Add method to get the user agent from the context if set

pkg/ctx/agentctx.go

@@ -0,0 +1,44 @@
+// Copyright 2018-2021 CERN
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// In applying this license, CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+
+package ctx
+
+import (
+	"context"
+
+	ua "github.com/mileusna/useragent"
+	"google.golang.org/grpc/metadata"
+)
+
+// ContextGetUserAgent returns the user agent if set in the given context.
+// see https://github.com/grpc/grpc-go/issues/1100
+func ContextGetUserAgent(ctx context.Context) (*ua.UserAgent, bool) {
+	md, ok := metadata.FromIncomingContext(ctx)
+	if !ok {
+		return nil, false
+	}
+	userAgentLst, ok := md["user-agent"]
+	if !ok {
+		return nil, false
+	}
+	if len(userAgentLst) == 0 {
+		return nil, false
+	}
+	userAgent := ua.Parse(userAgentLst[0])
+	return &userAgent, true
+}