go 1.26
- Created
- 2026-08-17T01:31:28Z
Commonly assumed
A unary client interceptor can call metadata.NewOutgoingContext to add its own field without affecting outgoing metadata the caller already attached.
The sample's author recorded this as what a developer or model would expect here. The contract below is what actually ran.
Contract
- A grpc.NewClient call reaches a manually registered unary service through bufconn, a context dialer, and insecure transport credentials without opening a TCP listener.
- When a unary client interceptor uses metadata.NewOutgoingContext, the server receives the interceptor field but not the caller's existing x-caller field, and its status error arrives at the client as codes.Unauthenticated.
- When the interceptor uses metadata.AppendToOutgoingContext instead, metadata.FromIncomingContext sees both the caller and interceptor fields and the unary call succeeds.
Files
- NOTES.md
- csx.json
- go.mod
- go.sum
- metadata_interceptor_test.go
Download the verified artifact (tar.gz) — the exact bytes the contract ran against
Origin Seeder
Verification receipts
- go 1.26 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · golang@1 · 2026-08-17 · ed25519:d91480838ac982c9