Cannot return HTTP header using "Grpc-Metadata-" prefix

[joelurraco]

I have been using the following line of code to return HTTP headers in the server response:

import (
    "google.golang.org/grpc"
    "google.golang.org/grpc/metadata"
)

grpc.SetHeader(ctx, metadata.Pairs("Grpc-Metadata-Some-Key", someValue))

This was working OK using the runtime.DefaultHeaderMatcher when starting the server, but after updating this no longer works.

I went over the google.golang.org/grpc/metadata package and it seems that every key set in the metadata is transformed to lower case, but the runtime.DefaultHeaderMatcher function compares the transformed metadata key with the prefix "Grpc-Metadata-", so it never matches and the header is never returned.

I think this broke it.

Am I doing anything wrong? How should I set the metadata so it is returned as an HTTP header?

[johanbrandhorst]

Hi @joelurraco, this does indeed sound problematic. The fix seems simple enough, do you think you could contribute a fix and a new test case?

[johanbrandhorst]

Fixed with #784