grpc_ctxtags from metadata

[graphaelli]

I'm trying to log some per-request metadata. The code below gets it done, producing:

grpc.code=OK grpc.method=Ping user=98765 peer.address=127.0.0.1:53878 span.kind=server system=grpc

I was wondering if there's a better way?

On the client side doing:

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

md := metadata.Pairs("user", "98765")
ctx := metadata.NewOutgoingContext(context.Background(), md)
client.Ping(ctx, &pb_testproto.PingRequest{})

And on the server, something like:

func UnaryServerMetdataTagInterceptor(fields ...string) grpc.UnaryServerInterceptor {
	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
		if ctxMd, ok := metadata.FromIncomingContext(ctx); ok {
			for _, field := range fields {
				if values, present := ctxMd[field]; present {
					tags := grpc_ctxtags.Extract(ctx)
					tags = tags.Set(field, strings.Join(values, ","))
				}
			}
		}
		return handler(ctx, req)
	}
}

myServer := grpc.NewServer(
	grpc_middleware.WithUnaryServerChain(
		grpc_ctxtags.UnaryServerInterceptor(),
		UnaryServerMetdataTagInterceptor("user"),
		grpc_logrus.UnaryServerInterceptor(logrusEntry, logrusOpts...),
	),
	...
)

Related, is there a reason grpc_ctxtags. RequestFieldExtractorFunc doesn't get access to the per-request context? Would the addition of a MetadataExtractorFunc in grpc_ctxtags.options be welcomed?

[mwitkow]

MetadataExtractorFunc sounds like a good extra options to the tags interceptors. Happy to review PRs! :)

[bwplotka]

This is pretty old and we know have v2 code with different structure. Let us know if this is still important, we can reopen.